Android 异步加载图片AsyncTask

AsyncTask定义了三种泛型类型 Params，Progress和Result。
    •Params 启动任务执行的输入参数，比如HTTP请求的URL。
    •Progress 后台任务执行的百分比。
    •Result 后台执行任务最终返回的结果，比如String。
Activity

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/*

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 * Android 异步任务AsyncTask

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 * AsyncTask定义了三种泛型类,Params,Progress,Result

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 */

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package rw.ansync;

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import android.app.Activity;

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import android.os.Bundle;

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import android.view.View;

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import android.view.View.OnClickListener;

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import android.widget.Button;

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import android.widget.EditText;

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import android.widget.ImageView;

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import android.widget.ProgressBar;

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public class AsynaTask_TestActivity extends Activity {

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    /** Called when the activity is first created. */

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    private EditText editText;

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    private Button button;

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    private ProgressBar progressBar;

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    private ImageView imageView;

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    private static final String URL_STRING="http://photocdn.sohu.com/20110927/Img320705637.jpg";

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    @Override

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    public void onCreate(Bundle savedInstanceState) {

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        super.onCreate(savedInstanceState);

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        setContentView(R.layout.main);

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        editText=(EditText) findViewById(R.id.editText1);

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        editText.setText(URL_STRING);

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        button=(Button) findViewById(R.id.button1);

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        progressBar=(ProgressBar) findViewById(R.id.progressBar1);

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        imageView=(ImageView) findViewById(R.id.imageView1);

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        button.setOnClickListener(new ButtonListener());

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    }

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    class ButtonListener implements OnClickListener{

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        @Override

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        public void onClick(View v) {

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            // TODO Auto-generated method stub

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                MyAsynaTask mTask=new MyAsynaTask(imageView, progressBar,button);

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                mTask.execute(URL_STRING);

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        }

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    }

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}

MyAsynaTask.java

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package rw.ansync;

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import java.io.ByteArrayOutputStream;

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import java.io.File;

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import java.io.FileOutputStream;

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import java.io.InputStream;

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import java.io.OutputStream;

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import java.net.HttpURLConnection;

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import java.net.URL;

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import android.R.integer;

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import android.graphics.Bitmap;

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import android.graphics.BitmapFactory;

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import android.os.AsyncTask;

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import android.os.IInterface;

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import android.util.Log;

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import android.widget.Button;

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import android.widget.ImageView;

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import android.widget.ProgressBar;

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public class MyAsynaTask extends AsyncTask<string, bitmap="" integer,="">{

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    private ImageView imageView;

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    private ProgressBar progressBar;

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    private Button button;

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    public MyAsynaTask( ImageView imageView,

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            ProgressBar progressBar,Button button) {

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        super();

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        this.imageView = imageView;

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        this.progressBar = progressBar;

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        this.button=button;

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    }

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    @Override

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    protected void onPreExecute() {

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        // TODO Auto-generated method stub

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        /*

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         * 改方法在执行实际的后台操作时被UI线程调用，可以在该方法中做一些准备工作，比如

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         *  Toast.makeText(context, "准备下载", Toast.LENGTH_LONG).show();

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         */

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        super.onPreExecute();

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    }

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    @Override

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    protected Bitmap doInBackground(String... params) {//输入编变长的可变参数 和ＵＩ线程中的Asyna.execute()对应

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        // TODO Auto-generated method stub

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    /*

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     * 该方法在OnpreExecute执行以后马上执行，改方法执行在后台线程当中，负责耗时的计算，可以调用publishProcess方法来实时更新任务进度

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     */

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        Bitmap bitmap=null;

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        try {

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             URL url=new URL(params[0]);

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             Log.i("------------->", url+"");

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             HttpURLConnection connection=(HttpURLConnection) url.openConnection();

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             connection.connect();

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             int MAX=connection.getContentLength();

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             progressBar.setMax(MAX);

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             InputStream inputStream=connection.getInputStream();

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             ByteArrayOutputStream outputStream=new ByteArrayOutputStream();

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             /*

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              * 为了显示进度条，每接受1024字节要求更新一次ＵＩ，为了看效果

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              */

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             byte []buf=new byte[1024];

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             int len = 0;

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             int processBarNum=0;

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             while( (len=inputStream.read(buf))!=-1){

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                 outputStream.write(buf, 0, len);

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                 processBarNum+=len;

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                 publishProgress(processBarNum);//通知要更新processBar

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             }

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             bitmap=BitmapFactory.decodeByteArray(outputStream.toByteArray(),0, MAX);

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             inputStream.close();

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        } catch (Exception e) {

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            // TODO: handle exception

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        }

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        return bitmap;

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    }

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    @Override

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    protected void onProgressUpdate(Integer... values) {

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        // TODO Auto-generated method stub

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        /*

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         * 当publichProcess 呗调用以后，ＵＩ线程将调用这个有方法在界面上展示任务的情况，比如一个额进度条。这里是更新进度条

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         */

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        int value=values[0];

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        progressBar.setProgress(value);

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        super.onProgressUpdate(values);

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    }

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    @Override

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    protected void onPostExecute(Bitmap result) {

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        // TODO Auto-generated method stub

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        /*

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         * 在doInbackground执行完成以后，onPostExecute将被调用，后台的结果将返回给UI线程，将获得图片显示出来

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         */

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        imageView.setImageBitmap(result);

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        super.onPostExecute(result);

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    }

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}</string,>

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

Android 异步加载图片-AsyncTask

转自：http://blog.csdn.net/rwyz1314/article/details/6841639