我无法完成代码。一切都有效，除了一件事。我一直得到一个null错误，它引用了无法调用的webViewClient。该应用程序工作正常，除非我关闭WiFi和移动网络。它应该显示一个对话框，但应用程序停止。我已经有了它的工作，但显然我已经改变了一些坏事。这是我的错误：
07-12 12:59:33.770 21023-21023/companyname.appname
E/AndroidRuntime: FATAL EXCEPTION: main
Process: companyname.appname, PID: 21023
java.lang.RuntimeException: Unable to start activity ComponentInfo{companyname.appname/companyname.appname.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.webkit.WebView.setWebViewClient(android.webkit.WebViewClient)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.webkit.WebView.setWebViewClient(android.webkit.WebViewClient)' on a null object reference
at companyname.appname.MainActivity.onCreate(MainActivity.java:49)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
这是我的代码的一部分：
public class MainActivity extends AppCompatActivity {
WebView browser;
FloatingActionButton fab_plus,fab_settings,fab_share, fab_report;
Animation FabOpen,FabClose,FabRClockwise,FabRantiClockwise;
boolean isOpen = false;
boolean doubleBackToExitPressedOnce = false;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if(!isConnected(MainActivity.this)) buildDialog(MainActivity.this).show();
else {
setContentView(R.layout.activity_main);
}
browser=(WebView) findViewById(R.id.webView);
browser.setWebViewClient(new WebViewClient() {
@Override
public boolean shouldOverrideUrlLoading(WebView view, String url) {
view.loadUrl(url);
return (true);
}
});
String url = "here's my url";
WebView view = (WebView) this.findViewById(R.id.webView);
view.getSettings().setJavaScriptEnabled(true);
CookieManager.getInstance().setAcceptCookie(true);
view.loadUrl(url);
//Over here there's a lot of code which I think is irrelevant for this problem. And then at the bottom there's my dialog and internet check:
public boolean isConnected(Context context) {
ConnectivityManager cm = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo netinfo = cm.getActiveNetworkInfo();
if (netinfo != null && netinfo.isConnectedOrConnecting()) {
NetworkInfo wifi = cm.getNetworkInfo(ConnectivityManager.TYPE_WIFI);
NetworkInfo mobile = cm.getNetworkInfo(ConnectivityManager.TYPE_MOBILE);
if((mobile != null && mobile.isConnectedOrConnecting()) || (wifi != null && wifi.isConnectedOrConnecting())) return true;
else return false;
} else
return false;
}
public AlertDialog.Builder buildDialog(Context c) {
AlertDialog.Builder builder = new AlertDialog.Builder(c);
builder.setTitle("No connection");
builder.setMessage("Text");
builder.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
finish();
}
});
return builder;
}
}
此处是activity_main XMl文件中Webview的一部分：
<WebView
android:id="@+id/webView"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_alignParentBottom="true"
android:layout_alignParentEnd="true"
android:layout_alignParentLeft="true"
android:layout_alignParentRight="true"
android:layout_alignParentStart="true"
android:layout_alignParentTop="true">
</WebView>
我觉得这很简单，我无法看到。你们有什么想法吗？非常感谢提前！
答案 0 :(得分：0)
摆脱这条线：
browser.setWebViewClient(new WebViewClient());
首先，在为browser分配值之前，您正在调用它。这会导致你的崩溃。
其次，你以后第二次打电话给setWebViewClient()，这使得这条线毫无意义。
答案 1 :(得分：0)
而不是
browser.setWebViewClient(new WebViewClient());
browser=(WebView) findViewById(R.id.webView);
写这个
browser=(WebView) findViewById(R.id.webView); //first get reference
browser.setWebViewClient(new WebViewClient()); //then call method
答案 2 :(得分：0)
问题是您在实例化webview之前调用此方法
browser.setWebViewClient(new WebViewClient()); <-- remove this line
//Zorgt ervoor dat de browser de app niet verlaat
browser=(WebView) findViewById(R.id.webView);
browser.setWebViewClient(new WebViewClient()
应该做的伎俩