在执行代码之前检查是否存在互联网连接

Question

我想知道在执行某些代码之前是否有一种简单的方法可以检查用户是否有可用的互联网连接。

我想知道这一点，因为如果我没有启用我的互联网连接然后点击“Setwallpaper”，应用程序崩溃是因为“Nullpointerexception”因为没有任何东西可以执行。

在打开下载并设置壁纸的Async任务类之前，如何检查用户是否启用了互联网连接？

代码：

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {

    case R.id.SetWallpaper:

//Do something here that checks if the user has connection so if they don't, it won't execute this code here.

        new SaveWallpaperAsync(getActivity()).execute(mImageUrl);

        break;

    case R.id.SaveWallpaper:

//Do something here that checks if the user has connection so if they don't, it won't execute this code here.

        new SetWallpaperAsync(getActivity()).execute(mImageUrl);

        break;
    }
    return super.onOptionsItemSelected(item);
} 

Answer 1

您需要在oncreate（）或onStart（）

中编写以下代码

    CheckConnection ch = new CheckConnection();
    boolean status = ch.isNetworkAvailable(getApplicationContext());

    if (status) {

        //do Async task





    } else {
        // show error
    }


       public class CheckConnection {

    public boolean isNetworkAvailable(Context context) {            
        ConnectivityManager connectivity = (ConnectivityManager) context.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) {                            
                        return true;
                    }
                }
            }
        }
        return false;
    }

}

Answer 2

使用此方法

public static boolean checkInternetConnection(Context context)
{
    try
    {
        ConnectivityManager conMgr = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);

        // ARE WE CONNECTED TO THE NET

        if (conMgr.getActiveNetworkInfo() != null && conMgr.getActiveNetworkInfo().isAvailable() && conMgr.getActiveNetworkInfo().isConnected())
        {
            return true;
        }
        else
        {
            return false;
        }
    }
    catch (Exception e)
    {
        e.printStackTrace();
    }

    return false;
}

并添加权限

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

清单文件中的

Answer 3

试试如下：

public static boolean IsNetConnected() {
    boolean NetConnected = false;

    try {
        ConnectivityManager connectivity = (ConnectivityManager) m_context
                .getSystemService(m_context.CONNECTIVITY_SERVICE);

        if (connectivity == null) {
            NetConnected = false;
        } else {
            NetworkInfo[] info = connectivity.getAllNetworkInfo();

            if (info != null) {
                for (int i = 0; i < info.length; i++) {
                    if (info[i].getState() == NetworkInfo.State.CONNECTED) {
                        NetConnected = true;
                    }
                }
            }
        }
    } catch (Exception e) {
        e.printStackTrace();
        NetConnected = false;
    }

    return NetConnected;
}

并在清单中添加权限。

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

在您的代码中执行以下操作：

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {

    case R.id.SetWallpaper:

//Do something here that checks if the user has connection so if they don't, it won't execute this code here.
        if( IsNetConnected())
        {
            new SaveWallpaperAsync(getActivity()).execute(mImageUrl);
         }
        break;

    case R.id.SaveWallpaper:

//Do something here that checks if the user has connection so if they don't, it won't execute this code here.
        if( IsNetConnected())
        {
            new SetWallpaperAsync(getActivity()).execute(mImageUrl);
          }
        break;
    }
    return super.onOptionsItemSelected(item);
} 

Answer 4

这就是我的表现。在您要检查互联网连接的活动中的onCreate()中写下以下代码：

        NetworkConnectivity.sharedNetworkConnectivity().configure(this); 
        NetworkConnectivity.sharedNetworkConnectivity().startNetworkMonitor(); 
        NetworkConnectivity.sharedNetworkConnectivity() 
                .addNetworkMonitorListener(new NetworkMonitorListener() { 
                    @Override
                    public void connectionCheckInProgress() { 
                        // Okay to make UI updates (check-in-progress is rare) 
                    } 

                    @Override
                    public void connectionEstablished() { 
                        // Okay to make UI updates -- do something now that 
                        // connection is avaialble 


                    } 

                    @Override
                    public void connectionLost() { 
                        // Okay to make UI updates -- bummer, no connection 

                        Toast.makeText(getBaseContext(), "Connection lost. You cannot use Voice Input method.", Toast.LENGTH_LONG).show(); 


                    } 
                }); 

