Android 对话框 - 基础对话框补充（不同的上下文创建 AlertDialog、AlertDialog 的三个按钮）

一、不同的上下文创建 AlertDialog

1、演示

（1）使用 Activity 上下文

AlertDialog.Builder builder = new AlertDialog.Builder(this);

builder.setTitle("普通对话框");
builder.setMessage("确定退出吗？");
builder.setPositiveButton("确定", (dialog, which) -> {
    Toast.makeText(this, "点击了确定", Toast.LENGTH_SHORT).show();
});
builder.setNegativeButton("取消", (dialog, which) -> {
    Toast.makeText(this, "点击了取消", Toast.LENGTH_SHORT).show();
});

AlertDialog alertDialog = builder.create();

alertDialog.show();

（2）使用 Application 上下文

1. 使用 getApplication 方法获取的 Application 上下文

AlertDialog.Builder builder = new AlertDialog.Builder(getApplication());

builder.setTitle("普通对话框");
builder.setMessage("确定退出吗？");
builder.setPositiveButton("确定", (dialog, which) -> {
    Toast.makeText(this, "点击了确定", Toast.LENGTH_SHORT).show();
});
builder.setNegativeButton("取消", (dialog, which) -> {
    Toast.makeText(this, "点击了取消", Toast.LENGTH_SHORT).show();
});

AlertDialog alertDialog = builder.create();

alertDialog.show();

• 输出结果

  android.view.WindowManager$BadTokenException: Unable to add window -- token null is not valid; is your activity running?

2. 使用 getApplicationContext 方法获取的 Application 上下文

AlertDialog.Builder builder = new AlertDialog.Builder(getApplicationContext());

builder.setTitle("普通对话框");
builder.setMessage("确定退出吗？");
builder.setPositiveButton("确定", (dialog, which) -> {
    Toast.makeText(this, "点击了确定", Toast.LENGTH_SHORT).show();
});
builder.setNegativeButton("取消", (dialog, which) -> {
    Toast.makeText(this, "点击了取消", Toast.LENGTH_SHORT).show();
});

AlertDialog alertDialog = builder.create();

alertDialog.show();

• 输出结果

  android.view.WindowManager$BadTokenException: Unable to add window -- token null is not valid; is your activity running?

2、小结

1. 应该总是使用 Activity 上下文来创建对话框

2. 避免使用 Application 上下文来创建对话框，对话框需要依附于一个窗口，而 Application 上下文没有关联的窗口

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二、AlertDialog 的三个按钮

1、基本介绍

按钮	说明
Positive Button	积极 / 确定按钮，通常表示确认或继续操作
Negative Button	消极 / 取消按钮，通常表示取消操作
Neutral Button	中性按钮，提供第三种选择

2、演示

AlertDialog.Builder builder = new AlertDialog.Builder(this);

builder.setTitle("普通对话框");
builder.setMessage("确定退出吗？");
builder.setPositiveButton("确定", (dialog, which) -> {
    Toast.makeText(this, "点击了确定", Toast.LENGTH_SHORT).show();
});
builder.setNegativeButton("取消", (dialog, which) -> {
    Toast.makeText(this, "点击了取消", Toast.LENGTH_SHORT).show();
});
builder.setNeutralButton("稍后", (dialog, which) -> {
    Toast.makeText(this, "点击了稍后", Toast.LENGTH_SHORT).show();
});

AlertDialog alertDialog = builder.create();

alertDialog.show();