The row can also contain views which interact with the underlying data model via the adapter. For example, you can have aCheckbox in your row layout and if the Checkbox is selected, the underlying data is changed.

Android provides specialized fragment and activity classes to simplify list handling.

The classes are the ListActivity class if you want to use lists in activities and the the ListFragment class if you want to use lists in fragments.

You do not have to assign a layout to these elements. If you do not define a layout, the activity or fragment contains a singleListView by default. ListActivity and ListFragment also allow you to override a onListItemClick() method for handling selection of list items.

Both classes allow you to set the adapter to the default ListView via the setListAdapter() method.

The following example code shows a simple ListFragment implementation.

package de.vogella.android.fragments;import android.content.Intent;import android.os.Bundle;import android.view.View;import android.widget.ArrayAdapter;import android.widget.ListView;import android.app.ListFragment;public class MyListFragment extends ListFragment {  @Override  public void onActivityCreated(Bundle savedInstanceState) {    super.onActivityCreated(savedInstanceState);    String[] values = new String[] { "Android", "iPhone", "WindowsMobile",        "Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X",        "Linux", "OS/2" };    ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(),        android.R.layout.simple_list_item_1, values);    setListAdapter(adapter);  }  @Override  public void onListItemClick(ListView l, View v, int position, long id) {    // do something with the data  }} 

The next example code demonstrates the usage of a ListActivity.

package de.vogella.android.listactivity;import android.app.ListActivity;import android.os.Bundle;import android.widget.ArrayAdapter;public class MyListActivity extends ListActivity {  public void onCreate(Bundle icicle) {    super.onCreate(icicle);    String[] values = new String[] { "Android", "iPhone", "WindowsMobile",        "Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X",        "Linux", "OS/2" };    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,        android.R.layout.simple_list_item_1, values);    setListAdapter(adapter);  }} 

You can use a custom layout with ListActivity or ListFragment. In this case the fragment or activity searches in the provided layout for a ListView with the pre-defined android:id attribute set to @android:id/list. This usage is demonstrated by the following code snippet.

<ListView  android:id="@android:id/list"  android:layout_width="match_parent"  android:layout_height="wrap_content" ></ListView> 

You can also use a view with the @android:id/empty ID in your layout. The corresponding activity and fragment shows this view automatically if the ListView is empty and hides it otherwise. For example, you could display an error message in such a view.

Performance is especially important on Android as users expect fast reaction times. Compared to desktop computers an Android device is relatively slow from the hardware perspective.

This part describes how to reduce these operations to implement your custom list adapter efficiently. The default Android adapters like ArrayAdapter are already performance optimized.

Every view which get inflated from an XML layout file will result in a Java object. Inflating layouts and creating Java objects is expensive with regards to time and memory consumption.

In addition using the findViewById() method is relatively time consuming, even though it is not as bad as XML inflating.

A ListView typically contains more data than the number of displayed rows. If the user scrolls the list, then rows and their associated views are being scrolled out of the visible area. The Java objects which represents the rows can be reused for newly visible rows.

If Android determines that a row is not visible anymore, it allows the getView() of the adapter method to reuse the associated view via the convertView parameter.

The adapter can assign new data to the views contained in the view hierarchy of the convertView. This avoids inflating an XML file and creating new Java objects.

In case Android cannot reuse a row, the Android system passes null to the convertView parameter. Therefore the adapter implementation needs to check for this.

A ViewHolder implementation allows to avoid the findViewById() method in an adapter.

A ViewHolder class is typically a static inner class in your adapter which holds references to the relevant views. in your layout. This reference is assigned to the row view as a tag via the setTag() method.

If we receive a convertView object, we can get the instance of the ViewHolder via the getTag() method and assign the new attributes to the views via the ViewHolder reference.

While this sounds complex this is approximately 15 % faster then using the findViewById() method.

