android异步的几种方式
16lz
2022-04-12
android异步处理的几种方式
1,对数据库uri查询的异步方式----AsyncQueryHandler示例
首先写一个AsyncQueryHandler继承类QueryHandler,然后
new一个mQueryHandler对象。查询完了之后会回调onQueryComplete函数,如下:
Java代码
- private void query() {
- Uri uri = Sms.CONVESATION_URI;
- mQueryHandler.startQuery(0, null, uri, CONVERSATION_PROJECTION, null, null, "sms.date desc");
- }
- // 写一个异步查询类
- private final class QueryHandler extends AsyncQueryHandler {
- public QueryHandler(ContentResolver cr) {
- super(cr);
- }
- @Override
- protected void onQueryComplete(int token, Object cookie, Cursor cursor) {
- super.onQueryComplete(token, cookie, cursor);
- // 更新mAdapter的Cursor
- mAdapter.changeCursor(cursor);
- }
- }
2,使用Thread+Handler实现非UI线程更新UI界面
示例如下:
Java代码
- public class ThreadHandlerActivity extends Activity {
- /** Called when the activity is first created. */
- private static final int MSG_SUCCESS = 0;//获取图片成功的标识
- private static final int MSG_FAILURE = 1;//获取图片失败的标识
- private ImageView mImageView;
- private Button mButton;
- private Thread mThread;
- private Handler mHandler = new Handler() {
- public void handleMessage (Message msg) {//此方法在ui线程运行
- switch(msg.what) {
- case MSG_SUCCESS:
- mImageView.setImageBitmap((Bitmap) msg.obj);//imageview显示从网络获取到的logo
- Toast.makeText(getApplication(), getApplication().getString(R.string.get_pic_success), Toast.LENGTH_LONG).show();
- break;
- case MSG_FAILURE:
- Toast.makeText(getApplication(), getApplication().getString(R.string.get_pic_failure), Toast.LENGTH_LONG).show();
- break;
- }
- }
- };
- @Override
- public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- mImageView= (ImageView) findViewById(R.id.imageView);//显示图片的ImageView
- mButton = (Button) findViewById(R.id.button);
- mButton.setOnClickListener(new OnClickListener() {
- @Override
- public void onClick(View v) {
- if(mThread == null) {
- mThread = new Thread(runnable);
- mThread.start();//线程启动
- }
- else {
- Toast.makeText(getApplication(), getApplication().getString(R.string.thread_started), Toast.LENGTH_LONG).show();
- }
- }
- });
- }
- Runnable runnable = new Runnable() {
- @Override
- public void run() {//run()在新的线程中运行
- HttpClient hc = new DefaultHttpClient();
- HttpGet hg = new HttpGet("http://csdnimg.cn/www/images/csdnindex_logo.gif");//获取csdn的logo
- final Bitmap bm;
- try {
- HttpResponse hr = hc.execute(hg);
- bm = BitmapFactory.decodeStream(hr.getEntity().getContent());
- } catch (Exception e) {
- mHandler.obtainMessage(MSG_FAILURE).sendToTarget();//获取图片失败
- return;
- }
- mHandler.obtainMessage(MSG_SUCCESS,bm).sendToTarget();//获取图片成功,向ui线程发送MSG_SUCCESS标识和bitmap对象
- // mImageView.setImageBitmap(bm); //出错!不能在非ui线程操作ui元素
- // mImageView.post(new Runnable() {//另外一种更简洁的发送消息给ui线程的方法。
- //
- // @Override
- // public void run() {//run()方法会在ui线程执行
- // mImageView.setImageBitmap(bm);
- // }
- // });
- }
- };
- }
3,使用AsyncTask异步更新UI界面
AsyncTask抽象出后台线程运行的五个状态,分别是:1、准备运行,2、正在后台运行,3、进度更新,4、完成后台任务,5、取消任务,对于这五个阶段,AsyncTask提供了五个回调函数:
1、准备运行:onPreExecute(),该回调函数在任务被执行之后立即由UI线程调用。这个步骤通常用来建立任务,在用户接口(UI)上显示进度条。
