Question

我已经在这方面工作了几天了。我刚开始使用Android。我有两个问题。我想检查互联网是否可用。如果它是启动webView，如果没有发出警报并阻止webView加载。我试过这个，但如果没有互联网连接（例如飞机模式），它会强行关闭。如何让它发送消息并停止加载webview。还有一种方法可以连续检查连接，以便在网页断开连接时不显示网页404？

这是我的代码。

    public class MainActivity extends Activity {

    private WebView webView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
        android.net.NetworkInfo wifi = cm
                .getNetworkInfo(ConnectivityManager.TYPE_WIFI);
        android.net.NetworkInfo datac = cm
                .getNetworkInfo(ConnectivityManager.TYPE_MOBILE);
        if ((wifi != null & datac != null)
                && (wifi.isConnected() | datac.isConnected())) {
            setContentView(R.layout.activity_main);
                 }else{
                //no connection
                  Toast toast = Toast.makeText(MainActivity.this, "No Internet Connection", Toast.LENGTH_LONG);
                  toast.show();  
        }

        CookieManager cookieManager = CookieManager.getInstance(); 
        cookieManager.setAcceptCookie(true); 

        webView = (WebView) findViewById(R.id.webview);
        webView.setWebViewClient(new MyWebViewClient());
        webView.getSettings().setJavaScriptEnabled(true);
        webView.loadUrl("http://mysite.com/?ma=1");
    }   
        private class MyWebViewClient extends WebViewClient {
            @Override
            public boolean shouldOverrideUrlLoading(WebView view, String url) {
                if (Uri.parse(url).getHost().equals("mysite.com")) {
                    return false;
                }
                // Otherwise, the link is not for a page on my site, so launch another Activity that handles URLs
                Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse(url));
                startActivity(intent);
                return true;
            }
        }


    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        // Check if the key event was the Back button and if there's history
        if ((keyCode == KeyEvent.KEYCODE_BACK) && webView.canGoBack()) {
            webView.goBack();
            return true;
        }
        // If it wasn't the Back key or there's no web page history, bubble up to the default
        // system behavior (probably exit the activity)
        return super.onKeyDown(keyCode, event);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) 
    {
        switch (item.getItemId()) 
        {
            case R.id.logout:
                finish();
                return true;
        }
      return false;
    }


}

编辑：添加了错误具体来说，在显示Toast表示没有互联网连接后，按下后会出现这些错误。如果我在toast消息后使用后退按钮并且错误在下面，则崩溃。

04-07 14:40:38.664: E/AndroidRuntime(15173): FATAL EXCEPTION: main
04-07 14:40:38.664: E/AndroidRuntime(15173): java.lang.NullPointerException
04-07 14:40:38.664: E/AndroidRuntime(15173):    at com.mysite.testapp.MainActivity.onKeyDown(MainActivity.java:67)
04-07 14:40:38.664: E/AndroidRuntime(15173):    at android.view.KeyEvent.dispatch(KeyEvent.java:2705)
04-07 14:40:38.664: E/AndroidRuntime(15173):    at android.app.Activity.dispatchKeyEvent(Activity.java:2401)
04-07 14:40:38.664: E/AndroidRuntime(15173):    at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:2007)
04-07 14:40:38.664: E/AndroidRuntime(15173):    at android.view.ViewRootImpl.deliverKeyEventPostIme(ViewRootImpl.java:3813)
04-07 14:40:38.664: E/AndroidRuntime(15173):    at android.view.ViewRootImpl.handleImeFinishedEvent(ViewRootImpl.java:3761)
04-07 14:40:38.664: E/AndroidRuntime(15173):    at android.view.ViewRootImpl$ViewRootHandler.handleMessage(ViewRootImpl.java:2926)
04-07 14:40:38.664: E/AndroidRuntime(15173):    at android.os.Handler.dispatchMessage(Handler.java:99)
04-07 14:40:38.664: E/AndroidRuntime(15173):    at android.os.Looper.loop(Looper.java:137)
04-07 14:40:38.664: E/AndroidRuntime(15173):    at android.app.ActivityThread.main(ActivityThread.java:4918)
04-07 14:40:38.664: E/AndroidRuntime(15173):    at java.lang.reflect.Method.invokeNative(Native Method)
04-07 14:40:38.664: E/AndroidRuntime(15173):    at java.lang.reflect.Method.invoke(Method.java:511)
04-07 14:40:38.664: E/AndroidRuntime(15173):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1004)
04-07 14:40:38.664: E/AndroidRuntime(15173):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:771)
04-07 14:40:38.664: E/AndroidRuntime(15173):    at dalvik.system.NativeStart.main(Native Method)

Answer 1

要检查网络连接可用性，请使用以下

    public class CheckNetwork {


private static final String TAG = CheckNetwork.class.getSimpleName();



public static boolean isInternetAvailable(Context context)
{
    NetworkInfo info = (NetworkInfo) ((ConnectivityManager)
    context.getSystemService(Context.CONNECTIVITY_SERVICE)).getActiveNetworkInfo();

    if (info == null)
    {
         Log.d(TAG,"no internet connection");
         return false;
    }
    else
    {
        if(info.isConnected())
        {
            Log.d(TAG," internet connection available...");
            return true;
        }
        else
        {
            Log.d(TAG," internet connection");
            return true;
        }