The following code shows a performance optimized adapter implementation which reuses existing views and implements the holder pattern.

package de.vogella.android.listactivity;import android.app.Activity;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.ArrayAdapter;import android.widget.ImageView;import android.widget.TextView;public class MyPerformanceArrayAdapter extends ArrayAdapter<String> {  private final Activity context;  private final String[] names;  static class ViewHolder {    public TextView text;    public ImageView image;  }  public MyPerformanceArrayAdapter(Activity context, String[] names) {    super(context, R.layout.rowlayout, names);    this.context = context;    this.names = names;  }  @Override  public View getView(int position, View convertView, ViewGroup parent) {    View rowView = convertView;    // reuse views    if (rowView == null) {      LayoutInflater inflater = context.getLayoutInflater();      rowView = inflater.inflate(R.layout.rowlayout, null);      // configure view holder      ViewHolder viewHolder = new ViewHolder();      viewHolder.text = (TextView) rowView.findViewById(R.id.TextView01);      viewHolder.image = (ImageView) rowView          .findViewById(R.id.ImageView01);      rowView.setTag(viewHolder);    }    // fill data    ViewHolder holder = (ViewHolder) rowView.getTag();    String s = names[position];    holder.text.setText(s);    if (s.startsWith("Windows7") || s.startsWith("iPhone")        || s.startsWith("Solaris")) {      holder.image.setImageResource(R.drawable.no);    } else {      holder.image.setImageResource(R.drawable.ok);    }    return rowView;  }} 

It is good practice to allow the user to undo critical actions. Such a critical action is, for example, the deletion of list items.

A proven pattern to handle this undo option is to offer a selection at the end of the screen. This selection vanishes after a predefined time or once the user continues to interact with the application.

For example, the Gmail application implements such a behavior.

The following description contains an example for implementing an undo action. It uses an animation to phase out the undo button automatically out after a while.

For this example create a new project called com.vogella.android.userinterface.undo based on the BlankTemplate template.

Create the following layout for your activity. It uses a FrameLayout to show two different parts of the user interface. The button bar is initially hidden. The button uses a drawable. Either add such a drawable to your project or remove the reference.

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent" >    <RelativeLayout        android:layout_width="match_parent"        android:layout_height="match_parent"        tools:context=".MainActivity" >        <ListView            android:id="@+id/listview"            android:layout_width="match_parent"            android:layout_height="match_parent" >        </ListView>    </RelativeLayout>    <LinearLayout        android:id="@+id/undobar"        android:visibility="gone"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_gravity="bottom|center_horizontal"        android:layout_margin="20dp"        android:alpha="100"        android:background="#808080"        android:dividerPadding="11dp"        android:padding="4dp" >        <TextView            android:id="@+id/undobar_message"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:text="Deleted"            android:textAppearance="?android:attr/textAppearanceMedium"            android:textColor="#fff" />        <Button            android:id="@+id/undobar_button"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:layout_marginLeft="30dp"            android:onClick="onClick"            android:background="#808080"            android:drawableLeft="@drawable/ic_undobar_undo"            android:text="Undo"            android:textAppearance="?android:attr/textAppearanceMedium"            android:textColor="#fff" />    </LinearLayout></FrameLayout> 

Change your activity so that it is similar to the following code. The Android project wizard in Eclipse already generated anActionBar entry. This entry is used in the following code. If in doubt, create your own ActionBar entry.

