(本系列基于Jelly Bean,Android OS4.2,API 17版本) 操作栏Action Bar是在Android3.0版本中引入的，用来替代之前的标题栏。ActionBar提供了更丰富的导航效果，它可用来显示用户动作和全局的菜单选项，还可以增强标识，或者在Fragment之间切换，提供下拉导航栏、显示搜索和分享等动作。. 使用ActionBar很简单，在3.0以后的版本中都默认包含ActionBar组件。如果不想使用，需要将Activity的主题设置为Theme.Holo.NoActionBar： <activity android:theme="@android:style/Theme.Holo.NoActionBar"> 如果仅仅不想显示，可以调用ActionBar.hide()方法，这样当你想显示时，就可以用show()方法达到目的。 本范例中实现了不同版本中ActionBar的兼容功能，一共使用了8个类，下面一一介绍： ActionBarHelper.class处理ActionBar基础功能的抽象类。实现这个类的是下面的两个类： ActionBarHelperBase.class 在3.0以前版本中使用，弄明白这个类也就学会了自定义菜单栏的方法 ActionBarHelperHoneycomb在3.0以后版本中使用，后面的类继承了这个类 ActionBarHelperICS在4.0版本后使用，继承了上面类的大部分方法 SimpleMenu.class和SimpleMenuItem是 用于兼容的类，在低版本上使用。 然后就负责具体交互的Activity类MainActivity，继承自实现了ActionBar功能的ActionBarActivity。 下面着重分析ActionBarHelperBase类
package com.example.android.actionbarcompat;import org.xmlpull.v1.XmlPullParser;import org.xmlpull.v1.XmlPullParserException;import android.app.Activity;import android.content.Context;import android.content.res.XmlResourceParser;import android.os.Bundle;import android.view.InflateException;import android.view.Menu;import android.view.MenuInflater;import android.view.MenuItem;import android.view.View;import android.view.ViewGroup;import android.view.Window;import android.widget.ImageButton;import android.widget.ImageView;import android.widget.LinearLayout;import android.widget.ProgressBar;import android.widget.TextView;import java.io.IOException;import java.util.HashSet;import java.util.Set;/** * 实现了ActionBar的类，用于HoneyComb之前的操作系统版本 */public class ActionBarHelperBase extends ActionBarHelper { private static final String MENU_RES_NAMESPACE = "http://schemas.android.com/apk/res/android"; private static final String MENU_ATTR_ID = "id"; private static final String MENU_ATTR_SHOW_AS_ACTION = "showAsAction"; protected Set<Integer> mActionItemIds = new HashSet<Integer>(); protected ActionBarHelperBase(Activity activity) { super(activity); }@Override public void onCreate(Bundle savedInstanceState) { mActivity.requestWindowFeature(Window.FEATURE_CUSTOM_TITLE); }@Override public void onPostCreate(Bundle savedInstanceState) { mActivity.getWindow().setFeatureInt(Window.FEATURE_CUSTOM_TITLE, R.layout.actionbar_compat); setupActionBar(); SimpleMenu menu = new SimpleMenu(mActivity); mActivity.onCreatePanelMenu(Window.FEATURE_OPTIONS_PANEL, menu); mActivity.onPrepareOptionsMenu(menu); for (int i = 0; i < menu.size(); i++) { MenuItem item = menu.getItem(i); if (mActionItemIds.contains(item.getItemId())) { addActionItemCompatFromMenuItem(item); } } } /** * 设置操作栏 */ private void setupActionBar() { final ViewGroup actionBarCompat = getActionBarCompat(); if (actionBarCompat == null) { return; } LinearLayout.LayoutParams springLayoutParams = new LinearLayout.LayoutParams( 0, ViewGroup.LayoutParams.FILL_PARENT); springLayoutParams.weight = 1; // 添加Home按钮 SimpleMenu tempMenu = new SimpleMenu(mActivity); SimpleMenuItem homeItem = new SimpleMenuItem( tempMenu, android.R.id.home, 0, mActivity.getString(R.string.app_name)); homeItem.setIcon(R.drawable.ic_home); addActionItemCompatFromMenuItem(homeItem); // 添加标题文本 TextView titleText = new TextView(mActivity, null, R.attr.actionbarCompatTitleStyle); titleText.setLayoutParams(springLayoutParams); titleText.setText(mActivity.getTitle()); actionBarCompat.addView(titleText); }@Override public void setRefreshActionItemState(boolean refreshing) { View refreshButton = mActivity.findViewById(R.id.actionbar_compat_item_refresh); View refreshIndicator = mActivity.findViewById( R.id.actionbar_compat_item_refresh_progress); if (refreshButton != null) { refreshButton.setVisibility(refreshing ? View.GONE : View.VISIBLE); } if (refreshIndicator != null) { refreshIndicator.setVisibility(refreshing ? View.VISIBLE : View.GONE); } } /** 下面的代码用来隐藏选项按钮 */@Override public boolean onCreateOptionsMenu(Menu menu) { // Hides on-screen action items from the options menu. for (Integer id : mActionItemIds) { menu.findItem(id).setVisible(false); } return true; }@Override protected void onTitleChanged(CharSequence title, int color) { TextView titleView = (TextView) mActivity.findViewById(R.id.actionbar_compat_title); if (titleView != null) { titleView.setText(title); } } /** * Returns a {@link android.view.MenuInflater} that can read action bar metadata on * pre-Honeycomb devices. */ public MenuInflater getMenuInflater(MenuInflater superMenuInflater) { return new WrappedMenuInflater(mActivity, superMenuInflater); } /** * ViewGroup作为View的一种，被用作容纳多个View的容器，这里返回操作栏上用到的ViewGroup， * 如果是HoneyComb以上安卓版本，返回Null。 */ private ViewGroup getActionBarCompat() { return (ViewGroup) mActivity.findViewById(R.id.actionbar_compat); } /** * Adds an action button to the compatibility action bar, using menu information from a {@link* android.view.MenuItem}. If the menu item ID is <code>menu_refresh</code>, the menu item's * state can be changed to show a loading spinner using * {@link com.example.android.actionbarcompat.ActionBarHelperBase#setRefreshActionItemState(boolean)}. */ private View addActionItemCompatFromMenuItem(final MenuItem item) { final int itemId = item.getItemId(); final ViewGroup actionBar = getActionBarCompat(); if (actionBar == null) { return null; } // 根据版本创建ImageButton ImageButton actionButton = new ImageButton(mActivity, null, itemId == android.R.id.home ? R.attr.actionbarCompatItemHomeStyle : R.attr.actionbarCompatItemStyle); actionButton.setLayoutParams(new ViewGroup.LayoutParams( (int) mActivity.getResources().getDimension( itemId == android.R.id.home ? R.dimen.actionbar_compat_button_home_width : R.dimen.actionbar_compat_button_width), ViewGroup.LayoutParams.FILL_PARENT)); if (itemId == R.id.menu_refresh) { actionButton.setId(R.id.actionbar_compat_item_refresh); } actionButton.setImageDrawable(item.getIcon()); actionButton.setScaleType(ImageView.ScaleType.CENTER); actionButton.setContentDescription(item.getTitle()); actionButton.setOnClickListener(new View.OnClickListener() { public void onClick(View view) { mActivity.onMenuItemSelected(Window.FEATURE_OPTIONS_PANEL, item); } }); actionBar.addView(actionButton); if (item.getItemId() == R.id.menu_refresh) { // Refresh buttons should be stateful, and allow for indeterminate progress indicators, // so add those. ProgressBar indicator = new ProgressBar(mActivity, null, R.attr.actionbarCompatProgressIndicatorStyle); final int buttonWidth = mActivity.getResources().getDimensionPixelSize( R.dimen.actionbar_compat_button_width); final int buttonHeight = mActivity.getResources().getDimensionPixelSize( R.dimen.actionbar_compat_height); final int progressIndicatorWidth = buttonWidth / 2; LinearLayout.LayoutParams indicatorLayoutParams = new LinearLayout.LayoutParams( progressIndicatorWidth, progressIndicatorWidth); indicatorLayoutParams.setMargins( (buttonWidth - progressIndicatorWidth) / 2, (buttonHeight - progressIndicatorWidth) / 2, (buttonWidth - progressIndicatorWidth) / 2, 0); indicator.setLayoutParams(indicatorLayoutParams); indicator.setVisibility(View.GONE); indicator.setId(R.id.actionbar_compat_item_refresh_progress); actionBar.addView(indicator); } return actionButton; } /** * MenuInflater的子类,用来解析定义在Menu目录下的菜单布局文件. */ private class WrappedMenuInflater extends MenuInflater { MenuInflater mInflater; public WrappedMenuInflater(Context context, MenuInflater inflater) { super(context); mInflater = inflater; } @Override public void inflate(int menuRes, Menu menu) { loadActionBarMetadata(menuRes); mInflater.inflate(menuRes, menu); } /** * Loads action bar metadata from a menu resource, storing a list of menu item IDs that * should be shown on-screen (i.e. those with showAsAction set to always or ifRoom).*/ private void loadActionBarMetadata(int menuResId) { XmlResourceParser parser = null; try { parser = mActivity.getResources().getXml(menuResId); int eventType = parser.getEventType(); int itemId; int showAsAction; boolean eof = false; while (!eof) { switch (eventType) { case XmlPullParser.START_TAG: if (!parser.getName().equals("item")) { break; } itemId = parser.getAttributeResourceValue(MENU_RES_NAMESPACE, MENU_ATTR_ID, 0); if (itemId == 0) { break; } showAsAction = parser.getAttributeIntValue(MENU_RES_NAMESPACE, MENU_ATTR_SHOW_AS_ACTION, -1); if (showAsAction == MenuItem.SHOW_AS_ACTION_ALWAYS || showAsAction == MenuItem.SHOW_AS_ACTION_IF_ROOM) { mActionItemIds.add(itemId); } break; case XmlPullParser.END_DOCUMENT: eof = true; break; } eventType = parser.next(); } } catch (XmlPullParserException e) { throw new InflateException("Error inflating menu XML", e); } catch (IOException e) { throw new InflateException("Error inflating menu XML", e); } finally { if (parser != null) { parser.close(); } } } }}
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