显示 TOAST 时尝试调用虚拟方法？ [复制]

Question

当您单击我的活动中的按钮时，它会启动/显示DatePickerDialog。当用户选择日期并单击“确定”时，我想在原始类（单击按钮的活动）中运行 AsyncTask。一切正常，但我想在 AsyncTask 完成时向用户显示一个 TOAST，但这样做时它不断收到错误。

这是我的代码：

BuyerHomePage.java 中的按钮方法

    public void MeetingCreator(){
        CalenderImageButton =     (ImageButton)findViewById(R.id.CalenderImageButton);
    CalenderImageButton.setOnClickListener(
            new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                                DialogFragment picker = new DatePickerFragment();
                                picker.show(getFragmentManager(), "datePicker");
           }
        }
    );
}

DatePickerFragment.java 代码

 public class DatePickerFragment extends DialogFragment
    implements DatePickerDialog.OnDateSetListener {

public static String formattedDate;

@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
// Use the current date as the default date in the picker
    final Calendar c = Calendar.getInstance();
    int year = c.get(Calendar.YEAR);
    int month = c.get(Calendar.MONTH);
    int day = c.get(Calendar.DAY_OF_MONTH);

// Create a new instance of DatePickerDialog and return it
    return new DatePickerDialog(getActivity(), this, year, month, day);
}

@Override
public void onDateSet(DatePicker view, int year, int month, int day) {
    Calendar c = Calendar.getInstance();
    c.set(year, month, day);

    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
    formattedDate = sdf.format(c.getTime());

    BuyerHomePage Meeting = new BuyerHomePage();
    Meeting.new MeetingSender().execute();
}
}

BuyerHomePage.java（AsyncTask 中的 post 方法）

@Override
    protected void onPostExecute (String result){

        if (result.equals("email sent")) {
            //This is where i get the error
            Toast.makeText(BuyerHomePage.this, "Email sent!", Toast.LENGTH_LONG).show();
        } else {
            Toast.makeText(BuyerHomePage.this, "Can't send email", Toast.LENGTH_LONG).show();
        }
    }

错误日志：

04-23 02:25:31.631 22071-22071/com.wilsapp.wilsapp E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.wilsapp.wilsapp, PID: 22071
    java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
    at android.content.ContextWrapper.getResources(ContextWrapper.java:87)
    at android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:81)
    at android.widget.Toast.<init>(Toast.java:102)
    at android.widget.Toast.makeText(Toast.java:259)
    at com.wilsapp.wilsapp.BuyerHomePage$MeetingSender.onPostExecute(BuyerHomePage.java:930)
    at com.wilsapp.wilsapp.BuyerHomePage$MeetingSender.onPostExecute(BuyerHomePage.java:836)
    at android.os.AsyncTask.finish(AsyncTask.java:651)
    at android.os.AsyncTask.-wrap1(AsyncTask.java)
    at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:668)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:148)
    at android.app.ActivityThread.main(ActivityThread.java:5417)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

如果有任何困惑或我需要解释任何事情，请发表评论！谢谢！

Answer 1

试试这个。

Toast.makeText(getApplicationContext(), "Email sent!", Toast.LENGTH_LONG).show();