我在我的应用程序中添加了一个带有后退、刷新、前进和关于选项的侧面选项菜单，但是每当我单击这些按钮中的任何一个时，我的应用程序都会停止工作，请帮助我。
如果可能，请突出显示错误的代码部分..
代码：
public class MainActivity extends Activity {
WebView myWebView;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//setContentView(R.layout.main);
// Let's display the progress in the activity title bar, like the
// browser app does.
getWindow().requestFeature(Window.FEATURE_PROGRESS);
WebView webview = new WebView(this);
setContentView(webview);
webview.getSettings().setJavaScriptEnabled(true);
webview.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);
}
});
webview.setOnKeyListener(new View.OnKeyListener()
{
@Override
public boolean onKey(View v, int keyCode, KeyEvent event)
{
if(event.getAction() == KeyEvent.ACTION_DOWN)
{
WebView webView = (WebView) v;
switch(keyCode)
{
case KeyEvent.KEYCODE_BACK:
if(webView.canGoBack())
{
webView.goBack();
return true;
}
break;
}
}
return false;
}
});
final Activity activity = this;
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%
activity.setProgress(progress * 1000);
}
});
webview.setWebViewClient(new WebViewClient() {
public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
//Users will be notified in case there's an error (i.e. no internet connection)
Toast.makeText(activity, "Oh no! " + description, Toast.LENGTH_SHORT).show();
}
});
//This will load the webpage that we want to see
webview.loadUrl("http://www.xxxxx.com");
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
super.onCreateOptionsMenu(menu); // Add menu items, second value is the id, use this in the onCreateOptionsMenu
menu.add(0, 1, 0, "Back");
menu.add(0, 2, 0, "Refresh");
menu.add(0, 3, 0, "Forward");
menu.add(0, 4, 0, "About");
return true; // End of menu configuration
}
public boolean onOptionsItemSelected(MenuItem item){ // Called when you tap a menu item
switch (item.getItemId()){
case 1: //If the ID equals 1, go back
if (myWebView.canGoBack()){
myWebView.goBack();
return true;
}
case 2 : //If the ID equals 2, refresh
myWebView.reload();
return true;
case 3: //If the ID equals 3, go forward
if (myWebView.canGoForward()){
myWebView.goForward();
return true;
}
case 4: //aha showing about us
myWebView.loadUrl("http://example.com/about.php");
}
return false;
}
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) { // Enables browsing to previous pages with the hardware back button
WebView webView = new WebView(this);
if ((keyCode == KeyEvent.KEYCODE_BACK) && webView.canGoBack()) { // Check if the key event was the BACK key and if there's history
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);
}
}
这是日志：
08-04 12:38:25.319 37-37/? E/SurfaceFlinger: ro.sf.lcd_density must be defined as a build property
08-04 12:38:28.687 3589-3589/com.example D/AndroidRuntime: Shutting down VM
08-04 12:38:28.687 3589-3589/com.example W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0x40a71930)
08-04 12:38:28.778 3589-3589/com.example E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.NullPointerException
at com.example.MainActivity.onOptionsItemSelected(MainActivity.java:125)
at android.app.Activity.onMenuItemSelected(Activity.java:2548)
at com.android.internal.policy.impl.PhoneWindow.onMenuItemSelected(PhoneWindow.java:980)
at com.android.internal.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:735)
at com.android.internal.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:149)
at com.android.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:874)
at com.android.internal.view.menu.MenuPopupHelper.onItemClick(MenuPopupHelper.java:156)
at android.widget.AdapterView.performItemClick(AdapterView.java:298)
at android.widget.AbsListView.performItemClick(AbsListView.java:1100)
at android.widget.AbsListView$PerformClick.run(AbsListView.java:2749)
at android.widget.AbsListView$1.run(AbsListView.java:3423)
at android.os.Handler.handleCallback(Handler.java:725)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5041)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
at dalvik.system.NativeStart.main(Native Method)
08-04 12:38:28.817 322-542/system_process W/ActivityManager: Force finishing activity com.example/.MainActivity
08-04 12:38:28.837 322-542/system_process W/WindowManager: Failure taking screenshot for (328x583) to layer 21035
08-04 12:38:29.287 37-162/? E/SurfaceFlinger: ro.sf.lcd_density must be defined as a build property
08-04 12:38:29.425 322-337/system_process W/ActivityManager: Activity pause timeout for ActivityRecord{411a3cd0 u0 com.example/.MainActivity}
08-04 12:38:29.747 708-723/com.android.exchange D/ExchangeService: Received deviceId from Email app: null
08-04 12:38:29.747 708-723/com.android.exchange D/ExchangeService: !!! deviceId unknown; stopping self and retrying
08-04 12:38:30.047 457-457/com.android.launcher I/Choreographer: Skipped 35 frames! The application may be doing too much work on its main thread.
08-04 12:38:30.337 37-37/? E/SurfaceFlinger: ro.sf.lcd_density must be defined as a build property
08-04 12:38:34.848 708-724/com.android.exchange D/ExchangeService: !!! EAS ExchangeService, onCreate
08-04 12:38:34.848 708-708/com.android.exchange D/ExchangeService: !!! EAS ExchangeService, onStartCommand, startingUp = false, running = false
08-04 12:38:34.858 322-560/system_process W/ActivityManager: Unable to start service Intent { act=com.android.email.ACCOUNT_INTENT } U=0: not found
08-04 12:38:34.858 708-898/com.android.exchange D/ExchangeService: !!! Email application not found; stopping self
08-04 12:38:34.880 322-669/system_process W/ActivityManager: Unable to start service Intent { act=com.android.email.ACCOUNT_INTENT } U=0: not found
08-04 12:38:34.887 708-708/com.android.exchange D/ExchangeService: !!! EAS ExchangeService, onStartCommand, startingUp = true, running = false
08-04 12:38:34.918 708-708/com.android.exchange E/ActivityThread: Service com.android.exchange.ExchangeService has leaked ServiceConnection com.android.emailcommon.service.ServiceProxy$ProxyConnection@40d4ceb0 that was originally bound here
android.app.ServiceConnectionLeaked: Service com.android.exchange.ExchangeService has leaked ServiceConnection com.android.emailcommon.service.ServiceProxy$ProxyConnection@40d4ceb0 that was originally bound here
at android.app.LoadedApk$ServiceDispatcher.<init>(LoadedApk.java:969)
at android.app.LoadedApk.getServiceDispatcher(LoadedApk.java:863)
at android.app.ContextImpl.bindService(ContextImpl.java:1418)
at android.app.ContextImpl.bindService(ContextImpl.java:1407)
at android.content.ContextWrapper.bindService(ContextWrapper.java:473)
at com.android.emailcommon.service.ServiceProxy.setTask(ServiceProxy.java:157)
at com.android.emailcommon.service.ServiceProxy.setTask(ServiceProxy.java:145)
at com.android.emailcommon.service.AccountServiceProxy.getDeviceId(AccountServiceProxy.java:116)
at com.android.exchange.ExchangeService.getDeviceId(ExchangeService.java:1249)
at com.android.exchange.ExchangeService$7.run(ExchangeService.java:1856)
at com.android.emailcommon.utility.Utility$2.doInBackground(Utility.java:551)
at com.android.emailcommon.utility.Utility$2.doInBackground(Utility.java:549)
at android.os.AsyncTask$2.call(AsyncTask.java:287)
at java.util.concurrent.FutureTask.run(FutureTask.java:234)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
at java.lang.Thread.run(Thread.java:856)
08-04 12:38:35.021 708-708/com.android.exchange E/StrictMode: null
android.app.ServiceConnectionLeaked: Service com.android.exchange.ExchangeService has leaked ServiceConnection com.android.emailcommon.service.ServiceProxy$ProxyConnection@40d4ceb0 that was originally bound here
at android.app.LoadedApk$ServiceDispatcher.<init>(LoadedApk.java:969)
at android.app.LoadedApk.getServiceDispatcher(LoadedApk.java:863)
at android.app.ContextImpl.bindService(ContextImpl.java:1418)
at android.app.ContextImpl.bindService(ContextImpl.java:1407)
at android.content.ContextWrapper.bindService(ContextWrapper.java:473)
at com.android.emailcommon.service.ServiceProxy.setTask(ServiceProxy.java:157)
at com.android.emailcommon.service.ServiceProxy.setTask(ServiceProxy.java:145)
at com.android.emailcommon.service.AccountServiceProxy.getDeviceId(AccountServiceProxy.java:116)
at com.android.exchange.ExchangeService.getDeviceId(ExchangeService.java:1249)
at com.android.exchange.ExchangeService$7.run(ExchangeService.java:1856)
at com.android.emailcommon.utility.Utility$2.doInBackground(Utility.java:551)
