Question

我在Android应用程序中使用Sherlock侧导航片段。但是，我使用的是6个片段，其中包含带有进度条的webview。

这是其中一个片段：

@SuppressLint("SetJavaScriptEnabled")
public class Fragment1 extends SherlockFragment {
    private WebView mWebview;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
        super.onCreateView(inflater, container, savedInstanceState);
        setHasOptionsMenu(true);

        View rootView = inflater.inflate(R.layout.fragment1, container, false);
        mWebview = (WebView) rootView.findViewById(R.id.webView1);

        mWebview.setInitialScale(1);
        mWebview.getSettings().setJavaScriptEnabled(true);



        mWebview.setWebChromeClient(new WebChromeClient() {
             public void onProgressChanged(WebView view, int progress)   
             {
                   //Make the bar disappear after URL is loaded, and changes string to Loading...
                   getActivity().setTitle("Loading...");
                   getActivity().setProgress(progress * 100); //Make the bar disappear after URL is loaded

                   // Return the app name after finish loading
                   if(progress == 100)
                   getActivity().setTitle(R.string.Fragment1);
                 }

             });


        mWebview.setWebViewClient(new WebViewClient() {
            public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
                //Toast.makeText(activity, description, Toast.LENGTH_SHORT).show();
            }
        });

        mWebview.loadUrl("http://www.LINK");
        WebSettings zoomenable = mWebview.getSettings();
        zoomenable.setBuiltInZoomControls(true);
        WebSettings wideviewenable  = mWebview.getSettings();
        wideviewenable.setUseWideViewPort(true);

        mWebview.setDownloadListener(new DownloadListener() {
            public void onDownloadStart(String url, String userAgent,
                    String contentDisposition, String mimetype,
                    long contentLength) {
              Intent i = new Intent(Intent.ACTION_VIEW);
              i.setData(Uri.parse(url));
              startActivity(i);
            }
        });

        mWebview.setOnKeyListener(new OnKeyListener()
        {
            @Override
            public boolean onKey(View v, int keyCode, KeyEvent event)
            {
             if(mWebview.canGoBack())
             {
             mWebview.goBack();
             return true;
             }

             return false;
            }
        });


        return rootView;
    }

    public class HelloWebViewClient extends WebViewClient {

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

    }

    @Override
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        inflater.inflate(R.menu.main_activity_actions, menu);
        super.onCreateOptionsMenu(menu, inflater);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle presses on the action bar items
        switch (item.getItemId()) {
            case R.id.action_search:
                mWebview.reload();
                return true;
            default:return super.onOptionsItemSelected(item);
        }
    }


}

我面临的问题是，当选择侧面导航中的一个链接并且进度条尚未完成时，它会在onProgressChanged方法中给出空指针异常。

在主要活动中，我使用这两行代码来启用进度条：

this.getWindow().requestFeature(Window.FEATURE_PROGRESS);
this.getWindow().setFeatureInt( Window.FEATURE_PROGRESS, Window.PROGRESS_VISIBILITY_ON);

这是日志猫错误：

05-23 18:54:20.687: E/AndroidRuntime(20112): FATAL EXCEPTION: main
05-23 18:54:20.687: E/AndroidRuntime(20112): java.lang.NullPointerException
05-23 18:54:20.687: E/AndroidRuntime(20112):    at petra.app.Fragment1$1.onProgressChanged(Fragment1.java:45)
05-23 18:54:20.687: E/AndroidRuntime(20112):    at android.webkit.CallbackProxy.handleMessage(CallbackProxy.java:533)
05-23 18:54:20.687: E/AndroidRuntime(20112):    at android.os.Handler.dispatchMessage(Handler.java:99)
05-23 18:54:20.687: E/AndroidRuntime(20112):    at android.os.Looper.loop(Looper.java:137)
05-23 18:54:20.687: E/AndroidRuntime(20112):    at android.app.ActivityThread.main(ActivityThread.java:5297)
05-23 18:54:20.687: E/AndroidRuntime(20112):    at java.lang.reflect.Method.invokeNative(Native Method)
05-23 18:54:20.687: E/AndroidRuntime(20112):    at java.lang.reflect.Method.invoke(Method.java:511)
05-23 18:54:20.687: E/AndroidRuntime(20112):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
05-23 18:54:20.687: E/AndroidRuntime(20112):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
05-23 18:54:20.687: E/AndroidRuntime(20112):    at dalvik.system.NativeStart.main(Native Method)

提前致谢。

Answer 1

好吧，我几乎可以肯定，当活动不再可见时，当WebChromeClient发布的porgress被触发时，就会发生这种情况。

你应该检查“getActivity（）”调用是否返回null，并且......

要对您的代码应用更正，请查看以下内容：

mWebview.setWebChromeClient(new WebChromeClient() {
         public void onProgressChanged(WebView view, int progress)   
         {
              // here you check the value of getActivity() and break up if needed
             if(getActivity() == null)
                 return;

               //Make the bar disappear after URL is loaded, and changes string to Loading...
               getActivity().setTitle("Loading...");
               getActivity().setProgress(progress * 100); //Make the bar disappear after URL is loaded

               // Return the app name after finish loading
               if(progress == 100)
               getActivity().setTitle(R.string.Fragment1);
             }

         });

Answer 2

您可以尝试以下代码：

    mWebview.setWebChromeClient(new WebChromeClient() {
         public void onProgressChanged(WebView view, int progress)   
         {
               //Make the bar disappear after URL is loaded, and changes string to Loading...
               Activity activity = getActivity();
               if (activity != null) {
                  activity.setTitle("Loading...");
                  activity.setProgress(progress * 100); //Make the bar disappear after URL is loaded
                  // Return the app name after finish loading
                  if(progress == 100)
                  activity.setTitle(R.string.Fragment1);
                }
             }
         });

在Fragment中使用onProgressChanged时出现空指针异常

2 个答案: