AsyncTask简单实例

public class MainActivity extends ActionBarActivity {

private Button button;

private Button button2;

[code]@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    button = (Button) findViewById(R.id.button);
    button2 = (Button) findViewById(R.id.button2);
    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(MainActivity.this, AsyncTaskActivity.class);
            startActivity(intent);
        }
    });
    button2.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(MainActivity.this, GetImageAsyncTaskActivity.class);
            startActivity(intent);
        }
    });
}

}

[code]public class GetImageAsyncTaskActivity extends Activity {

    private ImageView imageView;
    private ProgressBar progressBar;
    private MyAsyncTask myAsyncTask;
    private static String URL = "http://www.logoing.net/wp-content/uploads/2012/08/baidulogo1.jpg";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.getimage);
        imageView = (ImageView) findViewById(R.id.imageView);
        progressBar = (ProgressBar) findViewById(R.id.progressBar2);
        myAsyncTask=new MyAsyncTask();
        myAsyncTask.execute(URL);
    }

    class MyAsyncTask extends AsyncTask<String, Void, Bitmap> {

        @Override
        protected void onPreExecute() {//doInBackgroud方法前执行
            super.onPreExecute();
            progressBar.setVisibility(View.VISIBLE);//设置滚动条可见
        }

        @Override
        protected void onPostExecute(Bitmap bitmap) {//doInBackgroud方法后执行
            super.onPostExecute(bitmap);
            progressBar.setVisibility(View.GONE);//设置滚动条不可见
            imageView.setImageBitmap(bitmap);//任务执行完，设置图片
        }

        @Override
        protected Bitmap doInBackground(String... params) {
            Bitmap bitmap = null;
            URLConnection connection;
            InputStream inputStream;
            try {
                Thread.sleep(3000);//模拟耗时操作
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            try {
                connection = new URL(params[0]).openConnection();
                inputStream = connection.getInputStream();
                BufferedInputStream bufferedInputStream = new BufferedInputStream(inputStream);
                bitmap = BitmapFactory.decodeStream(bufferedInputStream);
                inputStream.close();
                bufferedInputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return bitmap;
        }
    }
}

[code]public class AsyncTaskActivity extends Activity {

    private ProgressBar progressBar;
    private MyAsyncTask myAsyncTask;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.progressbar);
        progressBar = (ProgressBar) findViewById(R.id.progressBar);
        myAsyncTask=new MyAsyncTask();
        myAsyncTask.execute();
    }

    @Override
    protected void onPause() {
        super.onPause();
        if (myAsyncTask != null && myAsyncTask.getStatus() == AsyncTask.Status.RUNNING) {
            myAsyncTask.cancel(true);//设置取消，但不会终止线程
        }
    }

    class MyAsyncTask extends AsyncTask<Void, Integer, Void> {

        @Override
        protected Void doInBackground(Void... params) {
            for (int i = 0; i < 100; i++) {
                if (myAsyncTask.isCancelled()) {
                    break;//如果取消状态，跳出循环
                }
                onProgressUpdate(i);
                try {
                    Thread.sleep(300);//模拟耗时操作
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            return null;
        }

        @Override
        protected void onProgressUpdate(Integer... values) {
            super.onProgressUpdate(values);
            if (myAsyncTask.isCancelled()) {
                return;//如果取消状态，返回
            }
            progressBar.setProgress(values[0]);
        }
    }
}

activity_main.xml

[code]<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <Button
        android:id="@+id/button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="click to progressbar" />

    <Button
        android:id="@+id/button2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="click to getImage" />
</LinearLayout>

getimage.xml

[code]<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent" android:layout_height="match_parent">
    <ImageView
        android:id="@+id/imageView"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
    <ProgressBar
        style="?android:attr/progressBarStyleLarge"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/progressBar2"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true" />
</RelativeLayout>

progressbar.xml

[code]<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="10dp">
    <ProgressBar
        android:id="@+id/progressBar"
        style="?android:attr/progressBarStyleHorizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical" />
</LinearLayout>

参考：慕课网