创建两个java文件：

<强> NetworkConnectivity.java

package com.connectivity; 

import java.util.ArrayList; 
import java.util.List; 

import android.app.Activity; 
import android.content.Context; 
import android.net.ConnectivityManager; 
import android.net.NetworkInfo; 
import android.os.Handler; 

public class NetworkConnectivity { 

    private static NetworkConnectivity sharedNetworkConnectivity = null; 

    private Activity activity = null; 

    private final Handler handler = new Handler(); 
    private Runnable runnable = null; 

    private boolean stopRequested = false; 
    private boolean monitorStarted = false; 

    private static final int NETWORK_CONNECTION_YES = 1; 
    private static final int NETWORK_CONNECTION_NO = -1; 
    private static final int NETWORK_CONNECTION_UKNOWN = 0; 

    private int connected = NETWORK_CONNECTION_UKNOWN; 

    public static final int MONITOR_RATE_WHEN_CONNECTED_MS = 5000; 
    public static final int MONITOR_RATE_WHEN_DISCONNECTED_MS = 1000; 

    private final List<NetworkMonitorListener> networkMonitorListeners = new ArrayList<NetworkMonitorListener>(); 

    private NetworkConnectivity() { 
    } 

    public synchronized static NetworkConnectivity sharedNetworkConnectivity() { 
        if (sharedNetworkConnectivity == null) { 
            sharedNetworkConnectivity = new NetworkConnectivity(); 
        } 

        return sharedNetworkConnectivity; 
    } 

    public void configure(Activity activity) { 
        this.activity = activity; 
    } 

    public synchronized boolean startNetworkMonitor() { 
        if (this.activity == null) { 
            return false; 
        } 

        if (monitorStarted) { 
            return true; 
        } 

        stopRequested = false; 
        monitorStarted = true; 

        (new Thread(new Runnable() { 
            @Override
            public void run() { 
                doCheckConnection(); 
            } 
        })).start(); 

        return true; 
    } 

    public synchronized void stopNetworkMonitor() { 
        stopRequested = true; 
        monitorStarted = false; 
    } 

    public void addNetworkMonitorListener(NetworkMonitorListener l) { 
        this.networkMonitorListeners.add(l); 
        this.notifyNetworkMonitorListener(l); 
    } 

    public boolean removeNetworkMonitorListener(NetworkMonitorListener l) { 
        return this.networkMonitorListeners.remove(l); 
    } 

    private void doCheckConnection() { 

        if (stopRequested) { 
            runnable = null; 
            return; 
        } 

        final boolean connectedBool = this.isConnected(); 
        final int _connected = (connectedBool ? NETWORK_CONNECTION_YES 
                : NETWORK_CONNECTION_NO); 

        if (this.connected != _connected) { 

            this.connected = _connected; 

            activity.runOnUiThread(new Runnable() { 
                @Override
                public void run() { 
                    notifyNetworkMonitorListeners(); 
                } 
            }); 
        } 

        runnable = new Runnable() { 
            @Override
            public void run() { 
                doCheckConnection(); 
            } 
        }; 

        handler.postDelayed(runnable, 
                (connectedBool ? MONITOR_RATE_WHEN_CONNECTED_MS 
                        : MONITOR_RATE_WHEN_DISCONNECTED_MS)); 
    } 

    public boolean isConnected() { 
        try { 
            ConnectivityManager cm = (ConnectivityManager) activity 
                    .getSystemService(Context.CONNECTIVITY_SERVICE); 
            NetworkInfo netInfo = cm.getActiveNetworkInfo(); 

            if (netInfo != null && netInfo.isConnected()) { 
                return true; 
            } else { 
                return false; 
            } 
        } catch (Exception e) { 
            return false; 
        } 
    } 

    private void notifyNetworkMonitorListener(NetworkMonitorListener l) { 
        try { 
            if (this.connected == NETWORK_CONNECTION_YES) { 
                l.connectionEstablished(); 
            } else if (this.connected == NETWORK_CONNECTION_NO) { 
                l.connectionLost(); 
            } else { 
                l.connectionCheckInProgress(); 
            } 
        } catch (Exception e) { 
        } 
    } 

    private void notifyNetworkMonitorListeners() { 
        for (NetworkMonitorListener l : this.networkMonitorListeners) { 
            this.notifyNetworkMonitorListener(l); 
        } 
    } 

} 

<强> NetworkMonitorListener.java

package com.connectivity; 

public interface NetworkMonitorListener { 

    public void connectionEstablished(); 
    public void connectionLost(); 
    public void connectionCheckInProgress(); 
} 

最后，在manifest.xml：

中添加这两行

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

Answer 5

    public static boolean isInternetAvailable(Context ctx) {
            ConnectivityManager cm = (ConnectivityManager) ctx
                    .getSystemService(Context.CONNECTIVITY_SERVICE);
            NetworkInfo netInfo = cm.getActiveNetworkInfo();
            if (netInfo != null && netInfo.isConnectedOrConnecting()
                    && cm.getActiveNetworkInfo().isAvailable()
                    && cm.getActiveNetworkInfo().isConnected()) {
                return true;
            } else {
                return false;
            }
        }
public static void showNetworkAlertDialog(Context mCtx) {
    AlertDialog.Builder builder = new AlertDialog.Builder(mCtx);
    builder.setCancelable(false);
    builder.setTitle("Network Error");
    builder.setMessage("Internet is not available !!");
    builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {

        @Override
        public void onClick(DialogInterface dialog, int which) {
            dialog.dismiss();
        }
    });
    builder.create().show();
}

//比

   if(isInternetAvailable){
    // Execute code here
    }else{
   NetworkUtils.showNetworkAlertDialog(mContext);
    }

//清单

中的权限

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