Android AsyncTask實現一個執行緒操作完成後啟動另一個執行緒
如何在一個執行緒完成操作後執行另一個執行緒？
有時候我們需要等待一個執行緒執行完成後再執行下一個執行緒。
發現asynctask可以實現這個功能，可以在一個執行緒操作完成後執行下一個執行緒。
原理就不多說了，直接看程式碼：
實現下載三個網路圖片，第一幅圖片下載完成後接著下載第二個圖片，第二個圖片下載完成後接著下載第三個圖片。
public class AsyncTaskTest extends Activity {
private Button button01;
private ImageView imageView01,imageView02,imageView03;
private ProgressDialog progressDialog01,progressDialog02,progressDialog03;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.async_task);
button01=(Button)findViewById(R.id.button01);
imageView01=(ImageView)findViewById(R.id.imageview01);
imageView02=(ImageView)findViewById(R.id.imageview02);
imageView03=(ImageView)findViewById(R.id.imageview03);
progressDialog01=new ProgressDialog(this);
progressDialog02=new ProgressDialog(this);
progressDialog03=new ProgressDialog(this);
button01.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
DownloadImagTask01 task01=new DownloadImagTask01();
task01.execute(url01);
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.async_task_test, menu);
return true;
}
private class DownloadImagTask01 extends AsyncTask<String, Void, Bitmap>{
@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
super.onPreExecute();
progressDialog01.setTitle("圖片01下載提示");
progressDialog01.setMessage("圖片01正在下載中");
progressDialog01.show();
}
@Override
protected Bitmap doInBackground(String... params) {
// TODO Auto-generated method stub
Bitmap bitmap=null;
try {
URL url=new URL(params[0]);
HttpURLConnection connection=(HttpURLConnection)url.openConnection();
connection.setDoInput(true);
connection.connect();
InputStream inputStream=connection.getInputStream();
bitmap=BitmapFactory.decodeStream(inputStream);
inputStream.close();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return bitmap;
}
protected void onPostExecute(Bitmap result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
imageView01=(ImageView)findViewById(R.id.imageview01);
imageView01.setImageBitmap(result);
DownloadImagTask02 task02=new DownloadImagTask02();
progressDialog01.dismiss();
task02.execute(url02);
}
}
private class DownloadImagTask02 extends AsyncTask<String, Void, Bitmap>{
@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
super.onPreExecute();
progressDialog02.setTitle("圖片02下載提示");
progressDialog02.setMessage("圖片02正在下載中");
progressDialog02.show();
}
@Override
protected Bitmap doInBackground(String... params) {
// TODO Auto-generated method stub
Bitmap bitmap=null;
try {
URL url=new URL(params[0]);
HttpURLConnection connection=(HttpURLConnection)url.openConnection();
connection.setDoInput(true);
connection.connect();
InputStream inputStream=connection.getInputStream();
bitmap=BitmapFactory.decodeStream(inputStream);
inputStream.close();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return bitmap;
}
protected void onPostExecute(Bitmap result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
imageView02.setImageBitmap(result);
progressDialog02.dismiss();
DownloadImagTask03 task03=new DownloadImagTask03();
task03.execute(url03);
}
}
private class DownloadImagTask03 extends AsyncTask<String, Void, Bitmap>{
@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
super.onPreExecute();
progressDialog03.setTitle("圖片03下載提示");
progressDialog03.setMessage("圖片03正在下載中");
progressDialog03.show();
}
@Override
protected Bitmap doInBackground(String... params) {
// TODO Auto-generated method stub
Bitmap bitmap=null;
try {
URL url=new URL(params[0]);
HttpURLConnection connection=(HttpURLConnection)url.openConnection();
connection.setDoInput(true);
connection.connect();
InputStream inputStream=connection.getInputStream();
bitmap=BitmapFactory.decodeStream(inputStream);
inputStream.close();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return bitmap;
}
protected void onPostExecute(Bitmap result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
imageView03.setImageBitmap(result);
progressDialog03.dismiss();
}
}
}
佈局檔案內容為：
<ScrollView 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">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical"
>
<Button
android:id="@+id/button01"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="開始下載圖片"
/>
<ImageView
android:id="@+id/imageview01"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>
<ImageView
android:id="@+id/imageview02"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>
<ImageView
android:id="@+id/imageview03"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>
</LinearLayout>
</ScrollView>
注意新增網路許可權
<uses-permission android:name="android.permission.INTERNET"></uses-permission>