package com.vogella.android.userinterface.undo;import android.app.Activity;import android.os.Bundle;import android.view.Menu;import android.view.MenuItem;import android.view.View;import android.widget.ArrayAdapter;import android.widget.ListView;import android.widget.Toast;import com.vogella.android.actionbar.undo.R;public class MainActivity extends Activity {  private View viewContainer;  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    ListView l = (ListView) findViewById(R.id.listview);    String[] values = new String[] { "Ubuntu", "Android", "iPhone",        "Windows", "Ubuntu", "Android", "iPhone", "Windows" };    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,        android.R.layout.simple_list_item_1, values);    viewContainer = findViewById(R.id.undobar);    l.setAdapter(adapter);  }  @Override  public boolean onCreateOptionsMenu(Menu menu) {    // Inflate the menu; this adds items to the action bar if it is present.    getMenuInflater().inflate(R.menu.activity_main, menu);    return true;  }  @Override  public boolean onOptionsItemSelected(MenuItem item) {    showUndo(viewContainer);    return true;  }  public void onClick(View view) {    Toast.makeText(this, "Deletion undone", Toast.LENGTH_LONG).show();    viewContainer.setVisibility(View.GONE);  }  public static void showUndo(final View viewContainer) {    viewContainer.setVisibility(View.VISIBLE);    viewContainer.setAlpha(1);    viewContainer.animate().alpha(0.4f).setDuration(5000)        .withEndAction(new Runnable() {          @Override          public void run() {            viewContainer.setVisibility(View.GONE);          }        });  }} 

If you select the entry in the ActionBar, the button bar becomes visible for 5 seconds.

Frequently you need to select items in your ListView. As the row of the ListView are getting recycled you cannot store the selection on the View level.

Selection is just one possible example but you can imange other interaction between your row and model.

To persist the selection you have to update your data model with the selected state.

To update the data model in your ListView you define your own Adapter class. In this adapter class you attach a listener to theView which is responsible for selecting the model element. If selected you update the state in the model which you can add as a tag to the View to have access to it.

The following example demonstrates how to use standard Java object and how to interact from the Views with the model.

Continue to use the de.vogella.android.listactivity project.

Create the following Model which hold the name and the information if this element is currently selected.

package de.vogella.android.listactivity;public class Model {  private String name;  private boolean selected;  public Model(String name) {    this.name = name;    selected = false;  }  public String getName() {    return name;  }  public void setName(String name) {    this.name = name;  }  public boolean isSelected() {    return selected;  }  public void setSelected(boolean selected) {    this.selected = selected;  }} 

Create the following new layout file called rowbuttonlayout.xml.

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="wrap_content" >    <TextView        android:id="@+id/label"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="@+id/label"        android:textSize="30px" >    </TextView>    <CheckBox        android:id="@+id/check"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_alignParentRight="true"        android:layout_marginLeft="4px"        android:layout_marginRight="10px" >    </CheckBox></RelativeLayout> 

Create the following Adapter. This adapter adds a listener on the Checkbox view . If the checkbox is selected the underlying data of the model is changed. Checkbox gets the corresponding model element assigned via the getTag() method.

package de.vogella.android.listactivity;import java.util.List;import android.app.Activity;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.ArrayAdapter;import android.widget.CheckBox;import android.widget.CompoundButton;import android.widget.TextView;public class InteractiveArrayAdapter extends ArrayAdapter<Model> {  private final List<Model> list;  private final Activity context;  public InteractiveArrayAdapter(Activity context, List<Model> list) {    super(context, R.layout.rowbuttonlayout, list);    this.context = context;    this.list = list;  }  static class ViewHolder {    protected TextView text;    protected CheckBox checkbox;  }  @Override  public View getView(int position, View convertView, ViewGroup parent) {    View view = null;    if (convertView == null) {      LayoutInflater inflator = context.getLayoutInflater();      view = inflator.inflate(R.layout.rowbuttonlayout, null);      final ViewHolder viewHolder = new ViewHolder();      viewHolder.text = (TextView) view.findViewById(R.id.label);      viewHolder.checkbox = (CheckBox) view.findViewById(R.id.check);      viewHolder.checkbox          .setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {            @Override            public void onCheckedChanged(CompoundButton buttonView,                boolean isChecked) {              Model element = (Model) viewHolder.checkbox                  .getTag();              element.setSelected(buttonView.isChecked());            }          });      view.setTag(viewHolder);      viewHolder.checkbox.setTag(list.get(position));    } else {      view = convertView;      ((ViewHolder) view.getTag()).checkbox.setTag(list.get(position));    }    ViewHolder holder = (ViewHolder) view.getTag();    holder.text.setText(list.get(position).getName());    holder.checkbox.setChecked(list.get(position).isSelected());    return view;  }} 

Finally change your activity to the following.

package de.vogella.android.listactivity;import java.util.ArrayList;import java.util.List;import android.app.ListActivity;import android.os.Bundle;import android.widget.ArrayAdapter;public class MyList extends ListActivity {  
/** Called when the activity is first created. */
  public void onCreate(Bundle icicle) {    super.onCreate(icicle);    // create an array of Strings, that will be put to our ListActivity    ArrayAdapter<Model> adapter = new InteractiveArrayAdapter(this,        getModel());    setListAdapter(adapter);  }  private List<Model> getModel() {    List<Model> list = new ArrayList<Model>();    list.add(get("Linux"));    list.add(get("Windows7"));    list.add(get("Suse"));    list.add(get("Eclipse"));    list.add(get("Ubuntu"));    list.add(get("Solaris"));    list.add(get("Android"));    list.add(get("iPhone"));    // Initially select one of the items    list.get(1).setSelected(true);    return list;  }  private Model get(String s) {    return new Model(s);  }} 

If you start your app you should be able to flag items. These changes will be reflected in your model.

The ExpandableListView is similar to ListView but allow you to define groups and details for this group. ExpandableListViewexpects and adapter of type BaseExpandableListAdapter.

In this case you have to define two layouts, one for the group and another one for the details row.

In the following example you create an expandable listview similar to the following screenshot.

Create a project called com.vogella.android.listview.expandable with the activity called MainActivity.

Create or adjust the following layout files. First layout/activity_main.xml.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:id="@+id/LinearLayout1"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:paddingBottom="@dimen/activity_vertical_margin"    android:paddingLeft="@dimen/activity_horizontal_margin"    android:paddingRight="@dimen/activity_horizontal_margin"    android:paddingTop="@dimen/activity_vertical_margin"    tools:context=".MainActivity" >    <ExpandableListView        android:id="@+id/listView"        android:layout_width="match_parent"        android:layout_height="wrap_content" >    </ExpandableListView></LinearLayout> 

Afterwards create layout/listrow_group.xml.

<CheckedTextView xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:id="@+id/textView1"    android:layout_width="wrap_content"    android:layout_height="?android:attr/listPreferredItemHeight"    android:layout_marginLeft="8dp"    android:drawableRight="@drawable/ic_launcher"    android:gravity="left"    android:paddingLeft="32dp"    android:paddingTop="8dp"    android:text="Test"    android:textSize="14sp"    android:textAlignment="textEnd"    android:textStyle="bold" /> 

The last required layout is layout/listrow_details.xml.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="40dp"    android:clickable="true"    android:orientation="vertical"    android:paddingLeft="40dp"    tools:context=".MainActivity" >    <TextView        android:id="@+id/textView1"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:drawableLeft="@drawable/ic_launcher"        android:drawablePadding="5dp"        android:gravity="center_vertical"        android:text="@string/hello_world"        android:textSize="14sp"        android:textStyle="bold" >    </TextView>    <View        android:layout_width="match_parent"        android:layout_height="1dp"        android:background="@android:color/black" /></LinearLayout> 

Create the following class which hold your domain model for the ExpandableListView.

package com.vogella.android.listview.expandable;import java.util.ArrayList;import java.util.List;public class Group {  public String string;  public final List<String> children = new ArrayList<String>();  public Group(String string) {    this.string = string;  }} 

Finally create the adapter as described by the following listing and change the activity to the code provided below.

