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:
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:
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:
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<String,Integer,Bitmap> {//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 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