Question

我正在调用方法AlertUser.alertUser(getActivity());，它具有来自片段的alertDialog，但它会抛出NPE错误

 new Handler().postDelayed(new Runnable() {
                    @Override
                    public void run() {

                    if(flag==false)
                        {
                    progressDialog.cancel();
                    AlertUser.alertUser(getActivity());
                    cancel(true);
                        }
                    }
                }, 30000);

alertUser方法：

public static void alertUser(Context context)
    {
        AlertDialog.Builder alertDialog=new AlertDialog.Builder(context); 


        alertDialog.setTitle("Connection failure...!"+"\n");

        alertDialog.setMessage("\n"+"It looks like you have lost network connection. Please check your network connection or wait to re-connect"+"\n");





        // Setting  "Yes" Button
        alertDialog.setPositiveButton("Ok", new DialogInterface.OnClickListener() {

            @Override
            public void onClick(DialogInterface dialog,int which) {


                    /*Intent noNetwork=new Intent(android.provider.Settings.ACTION_WIRELESS_SETTINGS);
                    startActivityForResult(noNetwork,1443);*/



            }
        });

        alertDialog.show();
    }

logcat的

02-05 15:47:06.440: E/AndroidRuntime(12050): FATAL EXCEPTION: main
02-05 15:47:06.440: E/AndroidRuntime(12050): java.lang.NullPointerException
02-05 15:47:06.440: E/AndroidRuntime(12050):    at android.app.AlertDialog.resolveDialogTheme(AlertDialog.java:142)
02-05 15:47:06.440: E/AndroidRuntime(12050):    at android.app.AlertDialog$Builder.<init>(AlertDialog.java:359)
02-05 15:47:06.440: E/AndroidRuntime(12050):    at com.abs.deliveryboy.AlertUser.alertUser(AlertUser.java:11)
02-05 15:47:06.440: E/AndroidRuntime(12050):    at com.abs.deliveryboy.NewOrdersFragment$NewOrderTask$1.run(NewOrdersFragment.java:159)
02-05 15:47:06.440: E/AndroidRuntime(12050):    at android.os.Handler.handleCallback(Handler.java:615)
02-05 15:47:06.440: E/AndroidRuntime(12050):    at android.os.Handler.dispatchMessage(Handler.java:92)
02-05 15:47:06.440: E/AndroidRuntime(12050):    at android.os.Looper.loop(Looper.java:137)
02-05 15:47:06.440: E/AndroidRuntime(12050):    at android.app.ActivityThread.main(ActivityThread.java:4800)
02-05 15:47:06.440: E/AndroidRuntime(12050):    at java.lang.reflect.Method.invokeNative(Native Method)
02-05 15:47:06.440: E/AndroidRuntime(12050):    at java.lang.reflect.Method.invoke(Method.java:511)
02-05 15:47:06.440: E/AndroidRuntime(12050):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
02-05 15:47:06.440: E/AndroidRuntime(12050):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:556)
02-05 15:47:06.440: E/AndroidRuntime(12050):    at dalvik.system.NativeStart.main(Native Method)

Answer 1

您传递给AlertDialog.Builder构造函数的上下文是null，因此是NPE。

如果片段未附加到活动，片段getActivity()将返回null。由于您将异步runnable发布到处理程序，因此无法保证在runnable运行时将该片段附加到活动。

您应该将有效的活动上下文作为参数传递给您使用getActivity()查询它的runnable。请注意，保留活动引用是一种容易导致内存泄漏的方法。

Answer 2

正如@FD_所说，你无法从后台线程启动警告对话框。在后台线程中使用getActivity()时，它返回null，因此返回NPE。您正在将null对象传递给另一个方法。最好在同一个活动/线程上做。

Answer 3

试试这个..

public static void alertUser(Context context)
    {
        AlertDialog.Builder alertDialog=new AlertDialog.Builder(context); 


        alertDialog.setTitle("Connection failure...!"+"\n");

        alertDialog.setMessage("\n"+"It looks like you have lost network connection. Please check your network connection or wait to re-connect"+"\n");





        // Setting  "Yes" Button
        alertDialog.setPositiveButton("Ok", new DialogInterface.OnClickListener() {

            @Override
            public void onClick(DialogInterface dialog,int which) {


                    /*Intent noNetwork=new Intent(android.provider.Settings.ACTION_WIRELESS_SETTINGS);
                    startActivityForResult(noNetwork,1443);*/



            }
        });
//previously it was like this alertDialog.show(); but it should be like this
        alertDialog.create.show();
    }

创建alertdialog时的NPE

3 个答案: