Android学习笔记（四） 定时器Timer

Android考虑到线程安全问题，不允许在线程中执行UI线程。

所以在线程中不允许有UI操作

可以利用Handler机制来接收Timer每隔一秒发出的信息，也可以直接利用handler机制的

1、方法一:Handler+Thread

package com.example.yuyin_lixian;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;

import java.util.Timer;
import java.util.TimerTask;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

/**
 * handler定时器
 *
 * @author Smalt
 *
 */
public class MainActivity extends Activity {
    TextView tvShow;
    private int i = 0;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tvShow = (TextView) findViewById(R.id.textView1);
        new Thread(new ThreadShow()).start();
    }

    // handler类接收数据
    Handler handler = new Handler() {
        public void handleMessage(Message msg) {
            if (msg.what == 1) {
                tvShow.setText(Integer.toString(i++));
                System.out.println("receive....");
            }
        };
    };

    // 线程类
    class ThreadShow implements Runnable {

        @Override
        public void run() {
            // TODO Auto-generated method stub
            while (true) {
                try {
                    Thread.sleep(1000);   //每隔一秒执行一次
                    Message msg = new Message();
                    msg.what = 1;
                    handler.sendMessage(msg);
                    System.out.println("send...");
                } catch (Exception e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                    System.out.println("thread error...");
                }
            }
        }
    }
}

2、方法二:Handler类自带的postDelyed

其中使用PostDelayed方法，1秒后调用此Runnable对象
handler.postDelayed(runnable, 1000); 实际上也就实现了一个1s的一个定时器

如果想要关闭此定时器，可以这样操作
handler.removeCallbacks(runnable);

package com.example.yuyin_lixian;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.widget.TextView;  

/**
 * handler定时器使用postDelyed实现
 *
 * @author Smalt
 *
 */
public class MainActivity extends Activity {
    TextView tvShow;
    private int i = 0;
    private int TIME = 1000;  

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tvShow = (TextView) findViewById(R.id.textView1);
        handler.postDelayed(runnable, TIME); //每隔1s执行
    }  

    Handler handler = new Handler();
    Runnable runnable = new Runnable() {  

        @Override
        public void run() {
            // handler自带方法实现定时器
            try {
                handler.postDelayed(this, TIME);
                tvShow.setText(Integer.toString(i++));
                System.out.println("do...");
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
                System.out.println("exception...");
            }
        }
    };  

}

3、方法二:Handler+Timer+TimerTask

package com.example.yuyin_lixian;

import java.util.Timer;
import java.util.TimerTask;  

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.widget.TextView;  

/**
 * 定时器实现:Handler+Timer+TimerTask
 *
 * @author Smalt
 *
 */
public class MainActivity extends Activity {
    TextView tvShow;
    private int i = 0;
    private int TIME = 1000;  

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tvShow = (TextView) findViewById(R.id.textView1);
        timer.schedule(task, 1000, 1000); // 1s后执行task,经过1s再次执行
    }  

    Handler handler = new Handler() {
        public void handleMessage(Message msg) {
            if (msg.what == 1) {
                tvShow.setText(Integer.toString(i++));
            }
            super.handleMessage(msg);
        };
    };
    Timer timer = new Timer();
    TimerTask task = new TimerTask() {  

        @Override
        public void run() {
            // 需要做的事:发送消息
            Message message = new Message();
            message.what = 1;
            handler.sendMessage(message);
        }
    };
}