Android 异步加载图片-AsyncTask
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。
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。view plaincopy to clipboardprint?
一切说明都在代码中......................................................
Activity
- /*
- * Android 异步任务AsyncTask
- * AsyncTask定义了三种泛型类,Params,Progress,Result
- */
- package rw.ansync;
- import android.app.Activity;
- import android.os.Bundle;
- import android.view.View;
- import android.view.View.OnClickListener;
- import android.widget.Button;
- import android.widget.EditText;
- import android.widget.ImageView;
- import android.widget.ProgressBar;
- public class AsynaTask_TestActivity extends Activity {
- /** Called when the activity is first created. */
- private EditText editText;
- private Button button;
- private ProgressBar progressBar;
- private ImageView imageView;
- private static final String URL_STRING="http://photocdn.sohu.com/20110927/Img320705637.jpg";
- @Override
- public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- editText=(EditText) findViewById(R.id.editText1);
- editText.setText(URL_STRING);
- button=(Button) findViewById(R.id.button1);
- progressBar=(ProgressBar) findViewById(R.id.progressBar1);
- imageView=(ImageView) findViewById(R.id.imageView1);
- button.setOnClickListener(new ButtonListener());
- }
- class ButtonListener implements OnClickListener{
- @Override
- public void onClick(View v) {
- // TODO Auto-generated method stub
- MyAsynaTask mTask=new MyAsynaTask(imageView, progressBar,button);
- mTask.execute(URL_STRING);
- }
- }
- }
MyAsynaTask.java
- package rw.ansync;
- import java.io.InputStream;
- import java.net.HttpURLConnection;
- import java.net.URL;
- import android.R.integer;
- import android.graphics.Bitmap;
- import android.graphics.BitmapFactory;
- import android.os.AsyncTask;
- import android.widget.Button;
- import android.widget.ImageView;
- import android.widget.ProgressBar;
- public class MyAsynaTask extends AsyncTask<String, Integer, Bitmap>{
- private ImageView imageView;
- private ProgressBar progressBar;
- private Button button;
- public MyAsynaTask( ImageView imageView,
- ProgressBar progressBar,Button button) {
- super();
- this.imageView = imageView;
- this.progressBar = progressBar;
- this.button=button;
- }
- @Override
- protected void onPreExecute() {
- // TODO Auto-generated method stub
- /*
- * 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
- * Toast.makeText(context, "准备下载", Toast.LENGTH_LONG).show();
- */
- super.onPreExecute();
- }
- @Override
- 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
- // TODO Auto-generated method stub
- /*
- * 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
- */
- Bitmap bitmap=null;
- try {
- URL url=new URL(params[0]);
- HttpURLConnection connection=(HttpURLConnection) url.openConnection();
- connection.setDoInput(true);
- connection.connect();
- progressBar.setMax(connection.getContentLength());
- InputStream inputStream=connection.getInputStream();
- bitmap=BitmapFactory.decodeStream(inputStream);
- // inputStream.close();
- /*
- * 以下完全为了演示进度条,如果为了显示进度条可以把这个去掉
- */
- /*
- byte []buf=new byte[1024*4];
- inputStream=connection.getInputStream();
- int len=0;
- while ((inputStream.read(buf))!=-1) {
- len+=buf.length;
- publishProgress(len);
- }
- */
- inputStream.close();
- } catch (Exception e) {
- // TODO: handle exception
- }
- return bitmap;
- }
- @Override
- protected void onProgressUpdate(Integer... values) {
- // TODO Auto-generated method stub
- /*
- * 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
- */
- int value=values[0];
- progressBar.setProgress(value);
- super.onProgressUpdate(values);
- }
- @Override
- protected void onPostExecute(Bitmap result) {
- // TODO Auto-generated method stub
- /*
- * 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
- */
- imageView.setImageBitmap(result);
- button.setText("下载完成");
- super.onPostExecute(result);
- }
- }
加上权限<uses-permission android:name="android.permission.INTERNET"></uses-permission>
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