2、正在后台运行:doInBackground(Params...),该回调函数由后台线程在onPreExecute()方法执行结束后立即调用。通常在这里执行耗时的后台计算。计算的结果必须由该函数返回,并被传递到onPostExecute()中。在该函数内也可以使用publishProgress(Progress...)来发布一个或多个进度单位(unitsof progress)。这些值将会在onProgressUpdate(Progress...)中被发布到UI线程。
3. 进度更新:onProgressUpdate(Progress...),该函数由UI线程在publishProgress(Progress...)方法调用完后被调用。一般用于动态地显示一个进度条。
4. 完成后台任务:onPostExecute(Result),当后台计算结束后调用。后台计算的结果会被作为参数传递给这一函数。
5、取消任务:onCancelled (),在调用AsyncTask的cancel()方法时调用
示例代码:
Java代码
- public class AsyncTaskActivity extends Activity {
- private ImageView mImageView;
- private Button mButton;
- private ProgressBar mProgressBar;
- @Override
- public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- mImageView= (ImageView) findViewById(R.id.imageView);
- mButton = (Button) findViewById(R.id.button);
- mProgressBar = (ProgressBar) findViewById(R.id.progressBar);
- mButton.setOnClickListener(new OnClickListener() {
- @Override
- public void onClick(View v) {
- GetCSDNLogoTask task = new GetCSDNLogoTask();
- task.execute("http://csdnimg.cn/www/images/csdnindex_logo.gif");
- }
- });
- }
- class GetCSDNLogoTask extends AsyncTask
{//继承AsyncTask - @Override
- protected Bitmap doInBackground(String... params) {//处理后台执行的任务,在后台线程执行
- publishProgress(0);//将会调用onProgressUpdate(Integer... progress)方法
- HttpClient hc = new DefaultHttpClient();
- publishProgress(30);
- HttpGet hg = new HttpGet(params[0]);//获取csdn的logo
- final Bitmap bm;
- try {
- HttpResponse hr = hc.execute(hg);
- bm = BitmapFactory.decodeStream(hr.getEntity().getContent());
- } catch (Exception e) {
- return null;
- }
- publishProgress(100);
- //mImageView.setImageBitmap(result); 不能在后台线程操作ui
- return bm;
- }
- protected void onProgressUpdate(Integer... progress) {//在调用publishProgress之后被调用,在ui线程执行
- mProgressBar.setProgress(progress[0]);//更新进度条的进度
- }
- protected void onPostExecute(Bitmap result) {//后台任务执行完之后被调用,在ui线程执行
- if(result != null) {
- Toast.makeText(AsyncTaskActivity.this, "成功获取图片", Toast.LENGTH_LONG).show();
- mImageView.setImageBitmap(result);
- }else {
- Toast.makeText(AsyncTaskActivity.this, "获取图片失败", Toast.LENGTH_LONG).show();
- }
- }
- protected void onPreExecute () {//在 doInBackground(Params...)之前被调用,在ui线程执行
- mImageView.setImageBitmap(null);
- mProgressBar.setProgress(0);//进度条复位
- }
- protected void onCancelled () {//在ui线程执行
- mProgressBar.setProgress(0);//进度条复位
- }
- }
- }
下面是对应的xml
Xml代码
- <?xml version="1.0" encoding="utf-8"?>
- <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
- android:orientation="vertical" android:layout_width="fill_parent"
- android:layout_height="fill_parent">
- <ProgressBar android:layout_width="fill_parent" android:layout_height="wrap_content" android:id="@+id/progressBar" style="?android:attr/progressBarStyleHorizontal">ProgressBar>
- <Button android:id="@+id/button" android:text="下载图片" android:layout_width="wrap_content" android:layout_height="wrap_content">Button>
- <ImageView android:id="@+id/imageView" android:layout_height="wrap_content"
- android:layout_width="wrap_content" />
- LinearLayout>
具体的AsyncTask的实现原理可以参考
http://blog.csdn.net/mylzc/article/details/6774131
另外对于handler机制的详细解析,可以参考下面
http://blog.csdn.net/mylzc/article/details/6771331
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