package com.vogella.android.listview.expandable;import android.app.Activity;import android.util.SparseArray;import android.view.LayoutInflater;import android.view.View;import android.view.View.OnClickListener;import android.view.ViewGroup;import android.widget.BaseExpandableListAdapter;import android.widget.CheckedTextView;import android.widget.TextView;import android.widget.Toast;public class MyExpandableListAdapter extends BaseExpandableListAdapter {  private final SparseArray<Group> groups;  public LayoutInflater inflater;  public Activity activity;  public MyExpandableListAdapter(Activity act, SparseArray<Group> groups) {    activity = act;    this.groups = groups;    inflater = act.getLayoutInflater();  }  @Override  public Object getChild(int groupPosition, int childPosition) {    return groups.get(groupPosition).children.get(childPosition);  }  @Override  public long getChildId(int groupPosition, int childPosition) {    return 0;  }  @Override  public View getChildView(int groupPosition, final int childPosition,      boolean isLastChild, View convertView, ViewGroup parent) {    final String children = (String) getChild(groupPosition, childPosition);    TextView text = null;    if (convertView == null) {      convertView = inflater.inflate(R.layout.listrow_details, null);    }    text = (TextView) convertView.findViewById(R.id.textView1);    text.setText(children);    convertView.setOnClickListener(new OnClickListener() {      @Override      public void onClick(View v) {        Toast.makeText(activity, children,            Toast.LENGTH_SHORT).show();      }    });    return convertView;  }  @Override  public int getChildrenCount(int groupPosition) {    return groups.get(groupPosition).children.size();  }  @Override  public Object getGroup(int groupPosition) {    return groups.get(groupPosition);  }  @Override  public int getGroupCount() {    return groups.size();  }  @Override  public void onGroupCollapsed(int groupPosition) {    super.onGroupCollapsed(groupPosition);  }  @Override  public void onGroupExpanded(int groupPosition) {    super.onGroupExpanded(groupPosition);  }  @Override  public long getGroupId(int groupPosition) {    return 0;  }  @Override  public View getGroupView(int groupPosition, boolean isExpanded,      View convertView, ViewGroup parent) {    if (convertView == null) {      convertView = inflater.inflate(R.layout.listrow_group, null);    }    Group group = (Group) getGroup(groupPosition);    ((CheckedTextView) convertView).setText(group.string);    ((CheckedTextView) convertView).setChecked(isExpanded);    return convertView;  }  @Override  public boolean hasStableIds() {    return false;  }  @Override  public boolean isChildSelectable(int groupPosition, int childPosition) {    return false;  }} 

package com.vogella.android.listview.expandable;import java.util.ArrayList;import android.app.Activity;import android.os.Bundle;import android.util.SparseArray;import android.view.Menu;import android.widget.ExpandableListView;public class MainActivity extends Activity {  // more efficient than HashMap for mapping integers to objects  SparseArray<Group> groups = new SparseArray<Group>();  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    createData();    ExpandableListView listView = (ExpandableListView) findViewById(R.id.listView);    MyExpandableListAdapter adapter = new MyExpandableListAdapter(this,        groups);    listView.setAdapter(adapter);  }  public void createData() {    for (int j = 0; j < 5; j++) {      Group group = new Group("Test " + j);      for (int i = 0; i < 5; i++) {        group.children.add("Sub Item" + i);      }      groups.append(j, group);    }  }} 

You can also add a LongItemClickListener to the View. For this receive the ListView via the getListVIew() method and set the LongItemClickListener via the setOnItemLongClickListener() method.

package de.vogella.android.listactivity;import android.app.ListActivity;import android.os.Bundle;import android.view.View;import android.widget.AdapterView;import android.widget.AdapterView.OnItemLongClickListener;import android.widget.ArrayAdapter;import android.widget.ListView;import android.widget.Toast;public class MyList extends ListActivity {  
/** Called when the activity is first created. */
  public void onCreate(Bundle icicle) {    super.onCreate(icicle);    // create an array of Strings, that will be put to our ListActivity    String[] names = new String[] { "Linux", "Windows7", "Eclipse", "Suse",        "Ubuntu", "Solaris", "Android", "iPhone" };    ArrayAdapter<String> adapter = new MyPerformanceArrayAdapter(this, names);    setListAdapter(adapter);    ListView list = getListView();    list.setOnItemLongClickListener(new OnItemLongClickListener() {      @Override      public boolean onItemLongClick(AdapterView<?> parent, View view,          int position, long id) {        Toast.makeText(MyList.this,            "Item in position " + position + " clicked",            Toast.LENGTH_LONG).show();        // Return true to consume the click event. In this case the        // onListItemClick listener is not called anymore.        return true;      }    });  }  @Override  protected void onListItemClick(ListView l, View v, int position, long id) {    super.onListItemClick(l, v, position, id);    // Get the item that was clicked    Object o = this.getListAdapter().getItem(position);    String keyword = o.toString();    Toast.makeText(this, "You selected: " + keyword, Toast.LENGTH_SHORT)        .show();  }} 

