我正在开发一个简单的网络应用。几天前，它与后退按钮一起工作得很好。但我最近添加了admob，除了模拟器和设备中的后退按钮外，一切正常。它说出乎意料地停了下来。
我用Google搜索并搜索了stackoverflow，找到了一个同名的问题，但答案不正确。所以这不是一个重复的问题。
这是mainActivity.java
public class MainActivity extends Activity {
private WebView WebView;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
getWindow().requestFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.main);
WebView WebView = (WebView) findViewById(R.id.webView);
WebView.loadUrl("file:///android_asset/index.html");
WebView.getSettings().setJavaScriptEnabled(true);
WebView.setWebViewClient(new WebViewClient() {
@Override
public boolean shouldOverrideUrlLoading(WebView view, String url) {
view.loadUrl(url);
return true;
}
});
}
// For Options Menu
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.main, menu);
return true;
}
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.about:
startActivity(new Intent(this, About.class));
return true;
case R.id.exit:
finish();
return true;
default:
return super.onOptionsItemSelected(item);
}
}
@Override
public boolean onKeyDown(final int keyCode, final KeyEvent event) {
if ((keyCode == KeyEvent.KEYCODE_BACK) && WebView.canGoBack()) {
WebView.goBack();
return true;
}
return super.onKeyDown(keyCode, event);
}
}
首先，我无法在我的WebView中放置广告，因此此XML代码与之前的版本不同（当后退密钥正常工作时）。我有从不同来源粘贴的副本来修复它，但现在广告和WebView完全正常工作，除了后退键。
这是main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:ads="http://schemas.android.com/apk/lib/com.google.ads"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<WebView
android:id="@+id/webView"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1.02" />
<com.google.ads.AdView
android:id="@+id/adView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
ads:adSize="BANNER"
ads:adUnitId="my ad id"
ads:loadAdOnCreate="true" >
</com.google.ads.AdView>
</LinearLayout>
从logcat
登录06-27 23:10:40.000: V/WebRequest(10155): WebRequest::WebRequest, setPriority = 1
06-27 23:10:40.030: V/chromium(10155): external/chromium/net/disk_cache/hostres_plugin_bridge.cc:52: [0627/231040:INFO:hostres_plugin_bridge.cc(52)] StatHubCreateHostResPlugin initializing...
06-27 23:10:40.030: V/chromium(10155): external/chromium/net/disk_cache/hostres_plugin_bridge.cc:57: [0627/231040:INFO:hostres_plugin_bridge.cc(57)] StatHubCreateHostResPlugin lib loaded
06-27 23:10:40.040: V/chromium(10155): external/chromium/net/disk_cache/hostres_plugin_bridge.cc:63: [0627/231040:INFO:hostres_plugin_bridge.cc(63)] StatHubCreateHostResPlugin plugin connected
06-27 23:10:40.040: V/chromium(10155): external/chromium/net/http/http_cache.cc:1167: [0627/231040:INFO:http_cache.cc(1167)] HttpCache::OnBackendCreated HostStat created
06-27 23:10:40.040: E/chromium(10155): external/chromium/net/disk_cache/stat_hub.cc:213: [0627/231040:ERROR:stat_hub.cc(213)] StatHub::Init - App com.example.mywebapp isn't supported.
06-27 23:10:40.050: E/chromium(10155): external/chromium/net/disk_cache/stat_hub.cc:213: [0627/231040:ERROR:stat_hub.cc(213)] StatHub::Init - App com.example.mywebapp isn't supported.
06-27 23:10:40.050: W/chromium(10155): external/chromium/net/disk_cache/backend_impl.cc:1829: [0627/231040:WARNING:backend_impl.cc(1829)] Destroying invalid entry.
06-27 23:10:41.590: I/QC_RIL_OEM_HOOK(10155): QcRilOemHook Service Created Successfully
06-27 23:10:41.590: V/QC_RIL_OEM_HOOK(10155): sendQcRilOemHookMsg: Outgoing Data is 5155414c434f4d4d0300080006000000726d6e657430
06-27 23:10:45.660: W/dalvikvm(10155): threadid=1: thread exiting with uncaught exception (group=0x40aa2390)
06-27 23:10:45.660: E/AndroidRuntime(10155): FATAL EXCEPTION: main
06-27 23:10:45.660: E/AndroidRuntime(10155): java.lang.NullPointerException
06-27 23:10:45.660: E/AndroidRuntime(10155): at com.example.mywebapp.MainActivity.onKeyDown(MainActivity.java:57)
06-27 23:10:45.660: E/AndroidRuntime(10155): at android.view.KeyEvent.dispatch(KeyEvent.java:2551)
06-27 23:10:45.660: E/AndroidRuntime(10155): at android.app.Activity.dispatchKeyEvent(Activity.java:2329)
06-27 23:10:45.660: E/AndroidRuntime(10155): at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:1806)
06-27 23:10:45.660: E/AndroidRuntime(10155): at android.view.ViewRootImpl.deliverKeyEventPostIme(ViewRootImpl.java:3342)
06-27 23:10:45.660: E/AndroidRuntime(10155): at android.view.ViewRootImpl.handleFinishedEvent(ViewRootImpl.java:3315)
06-27 23:10:45.660: E/AndroidRuntime(10155): at android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2460)
06-27 23:10:45.660: E/AndroidRuntime(10155): at android.os.Handler.dispatchMessage(Handler.java:99)
06-27 23:10:45.660: E/AndroidRuntime(10155): at android.os.Looper.loop(Looper.java:137)
06-27 23:10:45.660: E/AndroidRuntime(10155): at android.app.ActivityThread.main(ActivityThread.java:4456)
06-27 23:10:45.660: E/AndroidRuntime(10155): at java.lang.reflect.Method.invokeNative(Native Method)
06-27 23:10:45.660: E/AndroidRuntime(10155): at java.lang.reflect.Method.invoke(Method.java:511)
06-27 23:10:45.660: E/AndroidRuntime(10155): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:787)
06-27 23:10:45.660: E/AndroidRuntime(10155): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:554)
06-27 23:10:45.660: E/AndroidRuntime(10155): at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：2)
WebView为null，因为在onCreate函数中，您创建了一个名为WebView的局部变量，因此您的赋值不会分配给实例变量。变化
WebView WebView = (WebView) findViewById(R.id.webView);
到
WebView = (WebView) findViewById(R.id.webView);