Android WebApp强制关闭后退按钮

Question

I have a web app I'm making to run off a CMS that is using jQuery Mobile to make mobile compatible page versions. The base log in page is stored locally on the phone.

public class WebAppActivity extends Activity {
WebView webView;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    this.getWindow().requestFeature(Window.FEATURE_PROGRESS);
    this.requestWindowFeature(Window.FEATURE_NO_TITLE);

    // Point to the content view defined in XML

    setContentView(R.layout.main);

    // Configure the webview setup in the xml layout

    WebView webView = (WebView) findViewById(R.id.webView1);

    WebSettings webSettings = webView.getSettings();

    // Yes, we want javascript, pls.

    webSettings.setJavaScriptEnabled(true);


    webView.loadUrl("file:///android_asset/www/webapp.html");



webView.setWebViewClient(new WebViewClient() { 
    @Override
     public boolean shouldOverrideUrlLoading(WebView view, String url){
         view.loadUrl(url);
         return true;
     }
 });


}



@Override
 public void onBackPressed()
{
    if(webView.canGoBack())
    {
        webView.goBack();
    }else{
        super.onBackPressed();
    }
}

}

and the the Logcat says :

03-29 15:31:47.354: E/AndroidRuntime(430): FATAL EXCEPTION: main
03-29 15:31:47.354: E/AndroidRuntime(430): java.lang.NullPointerException
03-29 15:31:47.354: E/AndroidRuntime(430):  at com.package.mobile.android.webapp.onBackPressed(WebApp.java:223)
03-29 15:31:47.354: E/AndroidRuntime(430):  at android.app.Activity.onKeyUp(Activity.java:1898)
03-29 15:31:47.354: E/AndroidRuntime(430):  at android.view.KeyEvent.dispatch(KeyEvent.java:1280)
03-29 15:31:47.354: E/AndroidRuntime(430):  at android.app.Activity.dispatchKeyEvent(Activity.java:2078)
03-29 15:31:47.354: E/AndroidRuntime(430):  at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:1663)
03-29 15:31:47.354: E/AndroidRuntime(430):  at android.view.ViewRoot.deliverKeyEventToViewHierarchy(ViewRoot.java:2560)
03-29 15:31:47.354: E/AndroidRuntime(430):  at android.view.ViewRoot.handleFinishedEvent(ViewRoot.java:2535)
03-29 15:31:47.354: E/AndroidRuntime(430):  at android.view.ViewRoot.handleMessage(ViewRoot.java:1867)
03-29 15:31:47.354: E/AndroidRuntime(430):  at android.os.Handler.dispatchMessage(Handler.java:99)
03-29 15:31:47.354: E/AndroidRuntime(430):  at android.os.Looper.loop(Looper.java:123)
03-29 15:31:47.354: E/AndroidRuntime(430):  at android.app.ActivityThread.main(ActivityThread.java:3683)
03-29 15:31:47.354: E/AndroidRuntime(430):  at java.lang.reflect.Method.invokeNative(Native Method)
03-29 15:31:47.354: E/AndroidRuntime(430):  at java.lang.reflect.Method.invoke(Method.java:507)
03-29 15:31:47.354: E/AndroidRuntime(430):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
03-29 15:31:47.354: E/AndroidRuntime(430):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
03-29 15:31:47.354: E/AndroidRuntime(430):  at dalvik.system.NativeStart.main(Native Method)

I've been trying to get around this for the past week or so, it seems as if the webview isn't building a history to go back through.

Answer 1

try this :

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

Answer 2

The NullPointerException is because your webView is a local variable in onCreate , and the webView class member variable is left unassigned.

Off-topic: I won't go into a long tirade about purely WebView-based apps, but let's just say you shouldn't do it. And if you absolutely have to for some reason or another, then you should make sure to handle orientation changes.

Answer 3

you need to override the backbutton default behaviour, this is achieved by

       @Override
public void onBackPressed() {

    return;
}

in the main activity of your application

Answer 4

按下后退按钮你应该拨打电话

finish();