Android之Handler的使用-优快云博客

本文通过两个示例介绍了Android中Handler的基本用法。示例一展示如何使用Handler更新UI进度条；示例二则演示了如何利用Handler配合ProgressDialog进行长时间任务处理，并在任务完成后关闭提示框。

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Handler的使用：

由于Handler运行在主线程中（UI线程），它与子线程可以通过Message对象来传递数据。

Handler的作用：

1.安排消息或Runnable在某个主线程中某个地方执行。

2.安排一个动作在不同的线程中执行。

代码一、

package com.ko8e;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;

public class MyActivity extends Activity {
    /** Called when the activity is first created. */
    private ProgressBar progressbar = null;
    private Button button = null;
	
	@Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    
        progressbar = (ProgressBar) findViewById(R.id.progressbar);
        button = (Button) findViewById(R.id.button);
        
        button.setOnClickListener(new Button.OnClickListener() {
			public void onClick(View v) {
				progressbar.setVisibility(View.VISIBLE);
				handler.post(runnable);
			}});
	}

	Handler handler = new Handler() {
		@Override
		public void handleMessage(Message msg) {
			progressbar.setProgress(msg.arg1);
			super.handleMessage(msg);
		}
	};
	
	private Runnable runnable = new Runnable() {
		int i = 0;
		public void run() {
			// TODO Auto-generated method stub
			i = i + 10;
			Message msg = handler.obtainMessage();
			msg.arg1 = i;
			handler.sendMessage(msg);
			if(i == progressbar.getMax()) {
				handler.removeCallbacks(runnable);
				progressbar.setVisibility(View.GONE);
			}
		}
	};
}

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"
    >
<ProgressBar
	android:id="@+id/progressbar"
	android:layout_width="fill_parent"
	android:layout_height="wrap_content"
	android:visibility="gone"
	style="?android:attr/progressBarStyleHorizontal"
	/>
<Button
	android:id="@+id/button"
	android:layout_width="wrap_content"
	android:layout_height="wrap_content"
	android:text="button"
	/>
</LinearLayout>

代码二、

package com.mnkjxy;

import android.app.Activity;
import android.app.ProgressDialog;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class MyActivity extends Activity {

	private Button button = null;
	private ProgressDialog dialog = null;

	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);

		button = (Button) findViewById(R.id.button);
		button.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				processThread();
			}
		});
	}

	private Handler handler = new Handler() {
		@Override
		public void handleMessage(Message msg) {
			super.handleMessage(msg);
			// 程序运行到这里关闭
			dialog.dismiss();
		}
	};

	public void processThread() {
		dialog = ProgressDialog.show(MyActivity.this, "正在下载资源", "请稍等···");
		new Thread() {
			public void run() {
				longTimeWait();
				handler.sendEmptyMessage(0);
			}
		}.start();
	}

	public void longTimeWait() {
		try {
			Thread.sleep(10000);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}

}

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"
    >
<TextView  
	android:id="@+id/view"
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/hello"
    />
<Button
	android:id="@+id/button"
	android:layout_width="wrap_content"
	android:layout_height="wrap_content"
	android:text="@string/button"
	/>    
</LinearLayout>