android - 如何通知更新数据库的游标适配器

Question

我的 gridview Activity 当前的方式是在我的 onCreate 方法上，我启动了一个异步任务，该任务搜索我手机上的所有视频，然后使用 do while 循环将 id 和文件路径存储在 SQLite 数据库中。然后我调用一个游标适配器，它使用后台线程使用文件路径创建缩略图并将它们显示在 gridview 中。但是，我遇到了一个问题，即当我第一次启动 Activity 时，gridview 中没有显示任何内容。但是，当我再次打开它时，一切都会显示出来。所以我的问题是，当 Activity 第一次启动时，光标中没有任何内容，因此无法显示任何内容。

我的问题是，在后台线程中输入新数据时，我将如何更新游标适配器？我怎样才能触发游标适配器使用刚刚在后台线程中输入的数据？我的代码贴在下面(抱歉有点草率)。

创建时

public void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.preview);
GridView gridview = (GridView) this.findViewById(R.id.gridview);

cursor = getContentResolver().query(MediaStore.Video.Media.EXTERNAL_CONTENT_URI, mediaColumns, null, null, null);
columnindexid = cursor.getColumnIndexOrThrow(MediaStore.Video.Media._ID);
columnindexdata = cursor.getColumnIndexOrThrow(MediaStore.Video.Media.DATA);

entry = new GridviewData(this);
entry.open();

DataEntry putitin = new DataEntry(entry);
putitin.execute();

//the cursor used in the cursor adapter
Cursor curs = entry.adapterCursor();
videoidindex = entry.Indexfinder(curs);
videopathindex = entry.Indexfinder2(curs);

config = new ImageLoaderConfiguration.Builder(this)
.imageDownloader(new BaseImageDownloader(this))
.build();

ImageLoader.getInstance().init(config);
Log.i(TAG, "Before set adapter");
gridview.setAdapter(new VideoAdapter(this, curs, flags));
 }

将数据放入数据库的异步任务

private class DataEntry extends AsyncTask<Void, Integer, GridviewData>{
Cursor cursor;
GridviewData dataentry;
DataEntry(GridviewData gridviewdata){
    this.dataentry = gridviewdata;
    this.cursor = getContentResolver().query(MediaStore.Video.Media.EXTERNAL_CONTENT_URI,
            mediaColumns, null, null, null);

         columnindexid = cursor.getColumnIndexOrThrow(MediaStore.Video.Media._ID);
         columnindexdata = cursor.getColumnIndexOrThrow(MediaStore.Video.Media.DATA);
}

@Override
protected GridviewData doInBackground(Void... params) {

    cursor.moveToFirst();
    do {

        String videoid = cursor.getString(columnindexid);
        String videopath = cursor.getString(columnindexdata);

        int result = dataentry.findVideoID(videoid);
        if (result == 1){

            //this is where data is put into the database
            dataentry.addVideoinfo(videoid, videopath);

        }

        if (result == 0){
            Log.i(TAG, "Cursor wasn't processed, no getcount");
        }
        if(result == 2){
            Log.i(TAG, "The data is already there");
        }

    } while (cursor.moveToNext());
    Log.i(TAG, "After dowhile loop");
    cursor.close();

    return dataentry;   
}   
    }

光标适配器

class VideoAdapter extends CursorAdapter {
Context context; 
public VideoAdapter(Context context, Cursor c, int flags) {
    super(context, c, flags);
    this.context = context;
    }

@Override
public void bindView(View view, Context context, Cursor cursor) {
    ViewHolder holder = (ViewHolder) view.getTag();
    String fileid = cursor.getString(videoidindex);
    String filepath = cursor.getString(videopathindex);
    BitmapDownloader bitdl = new BitmapDownloader(fileid, filepath,    holder.imageview);
    bitdl.execute();
}

@Override
public View newView(Context context, Cursor cursor, ViewGroup parent) {
    LayoutInflater inflater = (LayoutInflater) context
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View eachgrid = inflater.inflate(R.layout.eachgrid, parent, false);
    ViewHolder holder = new ViewHolder();
    holder.imageview = (ImageView) eachgrid
            .findViewById(R.id.Imageview1);
    eachgrid.setTag(holder);
    return eachgrid;        
}

Answer 1

调用notifyDataSetChanged在你的后台线程完成后在你的适配器上。

Notifies the attached observers that the underlying data has been changed and any View reflecting the data set should refresh itself.