Android - Handler 的简单应用

简单来说，Handler就是子进程用来向主线程传递消息的。

Handler可以当成子线程与主线程的消息传送的纽带。在安卓开发中，在子线程中无法刷新UI，是因为UI在子线程中刷新的话，是不安全的，就比如多个线程刷新UI，会造成UI更新冲突，这样是不安全的。

所以，Handler的作用就来了，子线程可以通过Handler来将UI更新操作切换到主线程中执行。

结合之前发的socket客户端例子来简单理解下：

目的：手机端按下温度，显示温度

客户端：MainActivity.java

package com.example.socketapp;

import java.io.IOException;
import java.io.OutputStream;
import java.net.Socket;
import java.net.UnknownHostException;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {

    Handler handler ;
    private TextView tx;
    private click connect;
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        //获取温度控件的ID
        tx=(TextView)findViewById(R.id.Temp);
        
        
        handler = new Handler(){
        	public void handleMessage(android.os.Message msg) {
        		//显示温度
        		tx.setText(connect.reTurnMes);
        	};
        	
        	
        };
    }

    public void Click_cmd(View v)
    {
    	int id=v.getId();
    	switch(id){
    		case R.id.openButton:
    			new click("open").Click_Button();
    			break;
    		case R.id.offButton:
    			new click("off").Click_Button();
    			break;
    		case R.id.getTemp:
    			connect = new click("getTemp",handler);
    			connect.Click_Button();
    	}
    }
    
}

客户端：activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
 	android:orientation="vertical"
    tools:context=".MainActivity" >

    <Button 
        android:id="@+id/openButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="开"
        android:onClick="Click_cmd"
        
        />
    <Button 
        android:id="@+id/offButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="关"
        android:onClick="Click_cmd"
        />
     <Button 
        android:id="@+id/getTemp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="获取温度"
        android:onClick="Click_cmd"
        />
     <TextView 
        android:id="@+id/Temp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="20 degree"
        android:onClick="Click_cmd"
        />
 

</LinearLayout>

客户端：Click.java

	package com.example.socketapp;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.Socket;
import java.net.UnknownHostException;

import android.os.Handler;
import android.widget.Toast;

public class Click {

	public String cmd;
	public String reTurnMes;
	public Handler handler;
	
	public Click(String cmd)
	{
		this.cmd=cmd;
	}
	public click(String cmd,Handler hangler)
	{
		this.cmd=cmd;
		this.handler=hangler;
	}
	
	public void Click_Button(){
		new Thread(new Runnable() {
			
			@Override
			public void run() {
				// TODO Auto-generated method stub
				try {
					
					Socket client = new Socket("192.168.1.29", 8787);
					
					OutputStream out=client.getOutputStream();
					
					out.write(cmd.getBytes());
					System.out.println("-------发送完成---------");
					
					if(cmd.equals("getTemp")){
						InputStream in = client.getInputStream();
						
						byte [] mes = new byte[128];
								
						int len;
						len = in.read(mes);
						
						System.out.println("----------读取"+new String(mes,0,len));
						
						reTurnMes = new String(mes,0,len);
						
						handler.sendEmptyMessage(0);
					}
					
				} catch (UnknownHostException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				} catch (IOException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
				
			}
		}).start();
	}

}

服务端：Server.java

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;


public class Server {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		int PORT= 8787;
		try {
			ServerSocket server = new ServerSocket(PORT);
			if(server!=null){
				System.out.println("创建服务端成功");
			}
			while(true){
				final Socket server_connect = server.accept();
				
				System.out.println("-----开始连接-----");
				
				new Thread(new Runnable() {
					
					public void run() {
						// TODO Auto-generated method stub
						try {
							InputStream in = server_connect.getInputStream();
							byte[] mes = new byte[128];
							
							int len ;
							len=in.read(mes);
							String message= new String(mes,0,len);
							
							System.out.println(message);
							System.out.println("数据接收完成");
							
							if(message.equals("getTemp")){
								
								OutputStream out = server_connect.getOutputStream();
								out.write("30 degree".getBytes());
								out.flush();
								out.close();
							}
							
							
							in.close();
							server_connect.close();
							
						} catch (IOException e) {
							// TODO Auto-generated catch block
							e.printStackTrace();
							System.out.println("服务器创建失败");
						}
					}
				}).start();
				
				
			}
			
			
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

}