6-2.Android 对话框之基础对话框问题清单（UI 线程问题、外部取消、冲突问题、dismiss 方法与 hide 方法）

对话框

1. 对话框（Dialog）是一种常用的 UI 组件，它主要用于显示信息、接收用户操作反馈

2. 对话框可以包含各种元素，但是主要还是以文本、按钮为主，其次是列表

3. 其中，基础对话框是 Android 中最简单的对话框，而后是进度对话框、自定义对话框等

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一、UI 线程问题

1、非 UI 线程中创建对话框

• 非 UI 线程中创建对话框会抛出异常

try {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();
} catch (Exception e) {e.printStackTrace();
}

• 输出结果

java.lang.RuntimeException: Can't create handler inside thread Thread[Thread-2,5,main] that has not called Looper.prepare()

2、非 UI 线程中显示对话框

• 非 UI 线程中显示对话框会抛出异常

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();new Thread(() -> {try {alertDialog.show();} catch (Exception e) {e.printStackTrace();}
}).start();

• 输出结果

java.lang.RuntimeException: Can't create handler inside thread Thread[Thread-2,5,main] that has not called Looper.prepare()

3、非 UI 线程中关闭对话框

• 非 UI 线程中关闭对话框不会抛出异常

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();new Thread(() -> {try {Thread.sleep(5 * 1000);alertDialog.dismiss();} catch (Exception e) {e.printStackTrace();}
}).start();

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二、外部取消

1、普通对话框外部取消

• 通过 setCancelable(boolean cancelable) 方法设置普通对话框是否可以通过点击外部区域来取消

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.setCancelable(false); // 不建议使用AlertDialog alertDialog = builder.create();alertDialog.show();

2、单选对话框外部取消

1. 通过 setCancelable(boolean cancelable) 方法设置单选对话框是否可以通过点击外部区域来取消

2. 但是不建议对单选对话框禁止点击外部区域来取消，因为用户可能误触发了单选对话框，本来不想做选择

AlertDialog.Builder builder = new AlertDialog.Builder(this);builder.setTitle("单选对话框");String[] items = {"物理", "化学", "生物", "历史"};
builder.setSingleChoiceItems(items, -1, (dialog, which) -> {Toast.makeText(this, "选择了：" + items[which], Toast.LENGTH_SHORT).show();dialog.dismiss();
});builder.setCancelable(false); // 不建议使用AlertDialog alertDialog = builder.create();alertDialog.show();

3、多选对话框外部取消

1. 通过 setCancelable(boolean cancelable) 方法设置多选对话框是否可以通过点击外部区域来取消

2. 但是不建议对多选对话框禁止点击外部区域来取消，因为用户可能误触发了多选对话框，本来不想做选择

AlertDialog.Builder builder = new AlertDialog.Builder(this);builder.setTitle("多选对话框");String[] items = {"胡萝卜", "白菜", "菠菜", "土豆", "黄瓜", "西红柿"};
boolean[] check = {false, false, false, false, false, false};
builder.setMultiChoiceItems(items, check, (dialog, which, isChecked) -> {if (isChecked) {check[which] = true;Toast.makeText(this, "你选中了：" + items[which], Toast.LENGTH_SHORT).show();} else {check[which] = false;Toast.makeText(this, "你取消了：" + items[which], Toast.LENGTH_SHORT).show();}
});builder.setCancelable(false); // 不建议使用AlertDialog alertDialog = builder.create();alertDialog.show();

4、列表对话框外部取消

1. 通过 setCancelable(boolean cancelable) 方法设置列表对话框是否可以通过点击外部区域来取消

2. 但是不建议对列表对话框禁止点击外部区域来取消，因为用户可能误触发了列表对话框，本来不想做选择

AlertDialog.Builder builder = new AlertDialog.Builder(this);builder.setTitle("课程安排：");String[] items = {"第一节（数学）", "第二节（地理）", "第三节（历史）", "第四节（美术）"};
builder.setItems(items, (dialog, which) -> {Toast.makeText(this, items[which], Toast.LENGTH_SHORT).show();
});builder.setCancelable(false);AlertDialog alertDialog = builder.create();alertDialog.show();

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三、冲突问题

1、单选对话框冲突问题

• setSingleChoiceItems 方法与 setMessage 方法显示区域互相冲突，同时使用时，setMessage 方法设置的内容会覆盖掉 setSingleChoiceItems 方法设置的内容

AlertDialog.Builder builder = new AlertDialog.Builder(this);builder.setTitle("单选对话框");
builder.setMessage("这是单选对话框");
String[] items = {"物理", "化学", "生物", "历史"};
builder.setSingleChoiceItems(items, -1, (dialog, which) -> {Toast.makeText(this, "选择了：" + items[which], Toast.LENGTH_SHORT).show();dialog.dismiss();
});AlertDialog alertDialog = builder.create();alertDialog.show();

2、多选对话框冲突问题

• setMultiChoiceItems 方法与 setMessage 方法显示区域互相冲突，同时使用时，setMessage 方法设置的内容会覆盖掉 setMultiChoiceItems 方法设置的内容

AlertDialog.Builder builder = new AlertDialog.Builder(this);builder.setTitle("多选对话框");
builder.setMessage("这是多选对话框");
String[] items = {"胡萝卜", "白菜", "菠菜", "土豆", "黄瓜", "西红柿"};
boolean[] check = {false, false, false, false, false, false};
builder.setMultiChoiceItems(items, check, (dialog, which, isChecked) -> {if (isChecked) {check[which] = true;Toast.makeText(this, "你选中了：" + items[which], Toast.LENGTH_SHORT).show();} else {check[which] = false;Toast.makeText(this, "你取消了：" + items[which], Toast.LENGTH_SHORT).show();}
});AlertDialog alertDialog = builder.create();alertDialog.show();

3、列表对话框冲突问题

• setItems 方法与 setMessage 方法显示区域互相冲突，同时使用时，setMessage 方法设置的内容会覆盖掉 setItems 方法设置的内容

AlertDialog.Builder builder = new AlertDialog.Builder(this);builder.setTitle("课程安排：");
builder.setMessage("这是列表对话框");
String[] items = {"第一节（数学）", "第二节（地理）", "第三节（历史）", "第四节（美术）"};
builder.setItems(items, (dialog, which) -> {Toast.makeText(this, items[which], Toast.LENGTH_SHORT).show();
});builder.setCancelable(false);AlertDialog alertDialog = builder.create();alertDialog.show();

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四、dismiss 方法与 hide 方法

1、基本介绍

1. dismiss 方法：用于完全关闭并移除 AlertDialog，一旦调用此方法，AlertDialog 将不再显示在屏幕上，且相关的资源会被移除

2. hide 方法：用于关闭 AlertDialog，一旦调用此方法，AlertDialog 将不再显示在屏幕上，但相关的资源不会被移除

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();
});AlertDialog alertDialog = builder.create();alertDialog.show();Handler handler = new Handler();handler.postDelayed(() -> alertDialog.hide(), 5 * 1000);