Android中的对话框之二：AlertDialog扩展

有的时候，可能需要弹出一个对话框，以便从用户的输入来获取某些确认信息。这种情况下，可以重写Activity基类中的受保护方法（protected）onCreateDialog()。

1、创建一个工程：Dialog。

2、main.xml中的代码。

[java] view
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<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="fill_parent"

android:layout_height="fill_parent"

android:orientation="vertical" >

<Button

android:id="@+id/btn_dialog"

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:text="Click to display a dialog"

android:onClick="onClick" />

</LinearLayout>

3、DialogActivity.java中的代码。

[java] view
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package net.horsttnann.Dialog;

import android.app.Activity;

import android.app.AlertDialog;

import android.app.Dialog;

import android.content.DialogInterface;

import android.os.Bundle;

import android.view.View;

import android.widget.Toast;

public class DialogActivity extends Activity {

CharSequence[] items = { "Google", "Apple", "Microsoft" };

boolean[] itemsChecked = new boolean[items.length];

/** Called when the activity is first created. */

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

}

public void onClick(View v) {

showDialog(0);

}

@Override

protected Dialog onCreateDialog(int id) {

switch (id) {

case 0:

return new AlertDialog.Builder(this)

.setIcon(R.drawable.ic_launcher)

.setTitle("This is a dialog with some simple text...")

.setPositiveButton("OK",

new DialogInterface.OnClickListener() {

public void onClick(DialogInterface dialog,

int whichButton) {

Toast.makeText(getBaseContext(),

"OK clicked!", Toast.LENGTH_SHORT)

.show();

}

})

.setNegativeButton("Cancel",

new DialogInterface.OnClickListener() {

public void onClick(DialogInterface dialog,

int whichButton) {

Toast.makeText(getBaseContext(),

"Cancel clicked!",

Toast.LENGTH_SHORT).show();

}

})

.setMultiChoiceItems(items, itemsChecked,

new DialogInterface.OnMultiChoiceClickListener() {

public void onClick(DialogInterface dialog,

int which, boolean isChecked) {

Toast.makeText(

getBaseContext(),

items[which]

+ (isChecked ? " checked!"

: " unchecked!"),

Toast.LENGTH_SHORT).show();

}

}).create();

}

return null;

}

}

4、调试。

点击按钮弹出对话框，在CheckBox上面打勾，就会弹出一个Toast提示，显示选中物件的文本信息。点击“OK”或“Cancel”按钮会使对话框消失。



想要显示对话框，首先要重写Activity基类中的onCreateDialog()方法：

[java] view
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@Override

protected Dialog onCreateDialog(int id) {

// ...

}

当调用showDialog()的时候，上面被重写的方法就被调用了：

[java] view
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public void onClick(View v) {

showDialog(0);

}

这个创建对话框的onCreateDialog()方法是一个被Activity控制的回调函数，当调用showDialog()时，onCreateDialog()回调函数就被触发了。showDialog()方法接受一个Integer参数，用来识别到底要显示哪个对话框。一般情况下，使用switch语句去判断显示不同的对话框。

想要创建一个对话框，还需要使用AlertDialog类的Builder构造器，设置不同的属性，比如图标、标题、按钮、单选框等等：

[java] view
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@Override

protected Dialog onCreateDialog(int id) {

switch (id) {

case 0:

Builder builder = new AlertDialog.Builder(this);

builder.setIcon(R.drawable.ic_launcher);

builder.setTitle("This is a dialog with some simple text...");

builder.setPositiveButton("OK",

new DialogInterface.OnClickListener() {

public void onClick(DialogInterface dialog,

int whichButton) {

Toast.makeText(getBaseContext(), "OK clicked!",

Toast.LENGTH_SHORT).show();

}

});

builder.setNegativeButton("Cancel",

new DialogInterface.OnClickListener() {

public void onClick(DialogInterface dialog,

int whichButton) {

Toast.makeText(getBaseContext(), "Cancel clicked!",

Toast.LENGTH_SHORT).show();

}

});

builder.setMultiChoiceItems(items, itemsChecked,

new DialogInterface.OnMultiChoiceClickListener() {

public void onClick(DialogInterface dialog, int which,

boolean isChecked) {

Toast.makeText(

getBaseContext(),

items[which]

+ (isChecked ? " checked!"

: " unchecked!"),

Toast.LENGTH_SHORT).show();

}

});

return builder.create();

}

return null;

}