at com.android.emailcommon.utility.Utility$2.doInBackground(Utility.java:549)
at android.os.AsyncTask$2.call(AsyncTask.java:287)
at java.util.concurrent.FutureTask.run(FutureTask.java:234)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
at java.lang.Thread.run(Thread.java:856)
08-04 12:38:35.021 322-333/system_process W/ActivityManager: Unbind failed: could not find connection for android.os.BinderProxy@411d8540
08-04 12:38:35.047 708-708/com.android.exchange E/ActivityThread: Service com.android.exchange.ExchangeService has leaked ServiceConnection com.android.emailcommon.service.ServiceProxy$ProxyConnection@40ce0338 that was originally bound here
android.app.ServiceConnectionLeaked: Service com.android.exchange.ExchangeService has leaked ServiceConnection com.android.emailcommon.service.ServiceProxy$ProxyConnection@40ce0338 that was originally bound here
at android.app.LoadedApk$ServiceDispatcher.<init>(LoadedApk.java:969)
at android.app.LoadedApk.getServiceDispatcher(LoadedApk.java:863)
at android.app.ContextImpl.bindService(ContextImpl.java:1418)
at android.app.ContextImpl.bindService(ContextImpl.java:1407)
at android.content.ContextWrapper.bindService(ContextWrapper.java:473)
at com.android.emailcommon.service.ServiceProxy.setTask(ServiceProxy.java:157)
at com.android.emailcommon.service.ServiceProxy.setTask(ServiceProxy.java:145)
at com.android.emailcommon.service.ServiceProxy.test(ServiceProxy.java:191)
at com.android.exchange.ExchangeService$7.run(ExchangeService.java:1850)
at com.android.emailcommon.utility.Utility$2.doInBackground(Utility.java:551)
at com.android.emailcommon.utility.Utility$2.doInBackground(Utility.java:549)
at android.os.AsyncTask$2.call(AsyncTask.java:287)
at java.util.concurrent.FutureTask.run(FutureTask.java:234)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
at java.lang.Thread.run(Thread.java:856)
08-04 12:38:35.047 708-708/com.android.exchange E/StrictMode: null
android.app.ServiceConnectionLeaked: Service com.android.exchange.ExchangeService has leaked ServiceConnection com.android.emailcommon.service.ServiceProxy$ProxyConnection@40ce0338 that was originally bound here
at android.app.LoadedApk$ServiceDispatcher.<init>(LoadedApk.java:969)
at android.app.LoadedApk.getServiceDispatcher(LoadedApk.java:863)
at android.app.ContextImpl.bindService(ContextImpl.java:1418)
at android.app.ContextImpl.bindService(ContextImpl.java:1407)
at android.content.ContextWrapper.bindService(ContextWrapper.java:473)
at com.android.emailcommon.service.ServiceProxy.setTask(ServiceProxy.java:157)
at com.android.emailcommon.service.ServiceProxy.setTask(ServiceProxy.java:145)
at com.android.emailcommon.service.ServiceProxy.test(ServiceProxy.java:191)
at com.android.exchange.ExchangeService$7.run(ExchangeService.java:1850)
at com.android.emailcommon.utility.Utility$2.doInBackground(Utility.java:551)
at com.android.emailcommon.utility.Utility$2.doInBackground(Utility.java:549)
at android.os.AsyncTask$2.call(AsyncTask.java:287)
at java.util.concurrent.FutureTask.run(FutureTask.java:234)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
at java.lang.Thread.run(Thread.java:856)
08-04 12:38:35.068 322-474/system_process W/ActivityManager: Unbind failed: could not find connection for android.os.BinderProxy@411d82a8
08-04 12:38:35.118 708-711/com.android.exchange D/dalvikvm: GC_CONCURRENT freed 464K, 20% free 2503K/3112K, paused 80ms+7ms, total 189ms
08-04 12:38:42.870 322-337/system_process W/ActivityManager: Activity destroy timeout for ActivityRecord{411a3cd0 u0 com.example/.MainActivity}