google android training:基本网络的管理 转自http://blog.csdn.net/kesenhoo

Managing Network Usage [管理网络的惯用法]

 

Check a Device's Network Connection [检查设备的网络连接信息]

 

 

  • 设备可以有许多种网络连接。关于所有可能的网络连接类型，请看 ConnectivityManager.
  • 通常Wi-Fi是比较快的。移动数据通常都是需要按流量计费，会比较贵。[说起这个，大陆的运营商实在太黑了]. 通常我们会选择让app在连接到WiFi时去获取大量的数据。
  • 那么，我们就需要在执行网络操作之前检查当前连接的网络信息。这样可以防止你的程序不经意连接使用了非意向的网络频道。为了实现这个目的，我们需要使用到下面两个类：
    • ConnectivityManager: Answers queries about the state of network connectivity. It also notifies applications when network connectivity changes.
    • NetworkInfo: Describes the status of a network interface of a given type (currently either Mobile or Wi-Fi).
  • 下面示例了检查WiFi与Mobile是否连接上(请注意available与isConnected的区别)：
privatestaticfinalString DEBUG_TAG ="NetworkStatusExample";...      
ConnectivityManager connMgr =(ConnectivityManager) 
        getSystemService(Context.CONNECTIVITY_SERVICE);NetworkInfo networkInfo = connMgr.getNetworkInfo(ConnectivityManager.TYPE_WIFI);boolean isWifiConn = networkInfo.isConnected();
networkInfo = connMgr.getNetworkInfo(ConnectivityManager.TYPE_MOBILE);boolean isMobileConn = networkInfo.isConnected();Log.d(DEBUG_TAG,"Wifi connected: "+ isWifiConn);Log.d(DEBUG_TAG,"Mobile connected: "+ isMobileConn);
  • 一个更简单的检查网络是否可用的示例如下：
publicboolean isOnline(){
    ConnectivityManager connMgr =(ConnectivityManager) 
            getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
    return(networkInfo !=null&& networkInfo.isConnected());}  

Manage Network Usage [管理网络使用]

  • 你可以实现一个偏好设置的activity ，来允许用户设置程序的网络资源的使用。例如:
    • 你可以允许用户在仅仅连接到WiFi时上传视频。
    • 你可以根据诸如网络可用等条件来选择是否做同步的操作。
  • 网络操作需要添加下面的权限：
  • 你可以为你的设置Activity声明intent filter for the ACTION_MANAGE_NETWORK_USAGE action (introduced in Android 4.0),这样你的这个activity就可以提供数据控制的选项了。在章节概览提供的Sample中，这个action is handled by the class SettingsActivity, 它提供了偏好设置UI来让用户决定何时进行下载。
<?xml version="1.0" encoding="utf-8"?><manifestxmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.android.networkusage"
    ...>

    <uses-sdkandroid:minSdkVersion="4" 
           android:targetSdkVersion="14"/>
        
    <uses-permissionandroid:name="android.permission.INTERNET"/>
    <uses-permissionandroid:name="android.permission.ACCESS_NETWORK_STATE"/>

    <application
        ...>
        ...
        <activityandroid:label="SettingsActivity"android:name=".SettingsActivity">
             <intent-filter>
                <actionandroid:name="android.intent.action.MANAGE_NETWORK_USAGE"/>
                <categoryandroid:name="android.intent.category.DEFAULT"/>
          </intent-filter>
        </activity>
    </application></manifest>

Implement a Preferences Activity [实现一个偏好设置activity]

  • 正如上面看到的那样，SettingsActivity is a subclass ofPreferenceActivity.
  • 所实现的功能见下图：

  • 下面是一个 SettingsActivity. 请注意它实现了OnSharedPreferenceChangeListener. 当用户改变了他的偏好，就会触发 onSharedPreferenceChanged(), 这个方法会设置refreshDisplay 为true[这里的变量存在于自己定义的activity，见下一部分的代码示例]. 这会使的当用户返回到main activity的时候进行refresh。[请注意，代码中的注释，不得不说，Googler写的Code看起来就是舒服]
publicclassSettingsActivityextendsPreferenceActivityimplementsOnSharedPreferenceChangeListener{
    
