Android经常使用UI组件

button（Button）是Android其中一个经常使用的UI组件。非常小可是在开发中最经常使用到。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button，这个button能够供用户点击。当用户对button进行操作的时候，触发对应事件，如点击。触摸。一般对于一个button而言，用的最多的就是点击事件，Button间接继承自View。而Android UI中的全部事件。都是定义在View中的。

实例：ButtonDemo
执行效果：


代码清单：
布局文件：main.xml

<?
xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
    <Button android:id="@+id/button1"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" android:text="Button1" />
    <Button android:id="@+id/button2"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" android:text="Button2" />
</LinearLayout>

Java源码文件：ActivityButton.java

package com.rainsong.buttondemo;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;

public class ActivityButton extends Activity
{
    Button btn1;
    Button btn2;
    
    OnClickListener listener1;
    OnClickListener listener2;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        listener1 = new OnClickListener() {
            public void onClick(View v) {
                Toast.makeText(ActivityButton.this, "Button1 clicked",Toast.LENGTH_SHORT).show();
            }
        };
        listener2 = new OnClickListener() {
            public void onClick(View v) {
                Toast.makeText(ActivityButton.this, "Button2 clicked",Toast.LENGTH_SHORT).show();
            }
        };

        btn1 = (Button)findViewById(R.id.button1);
        btn1.setOnClickListener(listener1);

        btn2 = (Button)findViewById(R.id.button2);
        btn2.setOnClickListener(listener2);
    }
}

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.