学步园

from:  http://www.cnblogs.com/rxwen/archive/2009/11/30/1713031.html

In this post, I'll show some basic operations in android with a simple video player. The demo shows how to:

Use explicit intent

List video files with ListView

, ContentProvider & MediaProvider

Retrieve data from another Activity with startActivityForResult


Play video file with VideoView

Basically,
the demo is composed of two activities. The first activity (Main) is a
video player with a button on it. When you click the button, the second
activity(VideoSelector) shows and lists video files available on the
device. Then, after you pick a video from the list, you return to Main
activiry and it starts playing the video you selected.

1. Use explicit intent

On
android, an intent can be implicit or explicit. An explicit intent
clearly designates the component to start. Because explicit intent uses
the name of target component, it's usually used inside an application.
On contrast, implicit intent specifies desired action, and let the
system to pick the best match component.
In our demo, we want to use
the VideoSelector to select a video file, rather than the system
built-in media selector, so we use explicit intent to start activity.
To create explicit intent, we just need to pass the designated
component class name to intent, as shown below.

               Intent i = new Intent();


               i.setClass(v.getContext(), VideoSelector.class);


               startActivityForResult(i, 0);

The use of startActivityForResult will be explained later.

2. List video files

Android
provides a ListActivity class to list data provided by a
ContentProvider. We can take advantage of it to list video files
available on current device rather than start from scratch. To use it,
we simply make it the base class for our activity, meanwhile, add a
ListView with id "@android:id/list" in the activity's layout. And the
final thing we need to do is set the datasource for the list with
setListAdapter method.
Android also provides a MediaProvider that can list all video files. It's the default provider when we use ContentResolver
to query MediaStore.Video.Media.

   @Override


   protected void onListItemClick(ListView l, View v, int position, long id)


   { // in VideoSelector.java


       String filePath = mCursor.getString(mCursor.getColumnIndex(MediaStore.Video.Media.DATA));


         mCursor.moveToPosition(position);


       Intent result = new Intent();


       result.putExtra(FILE_PATH, filePath);


       setResult(RESULT_OK, result);


       finish();


   }




   @Override


     protected void onActivityResult(int requestCode, int resultCode, Intent data) {


       // in Main.java


       super.onActivityResult(requestCode, resultCode, data);


       if (RESULT_OK == resultCode) {


             Bundle bd = data.getExtras();


           String path = bd.getString(VideoSelector.FILE_PATH);


           m_vvPlayer.setVideoPath(path);


           m_vvPlayer.start();


       }


   }