在Android Webview中以離線模式加載緩存

Question

我發現了一個代碼，用於檢查應用程序是否處於脫機狀態，並且必須加載緩存，或者處於在線模式下並且必須加載url。這是我用的代碼：

ConnectivityManager cm = (ConnectivityManager) this.getSystemService(Activity.CONNECTIVITY_SERVICE); 
String weblink = "http://www.google.com"; 
if(cm.getActiveNetworkInfo().isConnected()){ 
    myWebView.getSettings().setCacheMode(WebSettings.LOAD_DEFAULT); 
    myWebView.loadUrl(weblink); 
} else { 
    myWebView.getSettings().setCacheMode(WebSettings.LOAD_CACHE_ELSE_NETWORK); 
    myWebView.loadUrl(weblink); 
} 

這些都是我的權限：

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

我的問題：當我在飛行模式或我的連接關閉。應用程序部隊關閉。當我在線時，該應用只是加載並正常運行......我錯了什麼？

這是我的logcat：

11-22 10:09:40.310: E/AndroidRuntime(323): FATAL EXCEPTION: main 
11-22 10:09:40.310: E/AndroidRuntime(323): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.martijngijselaar.rooster/com.martijngijselaar.rooster.SaxionRoosterActivity}: java.lang.NullPointerException 
11-22 10:09:40.310: E/AndroidRuntime(323): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663) 
11-22 10:09:40.310: E/AndroidRuntime(323): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679) 
11-22 10:09:40.310: E/AndroidRuntime(323): at android.app.ActivityThread.access$2300(ActivityThread.java:125) 
11-22 10:09:40.310: E/AndroidRuntime(323): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033) 
11-22 10:09:40.310: E/AndroidRuntime(323): at android.os.Handler.dispatchMessage(Handler.java:99) 
11-22 10:09:40.310: E/AndroidRuntime(323): at android.os.Looper.loop(Looper.java:123) 
11-22 10:09:40.310: E/AndroidRuntime(323): at android.app.ActivityThread.main(ActivityThread.java:4627) 
11-22 10:09:40.310: E/AndroidRuntime(323): at java.lang.reflect.Method.invokeNative(Native Method) 
11-22 10:09:40.310: E/AndroidRuntime(323): at java.lang.reflect.Method.invoke(Method.java:521) 
11-22 10:09:40.310: E/AndroidRuntime(323): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 
11-22 10:09:40.310: E/AndroidRuntime(323): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 
11-22 10:09:40.310: E/AndroidRuntime(323): at dalvik.system.NativeStart.main(Native Method) 
11-22 10:09:40.310: E/AndroidRuntime(323): Caused by: java.lang.NullPointerException 
11-22 10:09:40.310: E/AndroidRuntime(323): at com.martijngijselaar.rooster.SaxionRoosterActivity.onCreate(SaxionRoosterActivity.java:34) 
11-22 10:09:40.310: E/AndroidRuntime(323): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
11-22 10:09:40.310: E/AndroidRuntime(323): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627) 
11-22 10:09:40.310: E/AndroidRuntime(323): ... 11 more 

好，使之更容易在這裏是整個代碼：需要進行調整

package com.martijngijselaar.rooster; 

import android.app.Activity; 
import android.net.ConnectivityManager; 
import android.os.Bundle; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.MotionEvent; 
import android.view.View; 
import android.view.Window; 
import android.webkit.WebSettings; 
import android.webkit.WebView; 
import android.webkit.WebViewClient; 

public class SaxionRoosterActivity extends Activity { 
    private static final int MENU1 = Menu.FIRST; 
    private static final int MENU2 = Menu.FIRST + 1; 
    private static final int MENU3 = Menu.FIRST + 2; 

    /** Called when the activity is first created. */ 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     this.requestWindowFeature(Window.FEATURE_NO_TITLE); 

     setContentView(R.layout.main); 
     WebView myWebView = (WebView) findViewById(R.id.webview); 
     myWebView.setWebViewClient(new WebViewClient()); 

     // Checken of er een connectie is, zo niet dan de chache laden, zo wel dan gewoon het netwerk laden!! 
     ConnectivityManager cm = (ConnectivityManager) this.getSystemService(Activity.CONNECTIVITY_SERVICE); 
     String weblink = "http://google.com/"; 
     if(cm.getActiveNetworkInfo().isConnected()){ 
      myWebView.getSettings().setCacheMode(WebSettings.LOAD_DEFAULT); 
      myWebView.loadUrl(weblink); 
     } else { 
      myWebView.getSettings().setCacheMode(WebSettings.LOAD_CACHE_ELSE_NETWORK); 
      myWebView.loadUrl(weblink); 
     } 

     // Zorgen dat je input kunt gebruiken in de webview 
     myWebView.requestFocus(View.FOCUS_DOWN); 
     myWebView.setOnTouchListener(new View.OnTouchListener() { 
      public boolean onTouch(View v, MotionEvent event) { 
       switch (event.getAction()) { 
        case MotionEvent.ACTION_DOWN: 
        case MotionEvent.ACTION_UP: 
         if (!v.hasFocus()) { 
          v.requestFocus(); 
         } 
         break; 
       } 
       return false; 
      } 

     }); 
    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     menu.add(0, MENU1, 0, "Wijzig klas"); 
     menu.add(0, MENU2, 0, "Disclaimer"); 
     menu.add(0, MENU3, 0, "Sluiten"); 
     return true; 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
     WebView myWebView = (WebView) findViewById(R.id.webview); 
     switch (item.getItemId()) { 
     case MENU1: 
      myWebView.loadUrl("http://google.nl"); 
      return true; 
     case MENU2: 
      myWebView.loadUrl("http://google.nl"); 
      return true; 
     case MENU3: 
      finish(); 
      return true; 
     } 
     return false; 
    } 
} 

Answer 1

您的連接檢查。雖然有一個名爲isConnected的屬性，但您首先需要檢查getActiveNetworkInfo（）是否返回null。如果它返回空值，則沒有活動的網絡信息 - 這是你在飛行模式下得到的。 這是我用於網絡連接的檢查

private boolean isNetworkAvailable() { 
    ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE); 
    NetworkInfo activeNetworkInfo = connectivityManager.getActiveNetworkInfo(); 
    return activeNetworkInfo != null; 
}