    @Override
    protectedvoid onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        
        // Loads the XML preferences file
        addPreferencesFromResource(R.xml.preferences);
    }
  
    @Override
    protectedvoid onResume(){
        super.onResume();

        // Registers a listener whenever a key changes            
        getPreferenceScreen().getSharedPreferences().registerOnSharedPreferenceChangeListener(this);
    }
  
    @Override
    protectedvoid onPause(){
        super.onPause();

       // Unregisters the listener set in onResume().
       // It's best practice to unregister listeners when your app isn't using them to cut down on 
       // unnecessary system overhead. You do this in onPause().            
       getPreferenceScreen().getSharedPreferences().unregisterOnSharedPreferenceChangeListener(this);    
    }
  
    // When the user changes the preferences selection, 
    // onSharedPreferenceChanged() restarts the main activity as a new
    // task. Sets the the refreshDisplay flag to "true" to indicate that 
    // the main activity should update its display.
    // The main activity queries the PreferenceManager to get the latest settings.
    
    @Override
    publicvoid onSharedPreferenceChanged(SharedPreferences sharedPreferences,String key){    
        // Sets refreshDisplay to true so that when the user returns to the main
        // activity, the display refreshes to reflect the new settings.
        NetworkActivity.refreshDisplay =true;
    }}

 

Respond to Preference Changes [对偏好改变进行响应]

  • 当用户在设置界面改变了偏好，它通常都会对app的行为产生影响。
  • 在下面的代码示例中，app会在onStart(). 方法里面检查偏好设置。如果设置的类型与当前设备的网络连接类型相一致，那么程序就会下载数据并刷新显示。(for example, if the setting is "Wi-Fi" and the device has a Wi-Fi connection)。[这是一个很好的代码示例，如何选择合适的网络类型进行下载操作]
publicclassNetworkActivityextendsActivity{
    publicstaticfinalString WIFI ="Wi-Fi";
    publicstaticfinalString ANY ="Any";
    privatestaticfinalString URL ="http://stackoverflow.com/feeds/tag?tagnames=android&sort=newest";
   
    // Whether there is a Wi-Fi connection.
    privatestaticboolean wifiConnected =false; 
    // Whether there is a mobile connection.
    privatestaticboolean mobileConnected =false;
    // Whether the display should be refreshed.
    publicstaticboolean refreshDisplay =true;
    
    // The user's current network preference setting.
    publicstaticString sPref =null;
    
    // The BroadcastReceiver that tracks network connectivity changes.
    privateNetworkReceiver receiver =newNetworkReceiver();
    
    @Override
    publicvoid onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        
        // Registers BroadcastReceiver to track network connection changes.
        IntentFilter filter =newIntentFilter(ConnectivityManager.CONNECTIVITY_ACTION);
        receiver =newNetworkReceiver();
        this.registerReceiver(receiver, filter);
    }
    
    @Override 
    publicvoid onDestroy(){
        super.onDestroy();
        // Unregisters BroadcastReceiver when app is destroyed.
        if(receiver !=null){
            this.unregisterReceiver(receiver);
        }
    }
    
    // Refreshes the display if the network connection and the
    // pref settings allow it.
    