    }
}
    }

在您的活动中

              if(CheckNetwork.isInternetAvailable(Activity.this)) //returns true if internet available
                {

                        //do something. loadwebview.
                }   
               else
                {
                    Toast.makeText(Activity.this,"No Internet Connection",1000).show();
                }

按后退按钮

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if(event.getAction() == KeyEvent.ACTION_DOWN){
        switch(keyCode)
        {
        case KeyEvent.KEYCODE_BACK:
            if(mWebView.canGoBack() == true){
                mWebView.goBack();
            }else{
                finish();
            }
            return true;
        }

    }
    return super.onKeyDown(keyCode, event);
   }

更新：如果您需要始终检查网络连接可用性，则系统会在连接发生变化或连接断开时广播事件。您可以通过注册广播来捕获活动中的广播。但是你需要在不需要时取消注册。

以下链接就是一个例子。

Android service to check internet connectivity?

或者您可以使用在后台检查互联网连接的服务。但是，您需要在不需要时销毁服务。但服务用于在后台运行长时间运行的操作

更新2：

尝试以下方法。我测试过了。它适用于我的三星Galaxy S3。

在清单

中添加这些权限

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

您的activity_main.xml

 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:tools="http://schemas.android.com/tools"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 tools:context=".MainActivity" >

 <WebView
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_centerHorizontal="true"
    android:layout_centerVertical="true"
    android:id="@+id/wv"/>

</RelativeLayout>

您的活动

 public class MainActivity extends Activity {

 private WebView webView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);


        setContentView(R.layout.activity_main);
        webView = (WebView) findViewById(R.id.wv);
        if(CheckNetwork.isInternetAvailable(MainActivity.this))
        {
        CookieManager cookieManager = CookieManager.getInstance(); 
        cookieManager.setAcceptCookie(true); 

      // webView = (WebView) findViewById(R.id.wv);
       // webView.setWebViewClient(new MyWebViewClient());
        webView.getSettings().setJavaScriptEnabled(true);
        webView.setWebChromeClient(new WebChromeClient() {
               public void onProgressChanged(WebView view, int progress) {
                 // Activities and WebViews measure progress with different scales.
                 // The progress meter will automatically disappear when we reach 100%
                MainActivity.this.setProgress(progress * 1000);
               }
             });
             webView.setWebViewClient(new WebViewClient() {
               public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
                 Toast.makeText(MainActivity.this, "Oh no! " + description, Toast.LENGTH_SHORT).show();
               }
             });

             webView.loadUrl("http://slashdot.org/");
             }
     else{
            //no connection
              Toast toast = Toast.makeText(MainActivity.this, "No Internet Connection", Toast.LENGTH_LONG);
              toast.show();  
    }


}   



@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if ((keyCode == KeyEvent.KEYCODE_BACK) && webView.canGoBack()) {
        webView.goBack();
        return true;
    }
    else
    {
        finish();
    }
    return super.onKeyDown(keyCode, event);
}
}

Answer 2

为了防止应用程序崩溃，请将定义WebView的所有代码移动到您检查互联网连接的位置，如下所示：

....
if ((wifi != null & datac != null) && (wifi.isConnected() || datac.isConnected())) 
{
    setContentView(R.layout.activity_main);
    webView = (WebView) findViewById(R.id.webview);
    webView.setWebViewClient(new MyWebViewClient());
    webView.getSettings().setJavaScriptEnabled(true);
    webView.loadUrl("http://mysite.com/?ma=1");
}
else
{
   //no connection
    Toast toast = Toast.makeText(MainActivity.this, "No Internet Connection",Toast.LENGTH_LONG);
    toast.show();  
}
.....

现在，如果你的应用程序经常需要互联网连接，我建议你创建一个Service来不断检查这个连接，当它存在时，这个Service会向收听广播方。

<强>更新

由于此行，您收到错误：

webView.goBack();

如果没有互联网连接并且没有实例化WebView，那么你就不能在其中使用goBack（），因为这是null，在这里你需要检查：

if (webView != null)
{
     webView.goBack(); 
}

设置替代视图并不困难： 1.打开可视编辑器，创建一个与webview相同大小的ImageView。 2.然后这样做：

....
if ((wifi != null & datac != null) && (wifi.isConnected() || datac.isConnected())) 
{
    imageView.setVisibility(View.GONE);
    setContentView(R.layout.activity_main);
    webView = (WebView) findViewById(R.id.webview);
    webView.setWebViewClient(new MyWebViewClient());
    webView.getSettings().setJavaScriptEnabled(true);
    webView.loadUrl("http://mysite.com/?ma=1");
}
else
{
   imageView.setVisibility(View.VISIBLE); 
   //no connection
    Toast toast = Toast.makeText(MainActivity.this, "No Internet Connection",Toast.LENGTH_LONG);
    toast.show();  
}
.....

当然，在你可以操作它之前，你必须首先通过id找到这个视图。

Android - 如果没有互联网连接则显示消息并继续检查

2 个答案: