根据我的 Internet 连接状态更改 setContentView 的布局

Question

我目前正在开发一个应用程序，我想在其中添加一项功能。当没有互联网时，活动的布局必须反之亦然。我在 android 方面不太好，我用这段代码来做我的小想法。任何想法如何实现这一点。当我尝试应用程序崩溃时。

public class RescuingActivity extends AppCompatActivity {

private BroadcastReceiver receiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        if(ConnectivityStatus.isConnected(getContext())){
            setContentView(R.layout.rescue_page);
        }else {
            setContentView(R.layout.no_connection);
        }
    }
};

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    getContext().registerReceiver(receiver, new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION));
    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
    mapFragment.getMapAsync(this);
 }
}

Logcat 错误：

xxx/E/AndroidRuntime: 致命异常: main 进程：xxx，PID：6258 java.lang.RuntimeException：无法启动活动 ComponentInfo{xxx.xxx.xxxxxxx/xxx.xxx.xxxxxxx.view.RescuingActivity}：java.lang.NullPointerException 在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2221) 在 android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2280) 在 android.app.ActivityThread.access$800(ActivityThread.java:141) 在 android.app.ActivityThread$H.handleMessage(ActivityThread.java:1202) 在 android.os.Handler.dispatchMessage(Handler.java:102) 在 android.os.Looper.loop(Looper.java:136) 在 android.app.ActivityThread.main(ActivityThread.java:5059) 在 java.lang.reflect.Method.invokeNative(Native Method) 在 java.lang.reflect.Method.invoke(Method.java:515) 在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785) 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601) 在 dalvik.system.NativeStart.main（本机方法） 引起：java.lang.NullPointerException 在 com.kit.arescue.view.RescuingActivity.onCreate(RescuingActivity.java:90)

Answer 1

试试这个功能

    public boolean isConnectingToInternet(){
    ConnectivityManager connectivity = (ConnectivityManager) Login_Page.this.getSystemService(Context.CONNECTIVITY_SERVICE);
      if (connectivity != null)
      {
          NetworkInfo[] info = connectivity.getAllNetworkInfo();
          if (info != null)
              for (int i = 0; i < info.length; i++)
                  if (info[i].getState() == NetworkInfo.State.CONNECTED)
                  {
                      try
                        {
                            HttpURLConnection urlc = (HttpURLConnection) (new URL("http://www.google.com").openConnection());
                            urlc.setRequestProperty("User-Agent", "Test");
                            urlc.setRequestProperty("Connection", "close");
                            urlc.setConnectTimeout(500); //choose your own timeframe
                            urlc.setReadTimeout(500); //choose your own timeframe
                            urlc.connect();
                            int networkcode2 = urlc.getResponseCode();
                            return (urlc.getResponseCode() == 200);
                        } catch (IOException e)
                        {
                            return (false);  //connectivity exists, but no internet.
                        }
                  }

      }
      return false;
}

别忘了添加权限

<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

Answer 2

找到答案，尝试使用 2 个视图。

 private BroadcastReceiver receiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        if(!ConnectivityStatus.isConnected(getContext())){
            childLayoutRescuingActivity.setVisibility(INVISIBLE);
            childLayoutNoConnection.setVisibility(View.VISIBLE);
        }else {
            childLayoutRescuingActivity.setVisibility(View.VISIBLE);
            childLayoutNoConnection.setVisibility(INVISIBLE);
        }
    }
};