异步获取已安装程序列表（PackageManager+AsyncTask）

文章出处：http://gundumw100.iteye.com/blog/1067414

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AsyncTask是抽象类.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的执行分为四个步骤，每一步都对应一个回调方法，这些方法不应该由应用程序调用，开发者需要做的就是实现这些方法。?
onPreExecute(), 该方法将在执行实际的后台操作前被UI thread调用。可以在该方法中做一些准备工作，如在界面上显示一个进度条。?
doInBackground(Params...), 将在onPreExecute 方法执行后马上执行，该方法运行在后台线程中。这里将主要负责执行那些很耗时的后台计算工作。可以调用 publishProgress方法来更新实时的任务进度。该方法是抽象方法，子类必须实现。?
onProgressUpdate(Progress...),在publishProgress方法被调用后，UI thread将调用这个方法从而在界面上展示任务的进展情况，例如通过一个进度条进行展示。?
onPostExecute(Result), 在doInBackground 执行完成后，onPostExecute 方法将被UI thread调用，后台的计算结果将通过该方法传递到UI thread.?
为了正确的使用AsyncTask类，以下是几条必须遵守的准则：?
1) Task的实例必须在UI thread中创建?
2) execute方法必须在UI thread中调用?
3) 不要手动的调用onPreExecute(), onPostExecute(Result)，doInBackground(Params...), onProgressUpdate(Progress...)这几个方法?
4) 该task只能被执行一次，否则多次调用时将会出现异常?

下面是AsyncTask异步获取已安装程序列表的例子：?

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public class Screen1 extends Activity{      private static final String tag="Screen1";      private ListView listview;      private Context mContext;      private List<ResolveInfo> list;      private AppAdapter adapter;      private PackageManager pm;      @Override      protected void onCreate(Bundle savedInstanceState) {          // TODO Auto-generated method stub          super.onCreate(savedInstanceState);          //给Activity注册界面进度条功能          requestWindowFeature(Window.FEATURE_INDETERMINATE_PROGRESS);          setContentView(R.layout.screen_1);          mContext = this;                    list=new ArrayList<ResolveInfo>();          pm = mContext.getPackageManager();          listview = (ListView)findViewById(R.id.listview);                    adapter = new AppAdapter(mContext);                    listview.setAdapter(adapter);          listview.setOnItemClickListener(new AdapterView.OnItemClickListener() {                @Override              public void onItemClick(AdapterView<?> parent, View view,                      int position, long id) {                  // TODO Auto-generated method stub                  Log.i(tag, "---------------onItemClick-----------------");                  ResolveInfo info=list.get(position);                  String packageName = info.activityInfo.packageName;                  String className = info.activityInfo.name;                    Intent intent = new Intent();                  intent.setClassName(packageName, className);                  startActivity(intent);              }          });          new MyTask().execute();                }          class AppAdapter extends BaseAdapter{          Context context;          AppAdapter(Context context){              this.context=context;          }          @Override          public int getCount() {              // TODO Auto-generated method stub              return list.size();          }            @Override          public Object getItem(int position) {              // TODO Auto-generated method stub              return list.get(position);          }            @Override          public long getItemId(int position) {              // TODO Auto-generated method stub              return position;          }            @Override          public View getView(int position, View convertView, ViewGroup parent) {              // TODO Auto-generated method stub              if(convertView==null){                  LayoutInflater inflater=getLayoutInflater().from(context);                  convertView=inflater.inflate(R.layout.simple_item_2, null);              }              ImageView iv=(ImageView)convertView.findViewById(R.id.icon);              TextView tv=(TextView)convertView.findViewById(R.id.text);                            ResolveInfo info=list.get(position);              iv.setBackgroundDrawable(info.activityInfo.loadIcon(pm));              tv.setText(info.activityInfo.loadLabel(pm));              return convertView;          }                }            class MyTask extends AsyncTask<String, Integer, String>{            @Override          protected void onPreExecute() {              setProgressBarIndeterminateVisibility(true);              showProgress();          }            @Override          protected void onPostExecute(String param) {              setProgressBarIndeterminateVisibility(false);              adapter.notifyDataSetChanged();              closeProgress();          }            @Override          protected void onCancelled() {              // TODO Auto-generated method stub              super.onCancelled();          }            @Override          protected void onProgressUpdate(Integer... values) {              // TODO Auto-generated method stub              super.onProgressUpdate(values);          }            @Override          protected String doInBackground(String... params) {              // TODO Auto-generated method stub              // 获取已经安装程序列表              Intent intent = new Intent(Intent.ACTION_MAIN, null);              intent.addCategory(Intent.CATEGORY_LAUNCHER);              list = pm.queryIntentActivities(intent, 0);              Collections.sort(list, new ResolveInfo.DisplayNameComparator(pm));              return null;          }                }            private Dialog      dialog;      protected void showProgress() {          if(dialog == null) {              dialog =  new Dialog(this, R.style.Theme_TransparentDialog);  //          dialog.setContentView(R.layout.progress_dialog);              dialog.setContentView(new ProgressBar(this));              dialog.setCancelable(true);              dialog.show();          }      }      //      protected void closeProgress() {                    if(dialog != null) {              dialog.cancel();              dialog = null;          }      }      public boolean isShowing(){          if(dialog != null) {              return dialog.isShowing();          }          return false;      }        }  

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simple_item_2.xml?

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<?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"      >      <TextView        android:layout_width="fill_parent"       android:layout_height="wrap_content"       android:text="应用列表"      />      <ListView  android:id="@+id/listview"          android:layout_width="fill_parent"           android:layout_height="fill_parent"       />  </LinearLayout>  

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http://www.ophonesdn.com/article/show/80?