当我尝试从片段内部的Web视图向后导航时,我一直收到错误,可能导致此问题的原因是什么?
我的logcat:
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: FATAL EXCEPTION: main
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: Process: pi.com.ndtc, PID: 28567
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.webkit.WebView.canGoBack()' on a null object reference
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at pi.com.ndtc.SocialActivity.onKeyDown(SocialActivity.java:343)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.KeyEvent.dispatch(KeyEvent.java:2619)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.app.Activity.dispatchKeyEvent(Activity.java:2707)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.support.v7.internal.view.WindowCallbackWrapper.dispatchKeyEvent(WindowCallbackWrapper.java:50)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.support.v7.app.AppCompatDelegateImplBase$AppCompatWindowCallbackBase.dispatchKeyEvent(AppCompatDelegateImplBase.java:224)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.support.v7.internal.view.WindowCallbackWrapper.dispatchKeyEvent(WindowCallbackWrapper.java:50)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:2276)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.ViewRootImpl$ViewPostImeInputStage.processKeyEvent(ViewRootImpl.java:4020)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:3982)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3544)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3597)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3563)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3680)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3571)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3737)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3544)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3597)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3563)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3571)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3544)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3597)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3563)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3713)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.ViewRootImpl$ImeInputStage.onFinishedInputEvent(ViewRootImpl.java:3874)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.inputmethod.InputMethodManager$PendingEvent.run(InputMethodManager.java:2208)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.inputmethod.InputMethodManager.invokeFinishedInputEventCallback(InputMethodManager.java:1849)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.inputmethod.InputMethodManager.finishedInputEvent(InputMethodManager.java:1840)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.inputmethod.InputMethodManager$ImeInputEventSender.onInputEventFinished(InputMethodManager.java:2185)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.view.InputEventSender.dispatchInputEventFinished(InputEventSender.java:141)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.os.MessageQueue.nativePollOnce(Native Method)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.os.MessageQueue.next(MessageQueue.java:143)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.os.Looper.loop(Looper.java:122)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5257)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:372)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
10-10 22:42:23.926 28567-28567/pi.com.ndtc E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
logcat指向此行
at pi.com.ndtc.SocialActivity.onKeyDown(SocialActivity.java:343)
这是:
if ((keyCode == KeyEvent.KEYCODE_BACK) && myWebViewInstagram.canGoBack())
这是我用来尝试在网络视图中向后导航的方法:
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
WebView myWebViewInstagram = (WebView) findViewById(R.id.webview_instagram);
// Check if the key event was the Back button and if there's history
if ((keyCode == KeyEvent.KEYCODE_BACK) && myWebViewInstagram.canGoBack()) {
myWebViewInstagram.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);
}
我的片段:
public class FragmentThree extends Fragment {
public FragmentThree(){
//Required empty constructor
}
@Override
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
}
@Override
public View onCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState){
// Inflate the layout for this fragment
//return inflater.inflate(R.layout.fragment_two, container, false);
//Using the "View" to obtain the WebView
View viewInsta = inflater.inflate(R.layout.fragment_three, container, false);
//in app WebView
WebView myInstagramWebView = (WebView) viewInsta.findViewById(R.id.webview_instagram);
WebSettings webSettings = myInstagramWebView.getSettings();//required for enabling javascript
webSettings.setJavaScriptEnabled(true); //javascript was disabled by default by webView; i enabled it
myInstagramWebView.setWebViewClient(new WebViewClient());
myInstagramWebView.setWebChromeClient(new WebChromeClient());
final ProgressDialog dialog;
dialog = new ProgressDialog(getActivity(),R.style.MyDialogTheme);
//dialog.setMessage("Loading...");
dialog.show();
myInstagramWebView.loadUrl("https://instagram.com/ndtcjamaica/");
myInstagramWebView.setWebViewClient(new WebViewClient() {
public void onPageFinished(WebView myInstagramWebView, String url) {
// DISMISS PROGRESS DIALOG HERE
dialog.dismiss();
}
}
);
return viewInsta;
}
}
答案 0 :(得分:2)
使用此mWebView
应该是您的网页浏览
你必须声明它
private WebView mWebView;
使用onCreate()
方法对其进行初始化,您应该很高兴。
mWebView = (WebView) findViewById(R.id.webView);
然后使用下面的代码进行活动
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (event.getAction() == KeyEvent.ACTION_DOWN) {
switch (keyCode) {
case KeyEvent.KEYCODE_BACK:
if (mWebView.canGoBack()) {
mWebView.goBack();
} else {
finish();
}
return true;
}
}
return super.onKeyDown(keyCode, event);
}
如果您在片段
中使用此功能webView.setOnKeyListener(new 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;
}
});
从所有片段调用使用波纹管方法
((YourActivityClassName)getActivity()).yourPublicMethod();