调用 DatePickerDialog Show 时无法添加 Window 异常

Question

我是 Android Studio 和 Android 开发的新手，但通过一些在线查询，我必须编写一个 class 来处理 DatePickerDialog 和 TimePickerDialog 请求以设置日期.

基于我写的例子 class:

class DatePick
{
    protected android.app.Activity activity;
    public final java.util.Calendar currentDate = java.util.Calendar.getInstance();
    private boolean picked;
    public java.util.Calendar date;

    public java.util.Calendar pickDate()
    {
        this.picked = false;
        this.date = java.util.Calendar.getInstance();
        android.app.DatePickerDialog datePicker = new android.app.DatePickerDialog(this.activity.getApplicationContext(), new android.app.DatePickerDialog.OnDateSetListener() { @Override public void onDateSet(android.widget.DatePicker view, int year, int month, int dayOfMonth) { cweb.companion.DatePick.this.date.set(view.getYear(), view.getMonth(), view.getDayOfMonth()); } }, this.currentDate.get(java.util.Calendar.YEAR), this.currentDate.get(java.util.Calendar.MONTH), this.currentDate.get(java.util.Calendar.DAY_OF_MONTH)) { @Override public void onClick(android.content.DialogInterface dialog, int which) { cweb.companion.DatePick.this.picked = (which == android.content.DialogInterface.BUTTON_POSITIVE); } };
        datePicker.show(); //todo resolve: exception here for unable to add window null token
        datePicker = null; //dispose?
        if (this.picked)
        {
            android.app.TimePickerDialog timePicker = new android.app.TimePickerDialog(this.activity.getApplicationContext(), new android.app.TimePickerDialog.OnTimeSetListener() { @Override public void onTimeSet(android.widget.TimePicker view, int hourOfDay, int minute) { cweb.companion.DatePick.this.date.set(cweb.companion.DatePick.this.date.get(java.util.Calendar.YEAR), cweb.companion.DatePick.this.date.get(java.util.Calendar.MONTH), cweb.companion.DatePick.this.date.get(java.util.Calendar.DAY_OF_MONTH), hourOfDay, minute); } }, this.currentDate.get(java.util.Calendar.HOUR_OF_DAY), this.currentDate.get(java.util.Calendar.MINUTE), true) { @Override public void onClick(android.content.DialogInterface dialog, int which) { cweb.companion.DatePick.this.picked = (which == android.content.DialogInterface.BUTTON_POSITIVE); } };
            timePicker.show(); //picked may change back to false after that (maybe, depending on the user's confirm/abort)
            timePicker = null; //dispose?
        }
        if (!this.picked) { this.date = null; }
        return cweb.companion.DatePick.this.date;
    }

    public static java.lang.String toString(java.util.Calendar date) { return java.lang.String.format("%02d", date.get(java.util.Calendar.DAY_OF_MONTH)) + "/" + java.lang.String.format("%02d", date.get(java.util.Calendar.MONTH)) + "/" + java.lang.String.format("%04d", date.get(java.util.Calendar.YEAR)) + " " + java.lang.String.format("%02d", date.get(java.util.Calendar.HOUR_OF_DAY)) + ":" + java.lang.String.format("%02d", date.get(java.util.Calendar.MINUTE)) + ":" + java.lang.String.format("%02d", date.get(java.util.Calendar.SECOND)); }
    public DatePick(android.app.Activity activity) { this.activity = activity; }
}

然后通过以下声明在我的 MainActivity（应用程序中唯一的 activity）中调用它：

public class MainActivity extends androidx.appcompat.app.AppCompatActivity
{
    protected android.widget.Button datePickCall;
    private java.util.Calendar date;

    private void pickdatePickCall()
    {
        cweb.companion.DatePick picker = new cweb.companion.DatePick(this);
        this.date = picker.pickDate();
        this.datePickCall.setText(cweb.companion.DatePick.toString(this.date));
    }

    @Override protected void onCreate(android.os.Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        this.setContentView(cweb.companion.R.layout.activity_main);
        this.datePickCall = this.findViewById(cweb.companion.R.id.datePickCall);
        this.datePickCall.setOnClickListener(new android.view.View.OnClickListener() { @Override public void onClick(android.view.View v) { cweb.companion.MainActivity.this.pickdatePickCall(); }});
    }
}

但是当我调试应用程序时，在 DatePick class 处标有待办事项的行上，它调用了对话框的 "show()" 方法，我得到一个异常：

Unable to add window - Token null, is activity running?

似乎无法理解它为什么不起作用，有什么帮助吗？

Answer 1

尝试用 activity 上下文替换应用程序上下文。

DatePickerDialog(Context context) Creates a new date picker dialog for the current date using the parent context's default date picker dialog theme.

来源： https://developer.android.com/reference/android/app/DatePickerDialog

更新：我知道这看起来很矛盾。可以假设应用程序上下文拥有 activity 拥有的一切，甚至更多。但事实并非如此。 getApplicationContext() 不能用于启动对话框。 More here.

对于您的代码：当您编写 new cweb.companion.DatePick(this); 时，您已经传递了 activity 上下文，因此您可以去掉 getApplicationContext() 并编写 new DatePickerDialog(activity, new ...

我还注意到您总是在不必要的时候使用 this.。例如我会更换 this.picked = false; 与 picked = false;

并且您可以使用导入来摆脱那些长包名称。我会替换

之类的东西

android.app.DatePickerDialog datePicker = new android.app.DatePickerDialog(...

和

import android.app.DatePickerDialog;
public class DatePick { ...
DatePickerDialog datePicker = new DatePickerDialog(...

只是为了更容易阅读代码。尝试一下，希望对您有所帮助。

更新二： 以下代码在我的电脑上运行。它显示了对话框，然后是祝酒词。尝试使其适应您的需要。如果这对您不起作用，那么我不知道原因。 ;)

package com.something.dialogtest;

import android.app.DatePickerDialog;
import android.os.Bundle;
import android.widget.DatePicker;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;

import java.util.Calendar;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        DatePickerDialog datePicker = new DatePickerDialog(this,
                new DatePickerDialog.OnDateSetListener() {
                    @Override
                    public void onDateSet(DatePicker view, int year, int month, int dayOfMonth) {
                        Toast.makeText(MainActivity.this, "onDateSet", Toast.LENGTH_SHORT).show();
                    }
                },
                Calendar.getInstance().get(Calendar.YEAR),
                Calendar.getInstance().get(Calendar.MONTH),
                Calendar.getInstance().get(Calendar.DAY_OF_MONTH));
        datePicker.show();
    }
}

调用 DatePickerDialog Show 时无法添加 Window 异常

Unable to Add Window Exception on calling DatePickerDialog Show

java

android

android-alertdialog

android-studio