You can of course put arbitrary Views elements around your ListView. For example you can define a layout with two TextViewsand a ListView between them. In this case the two TextViews will always be visible above the List (header) and the other will be visible below the ListView. If you want to display a list header or list footer only at the see the beginning or end of the list you can use the addHeaderView() method or addFooterView() method on the ListView class.

package de.vogella.android.listactivity;import android.app.ListActivity;import android.os.Bundle;import android.view.View;import android.widget.ArrayAdapter;import android.widget.ListView;public class MyList extends ListActivity {  
/** Called when the activity is first created. */
  public void onCreate(Bundle icicle) {    super.onCreate(icicle);    // create an array of Strings, that will be put to our ListActivity    String[] names = new String[] { "Linux", "Windows7", "Eclipse", "Suse",        "Ubuntu", "Solaris", "Android", "iPhone", "Linux", "Windows7",        "Eclipse", "Suse", "Ubuntu", "Solaris", "Android", "iPhone" };    View header = getLayoutInflater().inflate(R.layout.header, null);    View footer = getLayoutInflater().inflate(R.layout.footer, null);    ListView listView = getListView();    listView.addHeaderView(header);    listView.addFooterView(footer);    setListAdapter(new ArrayAdapter<String>(this,        android.R.layout.simple_list_item_single_choice,        android.R.id.text1, names));  }} 

Android提供了专门的片段和活动课，以简化处理列表。

该班 ??是ListActivity类，如果你想使用列表中的活动和在ListFragment ，如果你想使用列表中的片段类。

你不必布局分配给这些元素。 如果你没有定义布局，活动或片段包含一个ListView默认。 ListActivity和ListFragment还允许您重写onListItemClick()方法来处理选择列表中的项目。

这两个类允许您设置适配器默认ListView通过setListAdapter()方法。

下面的示例代码显示了一个简单的ListFragment实现。

接下来的示例代码演示的使用ListActivity 。

你可以使用一个自定义布局ListActivity或ListFragment 。 在这种情况下，该片段或活性的搜索在为提供布局ListView与预先定义android:id属性设置为@android:id/list 。 这种用法表现在下面的代码片段。

您还可以使用与视图@android:id/empty在布局ID。 相应的活动和片段显示了这一观点自动如果ListView是空的，否则隐藏它。 例如，你可以在这样一个视图中显示错误消息。

性能在Android上尤其重要，因为用户所期望的快速的反应时间。 与台式机相比Android设备是从硬件的角度来看相对缓慢。

这部分介绍如何减少这些操作有效地实现您的自定义列表适配器。 默认的Android适配器像ArrayAdapter已经优化性能。

这从一个XML布局文件得到充气每个视图将导致Java对象。 充气布局和创建Java对象是昂贵的问候时间和内存消耗。

除了 ??使用findViewById()方法比较费时，即使它不是那么糟糕，因为XML膨胀。

一个ListView通常包含比显示的行数更多的数据。 如果用户滚动列表中，则行和与其相关的意见正在滚动出可视区域的。 它代表行的Java对象可以再次用于新的可见行。

如果Android的确定一个行不再可见，它允许getView()适配器方法重用通过相关视图convertView参数。

该适配器可以将新的数据包含在的视图层次的意见convertView 。 这避免了膨胀的XML文件，并创建新的Java对象。

在Android的情况下，不能再使用一排，Android系统传递null到convertView参数。 因此适配器实现需要检查这一点。

一个ViewHolder实现允许避免findViewById()在适配器的方法。

一ViewHolder类通常是在你的适配器持有引用相关意见静态内部类。 在您的布局。 该参考分配给行视图，经由一个标签setTag()方法。

如果我们收到convertView对象，我们可以得到的实例ViewHolder通过getTag()方法，并指定新的属性通过意见ViewHolder参考。

虽然这听起来复杂，这是更快的约15％，然后使用findViewById()方法。

下面的代码显示了一个性能优化的适配器实现其重用现有的意见，并实现了持有人格局。

这是很好的做法，以允许用户撤消关键行动。 这样一个关键的动作是，例如，删除的列表项。

甲证明图案来处理这种撤消选项是提供一种选择在屏幕的末端。 后的预定时间该选择消失或者一旦用户继续与应用程序交互。

例如，Gmail应用程序实现了这样的行为。

下面的描述包含用于实现撤消操作的一个例子。它使用动画来自动淘汰撤销按钮了一段时间后。

在这个例子中创建一个名为新项目com.vogella.android.userinterface.undo基础上，BlankTemplate模板。

为您的布局如下活动。它使用的FrameLayout显示用户接口的两个不同的部分。按钮栏最初是隐藏的。按钮采用了绘制。无论是添加这样的绘制到项目或删除引用。

 <FrameLayout  xmlns:android = "http://schemas.android.com/apk/res/android"     xmlns:tools = "http://schemas.android.com/tools"     android:layout_width = "match_parent"     android:layout_height = "match_parent"  >    <RelativeLayout         android:layout_width = "match_parent"         android:layout_height = "match_parent"         tools:context = ".MainActivity"  >        <ListView             android:id = "@+id/listview"             android:layout_width = "match_parent"             android:layout_height = "match_parent"  >         </ListView>     </RelativeLayout>    <LinearLayout         android:id = "@+id/undobar"         android:visibility = "gone"         android:layout_width = "wrap_content"         android:layout_height = "wrap_content"         android:layout_gravity = "bottom|center_horizontal"         android:layout_margin = "20dp"         android:alpha = "100"         android:background = "#808080"         android:dividerPadding = "11dp"         android:padding = "4dp"  >        <TextView             android:id = "@+id/undobar_message"             android:layout_width = "wrap_content"             android:layout_height = "wrap_content"             android:text = "Deleted"             android:textAppearance = "?android:attr/textAppearanceMedium"             android:textColor = "#fff"  />        <Button             android:id = "@+id/undobar_button"             android:layout_width = "wrap_content"             android:layout_height = "wrap_content"             android:layout_marginLeft = "30dp"             android:onClick = "onClick"             android:background = "#808080"             android:drawableLeft = "@drawable/ic_undobar_undo"             android:text = "Undo"             android:textAppearance = "?android:attr/textAppearanceMedium"             android:textColor = "#fff"  />     </ LinearLayout中></的FrameLayout> 

改变你的活动，使其类似于下面的代码。在Eclipse中的Android项目向导已经生成的动作条条目。本条目中使用以下代码。如有疑问，创建自己的动作条条目。

如果您选择的入门动作条，按钮栏变为显示5秒钟。

经常，你需要选择你的项目的ListView。由于排的ListView越来越回收你不能存储在选择视图的水平。

选择只是一种可能的例子，但你可以imange你行和模型之间的相互作用等。

坚持你必须与选定的状态更新数据模型的选择。

更新您的数据模型的ListView你定义自己的适配器类。在这个适配器类附加一个监听到视图负责选择模型元素。如果您选择更新，你可以作为一个标签添加到视图来访问它的模型的状态。

下面的例子演示了如何使用标准的Java对象，如何从交互视图和模型。

继续使用de.vogella.android.listactivity项目。

创建以下模型如果该元素是当前选择哪个保持的名称和信息。

创建一个名为以下新布局文件rowbuttonlayout.xml。

创建以下适配器。此适配器加上了一个侦听器复选框观点。如果该复选框被选中的模式的基础数据被改变。复选框获取经由所分配的相应的模型元素getTag（）方法。

最后，您更改活动以下内容。

如果你开始你的应用程序，你应该能够标志的物品。这些变化将反映在您的模型。

该ExpandableListView类似的ListView但允许您定义组和详细信息该组。ExpandableListView预期和类型的适配器BaseExpandableListAdapter。

在这种情况下，你必须定义两个布局，一个组，另一个用于详情一行。

在下面的例子中，你创建一个类似于下面的截图可扩展列表视图。

创建了一个名为com.vogella.android.listview.expandable与所谓的活动MainActivity。

创建或调整下列布局文件。一是布局/ activity_main.xml。

 <LinearLayout  xmlns:android = "http://schemas.android.com/apk/res/android"     xmlns:tools = "http://schemas.android.com/tools"     android:id = "@+id/LinearLayout1"     android:layout_width = "match_parent"     android:layout_height = "match_parent"     android:paddingBottom = "@dimen/activity_vertical_margin"     android:paddingLeft = "@dimen/activity_horizontal_margin"     android:paddingRight = "@dimen/activity_horizontal_margin"     android:paddingTop = "@dimen/activity_vertical_margin"     tools:context = ".MainActivity"  >    <ExpandableListView         android:id = "@+id/listView"         android:layout_width = "match_parent"         android:layout_height = "wrap_content"  >     </ExpandableListView> </ LinearLayout中> 

随后创建布局/ listrow_group.xml。

 <CheckedTextView  xmlns:android = "http://schemas.android.com/apk/res/android"     xmlns:tools = "http://schemas.android.com/tools"     android:id = "@+id/textView1"     android:layout_width = "wrap_content"     android:layout_height = "?android:attr/listPreferredItemHeight"     android:layout_marginLeft = "8dp"     android:drawableRight = "@drawable/ic_launcher"     android:gravity = "left"     android:paddingLeft = "32dp"     android:paddingTop = "8dp"     android:text = "Test"     android:textSize = "14sp"     android:textAlignment = "textEnd"     android:textStyle = "bold"  /> 

最后所需的布局布局/ listrow_details.xml。

 <LinearLayout  xmlns:android = "http://schemas.android.com/apk/res/android"     xmlns:tools = "http://schemas.android.com/tools"     android:layout_width = "match_parent"     android:layout_height = "40dp"     android:clickable = "true"     android:orientation = "vertical"     android:paddingLeft = "40dp"     tools:context = ".MainActivity"  >    <TextView         android:id = "@+id/textView1"         android:layout_width = "wrap_content"         android:layout_height = "wrap_content"         android:drawableLeft = "@drawable/ic_launcher"         android:drawablePadding = "5dp"         android:gravity = "center_vertical"         android:text = "@string/hello_world"         android:textSize = "14sp"         android:textStyle = "bold"  >     </TextView>    <View         android:layout_width = "match_parent"         android:layout_height = "1dp"         android:background = "@android:color/black"  /> </ LinearLayout中> 

创建占据着为你的域模型下面的类ExpandableListView。

最后创建适配器所描述的以下列表并改变活动下面提供的代码。

您还可以添加LongItemClickListener的视图。对于这个接收的ListView经由getListVIew（）方法，并设置LongItemClickListener经由setOnItemLongClickListener（）方法。

当然，你可以把任意查看你周围的ListView元素。例如，你可以定义两个布局TextViews和ListView控件之间。在这种情况下，两个TextViews总是会名单（头）以上可见，另一个是下面的ListView可见。如果你只想在显示列表页眉或页脚列表中看到您可以使用该列表的开头或结尾addHeaderView（）方法或addFooterView（）上的方法的ListView类。