Android常用UI组件 - Button

按钮（Button）是Android当中一个常用的UI组件，很小但是在开发中最常用到。一般通过与监听器结合使用，从而触发一些特定事件。 Button继承了TextView。它的功能就是提供一个按钮，这个按钮可以供用户点击，当用户对按钮进行操作的时候，触发相应事件，如点击，触摸。一 般对于一个按钮而言，用的最多的就是点击事件，Button间接继承自View，而Android UI中的所有事件，都是定义在View中的。

实例：ButtonDemo
运行效果：


代码清单：
布局文件：main.xml

[html] view plaincopy

1. <?xml version="1.0" encoding="utf-8"?>  
2. <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"  
3.     android:orientation="vertical"  
4.     android:layout_width="fill_parent"  
5.     android:layout_height="fill_parent"  
6.     >  
7.     <Button android:id="@+id/button1"  
8.         android:layout_width="fill_parent"  
9.         android:layout_height="wrap_content" android:text="Button1" />  
10.     <Button android:id="@+id/button2"  
11.         android:layout_width="fill_parent"  
12.         android:layout_height="wrap_content" android:text="Button2" />  
13. </LinearLayout>  

Java源代码文件：ActivityButton.java

[java] view plaincopy

1. package com.rainsong.buttondemo;  
2.   
3. import android.app.Activity;  
4. import android.os.Bundle;  
5. import android.view.View;  
6. import android.view.View.OnClickListener;  
7. import android.widget.Button;  
8. import android.widget.Toast;  
9.   
10. public class ActivityButton extends Activity  
11. {  
12.     Button btn1;  
13.     Button btn2;  
14.       
15.     OnClickListener listener1;  
16.     OnClickListener listener2;  
17.   
18.     /** Called when the activity is first created. */  
19.     @Override  
20.     public void onCreate(Bundle savedInstanceState)  
21.     {  
22.         super.onCreate(savedInstanceState);  
23.         setContentView(R.layout.main);  
24.   
25.         listener1 = new OnClickListener() {  
26.             public void onClick(View v) {  
27.                 Toast.makeText(ActivityButton.this, "Button1 clicked",Toast.LENGTH_SHORT).show();  
28.             }  
29.         };  
30.         listener2 = new OnClickListener() {  
31.             public void onClick(View v) {  
32.                 Toast.makeText(ActivityButton.this, "Button2 clicked",Toast.LENGTH_SHORT).show();  
33.             }  
34.         };  
35.   
36.         btn1 = (Button)findViewById(R.id.button1);  
37.         btn1.setOnClickListener(listener1);  
38.   
39.         btn2 = (Button)findViewById(R.id.button2);  
40.         btn2.setOnClickListener(listener2);  
41.     }  
42. }  

API知识点
Activity
public class
Activity
extends ContextThemeWrapper
implements ComponentCallbacks2 KeyEvent.Callback LayoutInflater.Factory2 View.OnCreateContextMenuListener Window.Callback

View     findViewById(int id)
Finds a view that was identified by the id attribute from the XML that was processed in onCreate(Bundle).

void     setContentView(int layoutResID)
Set the activity content from a layout resource.

View
public class
View
extends Object
implements Drawable.Callback KeyEvent.Callback AccessibilityEventSource

void     setOnClickListener(View.OnClickListener l)
Register a callback to be invoked when this view is clicked.

Button
public class
Button
extends TextView

View.OnClickListener
public static interface
View.OnClickListener

abstract void    onClick(View v)
Called when a view has been clicked.

Toast
public class
Toast
extends Object

Constants
int        LENGTH_LONG        Showthe view or text notification for a long period of time.
int        LENGTH_SHORT        Showthe view or text notification for a short period of time.

static Toast
makeText(Context context, int resId, int duration)
Make a standard toast that just contains a text view with the text from a resource.

static Toast
makeText(Context context, CharSequence text, int duration)
Make a standard toast that just contains a text view.
 
void
show()
Show the view for the specified duration.