android多线程使用实例之AsynTask和handler的使用

在android开发当中，主线程（UI线程）是不允许处理复杂的耗时操作的，否则会导致UI线程阻塞，因此对此类操作应该使用子线程处理，一般会使用到AsyncTask异步任务和handler多线程来处理，并且在子线程中是不允许修改UI线程元素的，因此会使用到异步回调方法；下面例子通过AsyncTask和handler例子说明；

首先建立布局文件activity_main.xml,分别定义下载按钮和获取信息按钮

<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="com.example.picdown.MainActivity" >

<ImageView
android:id="@+id/iv"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
/>

<Button
android:id="@+id/btn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="下载" />

<Button
android:id="@+id/testbtn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="测试线程"
/>

</LinearLayout>

该例子是关于图片的，新建一个实体类Pic.java

package com.example.picdown;

public class Pic {

private String name;
private String url;
private String type;

Pic(String name,String url,String type){
setName(name);
setUrl(url);
setType(type);
}

public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}

}

回到MainActivity当中实现下载功能和图片信息获取功能：

package com.example.picdown;

import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

import android.animation.ArgbEvaluator;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.DialogInterface;
import android.content.DialogInterface.OnCancelListener;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;

public class MainActivity extends Activity implements OnClickListener{
private Button btn,testbtn;
private ImageView iv;
private ProgressDialog mProgressDialog;
private DownloadAsyncTask mTask;
private static final String PATH = "http://www.baidu.com/img/bdlogo.png";
private Handler handler;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initView();
}

public void initView(){

btn =(Button) findViewById(R.id.btn);
testbtn=(Button) findViewById(R.id.testbtn);
iv=(ImageView) findViewById(R.id.iv);

btn.setOnClickListener(this);
testbtn.setOnClickListener(this);
//初始化handler对象

handler =new Handler(){
@Override
public void handleMessage(Message msg) {
if(msg.what==1){
Pic pic =(Pic) msg.obj;
String name =pic.getName();
String url= pic.getUrl();
String type =pic.getType();
System.out.println("图片名："+name+"；图片地址："+url+"；图片类型："+type);
Toast.makeText(getApplicationContext(), "图片名："+name+"；图片地址："+url+"；图片类型："+type, Toast.LENGTH_SHORT).show();
}
}
};
}

public void onClick(View v) {

switch (v.getId()) {
case R.id.btn:
downImg();
break;

case R.id.testbtn:
new Thread(new Runnable(){

public void run() {

Pic pics =new Pic("百度logo",PATH,"jpg图片");
Message msg =handler.obtainMessage();
msg.what=1;
msg.obj=pics;
handler.sendMessage(msg);

}}).start();

break;
}

}

private void  downImg(){
// 执行异步线程
mTask = new DownloadAsyncTask();
mTask.execute(PATH);
}

private class DownloadAsyncTask extends AsyncTask<String, Integer, Bitmap>{

@Override
protected Bitmap doInBackground(String... params) {

Bitmap bitmap =null;
try{
URL url = new URL(params[0]);
HttpURLConnection con =(HttpURLConnection) url.openConnection();
con.setDoInput(true);
con.connect();
InputStream inputstream =con.getInputStream();
bitmap=BitmapFactory.decodeStream(inputstream);
inputstream.close();

}catch(Exception e){

e.printStackTrace();

}

return bitmap;
}

@Override
protected void onPostExecute(Bitmap result) {
super.onPostExecute(result);
iv.setImageBitmap(result);//设置图片

}

}

}

最后不要忘了在AndroidManifest.xml当中添加访问网络的权限

<uses-permission android:name="android.permission.INTERNET"/>

实现效果：