    @Override
    publicvoid onStart (){
        super.onStart();  
        
        // Gets the user's network preference settings
        SharedPreferences sharedPrefs =PreferenceManager.getDefaultSharedPreferences(this);
        
        // Retrieves a string value for the preferences. The second parameter
        // is the default value to use if a preference value is not found.
        sPref = sharedPrefs.getString("listPref","Wi-Fi");

        updateConnectedFlags(); 
       
        if(refreshDisplay){
            loadPage();    
        }
    }
    
    // Checks the network connection and sets the wifiConnected and mobileConnected
    // variables accordingly. 
    publicvoid updateConnectedFlags(){
        ConnectivityManager connMgr =(ConnectivityManager) 
                getSystemService(Context.CONNECTIVITY_SERVICE);
        
        NetworkInfo activeInfo = connMgr.getActiveNetworkInfo();
        if(activeInfo !=null&& activeInfo.isConnected()){
            wifiConnected = activeInfo.getType()==ConnectivityManager.TYPE_WIFI;
            mobileConnected = activeInfo.getType()==ConnectivityManager.TYPE_MOBILE;
        }else{
            wifiConnected =false;
            mobileConnected =false;
        }  
    }
      
    // Uses AsyncTask subclass to download the XML feed from stackoverflow.com.
    publicvoid loadPage(){
        if(((sPref.equals(ANY))&&(wifiConnected || mobileConnected))
                ||((sPref.equals(WIFI))&&(wifiConnected))){
            // AsyncTask subclass
            newDownloadXmlTask().execute(URL);
        }else{
            showErrorPage();
        }
    }...
    
}

Detect Connection Changes [监测网络连接的改变]

 

 

  • 最后一部分是关于 BroadcastReceiver 的子类： NetworkReceiver. 当设备网络连接改变时，NetworkReceiver会监听到 CONNECTIVITY_ACTION, 这时需要判断当前网络连接类型并相应的设置好 wifiConnected 与 mobileConnected . 
  • 我们需要控制好BroadcastReceiver的使用，不必要的声明注册会浪费系统资源。通常是在 onCreate() 去registers 这个BroadcastReceiver ， 在onPause()或者onDestroy() 时unregisters它。这样做会比直接在manifest里面直接注册 <receiver> 更轻量. 当你在manifest里面注册了一个 <receiver> ，你的程序可以在任何时候被唤醒, 即使你已经好几个星期没有使用这个程序了。而通过前面的办法进行注册，可以确保用户离开你的程序之后，不会因为那个Broadcast而被唤起。如果你确保知道何时需要使用到它，你可以在合适的地方使用 setComponentEnabledSetting() 来开启或者关闭它。
publicclassNetworkReceiverextendsBroadcastReceiver{   
      
@Overridepublicvoid onReceive(Context context,Intent intent){
    ConnectivityManager conn =  (ConnectivityManager)
        context.getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo networkInfo = conn.getActiveNetworkInfo();
       
    // Checks the user prefs and the network connection. Based on the result, decides whether
    // to refresh the display or keep the current display.
    // If the userpref is Wi-Fi only, checks to see if the device has a Wi-Fi connection.
    if(WIFI.equals(sPref)&& networkInfo !=null&& networkInfo.getType()==ConnectivityManager.TYPE_WIFI){
        // If device has its Wi-Fi connection, sets refreshDisplay
        // to true. This causes the display to be refreshed when the user
        // returns to the app.
        refreshDisplay =true;
        Toast.makeText(context, R.string.wifi_connected,Toast.LENGTH_SHORT).show();

    // If the setting is ANY network and there is a network connection
    // (which by process of elimination would be mobile), sets refreshDisplay to true.
    }elseif(ANY.equals(sPref)&& networkInfo !=null){
        refreshDisplay =true;
                 
    // Otherwise, the app can't download content--either because there is no network
    // connection (mobile or Wi-Fi), or because the pref setting is WIFI, and there 
    // is no Wi-Fi connection.
    // Sets refreshDisplay to false.
    }else{
        refreshDisplay =false;
        Toast.makeText(context, R.string.lost_connection,Toast.LENGTH_SHORT).show();
    }}

 

 

 

学习自：http://developer.android.com/training/basics/network-ops/managing.html，请多指教，谢谢！

转载请注明作者与出自：http://blog.csdn.net/kesenhoo，谢谢配合！

posted @ 2012-06-04 17:56  YangWu-Sky  阅读(314)  评论(0)    收藏  举报