如您所知，android上的内置媒体扫描程序会定期扫描整个文件系统并生成媒体（照片+视频）预览缩略图。这些是Gallery应用程序显示的缩略图。
在我的应用中，我有一个旋转木马，我想在仅限视频中显示自动生成的缩略图。出于速度原因，因为它们已经存在。不幸的是，文档在如何实际获取它们方面非常缺乏。
public class MainActivity extends Activity {
private Cursor cursor;
private int columnIndex;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.content_main);
// Set up an array of the Thumbnail Image ID column we want
String[] projection = {MediaStore.Video.Thumbnails.VIDEO_ID};
// Create the cursor pointing to the SDCard
cursor = managedQuery( MediaStore.Video.Thumbnails.EXTERNAL_CONTENT_URI,
projection, // Which columns to return
null, // Return all rows
null,
null);
System.err.println("qqq video cnt=" + cursor.getCount());
// Get the column index of the Thumbnails Image ID
columnIndex = cursor.getColumnIndexOrThrow(projection[0]);
GridView sdcardImages = (GridView) findViewById(R.id.sdcard);
sdcardImages.setAdapter(new ImageAdapter(this));
// Set up a click listener
sdcardImages.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView parent, View v, int position, long id) {
// Get the data location of the image
String[] projection = {MediaStore.Video.Media.DATA};
cursor = managedQuery( MediaStore.Video.Media.EXTERNAL_CONTENT_URI,
projection, // Which columns to return
null, // Return all rows
null,
null);
columnIndex = cursor.getColumnIndexOrThrow(projection[0]);
cursor.moveToPosition(position);
// Get image filename
String imagePath = cursor.getString(columnIndex);
// Use this path to do further processing, i.e. full screen display
System.err.println("qqq path=" + imagePath);
}
});
}
private class ImageAdapter extends BaseAdapter {
private Context context;
public ImageAdapter(Context localContext) {
context = localContext;
}
public int getCount() {
System.err.println("qqq count " + cursor.getCount());
return cursor.getCount();
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
ImageView picturesView;
if (convertView == null) {
picturesView = new ImageView(context);
// Move cursor to current position
cursor.moveToPosition(position);
// Get the current value for the requested column
int imageID = cursor.getInt(columnIndex);
Uri uri = Uri.withAppendedPath(
MediaStore.Video.Thumbnails.EXTERNAL_CONTENT_URI, "" + imageID);
System.err.println("qqq getview uri="+uri.toString());
// Set the content of the image based on the provided URI
picturesView.setImageURI(uri);
picturesView.setScaleType(ImageView.ScaleType.FIT_CENTER);
picturesView.setPadding(8, 8, 8, 8);
picturesView.setLayoutParams(new GridView.LayoutParams(100, 100));
//picturesView.setImageBitmap(BitmapFactory.decodeResource(getResources(), android.R.drawable.ic_btn_speak_now));
}
else {
picturesView = (ImageView)convertView;
}
return picturesView;
}
}
}
我得到的日志如下。它确实显示了正确的视频数量（2），但即使缩略图媒体URL“看起来不错”，返回的Bitmap对象也是nil。有什么想法吗？
W/System.err: qqq video cnt=2
W/System.err: qqq count 2
W/System.err: qqq count 2
W/System.err: qqq count 2
W/System.err: qqq getview uri=content://media/external/video/thumbnails/2484
W/System.err: qqq getview uri=content://media/external/video/thumbnails/2483
W/System.err: qqq count 2
W/System.err: qqq getview uri=content://media/external/video/thumbnails/2484
W/System.err: qqq count 2
答案 0 :(得分：0)
以下是如何做到的。请注意，缩略图路径可以是null，如果视频已损坏或使用编解码器进行编码，则无法解析。
public class MainActivity extends Activity {
private Cursor cursor;
private int columnIndex;
ArrayList thumbs = new ArrayList();
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.content_main);
final String[] columns = {
BaseColumns._ID, MediaStore.MediaColumns.DATA
};
ContentResolver cr = this.getContentResolver();
Cursor cursor = cr.query(MediaStore.Video.Media.EXTERNAL_CONTENT_URI, columns, null, null, null);
boolean cancel = false;
if(null != cursor){
while(cursor.moveToNext() && !cancel){
String fileName = cursor.getString(cursor.getColumnIndex(MediaStore.MediaColumns.DATA));
int imageId = cursor.getInt(cursor.getColumnIndex(BaseColumns._ID));
thumbs.add(new Integer(imageId));
System.err.println("qqq " + fileName + " " + imageId);
}
}
GridView sdcardImages = (GridView) findViewById(R.id.sdcard);
sdcardImages.setAdapter(new ImageAdapter(this));
}
private class ImageAdapter extends BaseAdapter {
private Context context;
public ImageAdapter(Context localContext) {
context = localContext;
}
public int getCount() {
System.err.println("qqq count " + thumbs.size());//cursor.getCount());
//return cursor.getCount();
return thumbs.size();
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
ImageView picturesView;
if (convertView == null) {
picturesView = new ImageView(context);
picturesView.setScaleType(ImageView.ScaleType.FIT_CENTER);
picturesView.setPadding(8, 8, 8, 8);
picturesView.setLayoutParams(new GridView.LayoutParams(250, 250));
Bitmap myBitmap = BitmapFactory.decodeResource(getResources(), android.R.drawable.ic_menu_camera);
Integer t = (Integer)thumbs.get(position);
String path= getThumbPath(getContentResolver(), t.intValue());
if (path != null) {
System.err.println("qqq getting " + path);
File f = new File(path);
if (!f.exists()) {
System.err.println("qqq invalid file! " + path);
}
myBitmap = BitmapFactory.decodeFile(path);//imgFile.getAbsolutePath());
}
picturesView.setImageBitmap(myBitmap);
}
else {
picturesView = (ImageView)convertView;
}
return picturesView;
}
}
public String getThumbPath(ContentResolver contentResolver, long photoId) {
String path=null;
Cursor thumbnails = contentResolver.query(android.provider.MediaStore.Video.Thumbnails.EXTERNAL_CONTENT_URI,
null, android.provider.MediaStore.Video.Thumbnails.VIDEO_ID + "=?", new String[]{String.valueOf(photoId)}, null);
for (thumbnails.moveToFirst(); !thumbnails.isAfterLast(); thumbnails.moveToNext()) {
long thumbnailId = thumbnails.getLong(thumbnails.getColumnIndex(android.provider.MediaStore.Video.Thumbnails._ID));
path = thumbnails.getString(thumbnails.getColumnIndex(android.provider.MediaStore.Video.Thumbnails.DATA));
break;
}
thumbnails.close();
return path;
}
}