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

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.