android开发常见有关问题集

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• www.androidkaifa.com提示:Issue意思： 问题，Solution意思：解决方案
• Development
  
  • [Issue] Application crush when return from predefined interface
    [Solution 1] You may forgot to call the method of predefined super class
    i.e.: In your Activity, if you override onDestroy as following:
    class YourActivity extends Activity
    {
        protected void onDestroy()
        {
        }
    }
    when the activity is destroyed, application will crash, in order to resolve this issue, you must modify the code snip to:
    class YourActivity extends Activity
    {
        protected void onDestroy()
        {
            super.onDestroy();  //Call the same method of super class
        }
    }
  • [Issue] Explain view's attributes
       android:gravity: Define which direction to align control's contents.
  • [Issue] How to get and Set system property
    [Solution] Use methods System.getProperty(xxx) and System.setProperty(xxx), following properties can be got and set:
            java.vendor.url
            java.class.path
            user.home
            java.class.version
            os.version
            java.vendor
            user.dir
            user.timezone
            path.separator
            os.name
            os.arch
            line.separator
            file.separator
            user.name
            java.version
            java.home
  • [Issue] How to get popular directories and their stat
    [Sulotion] Call method android.os.Environment, following directories can be received:
       a) root directory
       b) external storage directory
       c) data directory
       d) download cache directory
       e) external storage state,  
    Note: USB mass storage path is /sdcard
  • [Issue] How to access resource in package in Acrivity
    - Get resource value
       getResources().getString(resID);  //resID looks like R.string.str_id
    - Get resource id from name
       getResources().getIdentifier("name", "string", getPackageName());
       getResources().getIdentifier("name", "drawable", getPackageName());
  • [Issue] How to get and  set environment variables
    [Solution] To get the value of the specified environment variables, just use System.getenv(xxx); But you can't set environment variable in Java code directly, you need to use jni to call C function 'setenv'.
  • [Issue] How to know byte order of device
    [Solution] Call method ByteOrder.nativeOrder();
  • [Issue] How to read files in the directories res/raw
    [Sulotion]
    Resources res = getResources();
    InputStream is = res.openRawResource(R.raw.xxx);
  • [Issue] How to display horizontal bar in widget
    [Solution] Use a view which background is filled with the specified color.
    <TableLayout xxxxxx>
        <TableRow xxxxxx>
           ......
        </TableRow>
        ......
        <View android:layout_height="2dip"
            android:background="#FF909090" />
        ......
    </TableLayout>
    
    Comments:
    1) A control View with the specified background is shown as a bar
    2) The View must be declared within TableLayout
    3)If your want to implement the horizontal bar with left/right edgesfading just like ListView's divider, you only need to setandroid:background to "?android:attr/listDivider"
  • [Issue] How to change contents of TextView
    - Set text view to be editable
        TextView textView = findViewById(xxx);
        textView.setText(textView.getText(), TextView.BufferType.EDITABLE);
    - Change contents
        textView.setText(xxx);
        textView.append(xxx);
  • [Issue] Customize View
    - Define customized view class as following
        package com.test.customized;
        import xxxxxx;
        class CustomizedTextView
        {
            private static String HEADER = "(Warning)";
            private static String RETURN = "\n";
    
    
            public TextView(Context context)
            {
                super(context);
            }
       
            public TextView(Context context, AttributeSet attrs)
            {
                super(context, attrs);
            }
    
            public TextView(Context context, AttributeSet attrs, int     defStyle)
            {
                super(context, attrs, defStyle);
            }
    
    
            public void append(CharSequence text, int start, int end)
            {
                super.append(HEADER, 0, HEADERS.length());
                super.append(text, start, end);
                super.append(RETURN, 0, RETURN.length());
            }
        }
    
    - Use the customized view as following
        <?xml version="1.0" encoding="utf-8"?>
        <com.test.customized.CustomizedTextView
          xmlns:android="http://schemas.android.com/apk/res/android"
          android:layout_width="fill_parent"
          android:layout_height="fill_parent"
          android:text="Hello, Android"/>
  • [Issue] How to use multiple Activity
    [Solution] Please refer to:
    http://www.apkcn.com/android-80860-1-1.html
    http://blog.csdn.net/Class_Raito/archive/2008/11/27/3390737.aspx
  • [Issue] How to launch activity
    [Solution]
    Launch application
    1) From shell
      usage: am [start|instrument]
           am start [-a <ACTION>] [-d <DATA_URI>] [-t <MIME_TYPE>]
                    [-c <CATEGORY> [-c <CATEGORY>] ...]
                    [-e <EXTRA_KEY> <EXTRA_VALUE> [-e <EXTRA_KEY> <EXTRA_VALUE> ...]
                    [-n <COMPONENT>] [-D] [<URI>]
           am instrument [-e <ARG_NAME> <ARG_VALUE>] [-p <ROF_FILE>]
                    [-w] <COMPONENT>
            
    For example, launch an application whose manifest are:
            
    <?xml version="1.0" encoding="utf-8"?>
    <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="net.xiashou.android">   
        <application>
            <activity>
              <intent-filter>  
                <categoryandroid:name="android.intent.category.LAUNCHER" />   
              </intent-filter>
            </activity>
        </application>
    </manifest>
            
    Command is: #am start -n net.xiashou.android/net.xiashou.android.HelloAndroid      
    
    Other usage:
    a) Launch browser to open an URI: #am start -a android.intent.action.VIEW -d http://www.xiashou.net
    b) Call out: #am start -a android.intent.action.CALL -d tel:10086
    c) Launch google map to locate TianJing: #am start -a android.intent.action.VIEWgeo:0,0?q=tianjin
    
    2) From on activate:
    Use Intent.
    For example, launch an activate whose manifest is:
    <?xml version="1.0" encoding="utf-8"?>
    <manifest xmlns:android="http://schemas.android.com/apk/res/android"
        package="koushikdutta.superuser" android:versionCode="1"
        android:versionName="1.0.0">
    
        <permission android:name="android.permission.ACCESS_SUPERUSER"
            android:label="@string/superuser_permissions_name"
            android:description="@string/superuser_permissions_description"
            android:protectionLevel="dangerous" />
    
        <application android:icon="@drawable/icon" android:label="@string/app_name"
            android:debuggable="true">
            <activity android:name=".SuperuserActivity" android:label="Superuser Whitelist">
                <intent-filter>
                    <action android:name="android.intent.action.MAIN" />
                    <category android:name="android.intent.category.LAUNCHER" />
                </intent-filter>
            </activity>
            <activity android:name=".SuperuserRequestActivity"
                android:label="Superuser" android:permission="android.permission.ACCESS_SUPERUSER">
                <intent-filter>
                    <action android:name="android.intent.action.superuser" />
                    <category android:name="android.intent.category.DEFAULT" />
                </intent-filter>
            </activity>
        </application>
    </manifest>
    
    
    Launch code is:
    Intent intent = new Intent("android.intent.action.superuser");
    startActivityForResult(intent, SUPERUSER_REQUEST);
  • [Issue] How to close current Activity and remove it from Activityhistory stack when you switch to other Activity
    [Solution] Call"finish()" in current Activity's methods.
  • [Issue] How to use class "Cursor"
    [Solution] Cursor stores the results of database query, such asContentResolver.query(xxxxx), Cursor contains M(Rows) x N (Columns) eluments,each column has its name and value, we can get them by callinggetColumnName() and getString/getInt()/getLong()/getShort()..... etcrespectively.
  • [Issue] How to send Http request
    [Solution] Use folloing code:
    (refer to
    http://blog.atrexis.com/index.cfm/2008/6/20/Sending-HTTP-requests-in-Android
    http://dotphone.org/redirect.php?tid=33&goto=lastpost
    http://dev.shufou.com/?p=28
    )
    
        URL url = new URL("www.baidu.com");
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setDoInput(true);
        conn.setConnectTimeout(10000);
        conn.setRequestMethod(HttpURLConnection.GET);
        conn.setRequestProperty("accept", "*/*");
        String location = conn.getRequestProperty("location");
        int resCode = conn.getResponseCode();
        InputStream stream = conn.getInputStream();
  • [Issue] Java Network exception
    - When establish network connection using socket, SocketException isthrowed, and exception readable string is: "java.net.SocketException:Connection reset".
    Solution: add android.permission.INTERNET to application manifest
    - Android java.net.SocketException: The connection was reset
    Reason: The time out value is too long, try 10 seconds.