Question

我正在将一个sqlite数据库读入tableLayout。我不想在一个单独的线程中执行此操作，而不是在没有ui更新的情况下等待很长时间。所以我使用AsyncTask来完成一些工作并发布结果。但是，我列表中只有大约1/4的项目实际上是在TableLayout上。没有AsyncTask它工作正常。列表中的大多数项都会抛出一个错误（我抓到了）java.util.concurrent.RejectedExecutionException。我不确定为什么会这样。这是我的代码。

myDB.execSQL("CREATE TABLE IF NOT EXISTS "
                + TableName
                + " (_id INTEGER PRIMARY KEY, filepath TEXT UNIQUE, title TEXT, artist TEXT, album TEXT, time TEXT, playcount NUMERIC);");

        Cursor c = myDB.rawQuery("SELECT * FROM " + TableName, null);         

        c.moveToFirst();
        if (c != null) {
            int color = 0xFFdfe8ea;
            this.startManagingCursor(c);
            // Loop through all Results
            do {
                try{
                    MyAsyncTask aTask = new MyAsyncTask();
                    String[]strings= {c.getString(c.getColumnIndex("title")),c.getString(c.getColumnIndex("artist")),c.getString(c.getColumnIndex("time")),c.getString(c.getColumnIndex("album")),""+color};
                    aTask.execute(strings);
                }catch(Exception e){
                    Log.w("****", e);
                }
        if (color == 0xFFdfe8ea) {
                    color = 0xFFf2f8fa;
                } else {
                    color = 0xFFdfe8ea;
                }
            } while (c.moveToNext());
        }

    } catch (SQLException e) {
        Log.e("****", e.toString());
    } finally {
        if (myDB != null) {
            myDB.close();
        }
    }

这里是AsyncTask

class MyAsyncTask extends AsyncTask<String, Void, View> {
    @Override
    protected View doInBackground(String... params) {
        int color = Integer.parseInt(params[4]);

        TableRow tr = new TableRow(MainActivity.this);
        tr.setLayoutParams(new LayoutParams(
                LayoutParams.FILL_PARENT,
                LayoutParams.WRAP_CONTENT));

        TextView space = new TextView(MainActivity.this);
        space.setText("");
        space.setBackgroundColor(color); //0xFFf2f8fa alternating
        space.setSingleLine();
        space.setPadding(2, 2, 2, 2);
        space.setGravity(Gravity.LEFT);
        space.setTextColor(0xFF000000);
        space.setLayoutParams(new LayoutParams(
                findViewById(R.id.spaceColumn).getWidth(),
                LayoutParams.WRAP_CONTENT));

        /* Create a Button to be the row-content. */
        TextView title = new TextView(MainActivity.this);
        title.setText(params[0]);
        title.setBackgroundColor(color); //0xFFf2f8fa alternating
        title.setSingleLine();
        title.setPadding(2, 2, 2, 2);
        title.setGravity(Gravity.LEFT);
        title.setTextColor(0xFF000000);
        title.setEllipsize(TruncateAt.END);
        title.setLayoutParams(new LayoutParams(
                0,
                LayoutParams.WRAP_CONTENT, 1));

        /* Create a Button to be the row-content. */
        TextView artist = new TextView(MainActivity.this);
        artist.setText(params[1]);
        artist.setBackgroundColor(color); //0xFFf2f8fa alternating
        artist.setSingleLine();
        artist.setPadding(2, 2, 2, 2);
        artist.setGravity(Gravity.LEFT);
        artist.setTextColor(0xFF000000);
        artist.setEllipsize(TruncateAt.END);
        artist.setLayoutParams(new LayoutParams(
                0,
                LayoutParams.WRAP_CONTENT, 1));

        /* Create a Button to be the row-content. */
        TextView time = new TextView(MainActivity.this);
        time.setText(params[2]);
        time.setBackgroundColor(color); //0xFFf2f8fa alternating
        time.setSingleLine();
        time.setPadding(2, 2, 2, 2);
        time.setGravity(Gravity.LEFT);
        time.setTextColor(0xFF000000);
        time.setLayoutParams(new LayoutParams(
                findViewById(R.id.timeColumn).getWidth(),
                LayoutParams.WRAP_CONTENT));

        /* Create a Button to be the row-content. */
        TextView album = new TextView(MainActivity.this);
        album.setText(params[3]);
        album.setBackgroundColor(color); //0xFFf2f8fa alternating
        album.setSingleLine();
        album.setPadding(2, 2, 2, 2);
        album.setGravity(Gravity.LEFT);
        album.setTextColor(0xFF000000);
        album.setEllipsize(TruncateAt.END);
        album.setLayoutParams(new LayoutParams(
                0,
                LayoutParams.WRAP_CONTENT, 1));

        /* Add Button to row. */
        tr.addView(space);
        tr.addView(title);
        tr.addView(artist);
        tr.addView(time);
        tr.addView(album);

        /* Add row to TableLayout. */
        return tr;
    }

    @Override
    protected void onPostExecute(View tr) {
        ((TableLayout) findViewById(R.id.tableLayout)).addView(tr, new TableLayout.LayoutParams(
                        LayoutParams.FILL_PARENT,
                        LayoutParams.WRAP_CONTENT));
    }

    @Override
    protected void onPreExecute() {
    }
 }

作为参考，这就是我修复它的方法。

class MyAsyncTask extends AsyncTask<Void, Song, Void> {

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

        SQLiteDatabase myDB = openOrCreateDatabase("DatabaseName", MODE_PRIVATE, null);
        String TableName = "songs";

        myDB.execSQL("CREATE TABLE IF NOT EXISTS "
                + TableName
                + " (_id INTEGER PRIMARY KEY, filepath TEXT UNIQUE, title TEXT, artist TEXT, album TEXT, time TEXT, playcount NUMERIC);");

        Cursor c = myDB.rawQuery("SELECT * FROM " + TableName, null);

        c.moveToFirst();
        int filepathIndex=c.getColumnIndex("filepath");
        int titleIndex=c.getColumnIndex("title");
        int artistIndex=c.getColumnIndex("artist");
        int albumIndex=c.getColumnIndex("album");
        int timeIndex=c.getColumnIndex("time");
        int playcountIndex=c.getColumnIndex("playcount");

        if (c != null) {
            int color = 0xFFdfe8ea;
         //   this.startManagingCursor(c);
            // Loop through all Results
            do {
                Song song = new Song(c.getString(filepathIndex),c.getString(titleIndex),c.getString(artistIndex),c.getString(albumIndex),c.getString(timeIndex),c.getInt(playcountIndex),color);
                // Add to song the data from your cursor
                publishProgress(song);

                if (color == 0xFFdfe8ea) {
                    color = 0xFFf2f8fa;
                } else {
                    color = 0xFFdfe8ea;
                }
            } while (c.moveToNext());
        }

        return null;
    }

    @Override
    protected void onPostExecute(Void item) {
    }

    @Override
    protected void onPreExecute() {
    }

    @Override
    protected void onProgressUpdate(Song... items) {
        for (Song song : items) {
            TableRow tr = new TableRow(MainActivity.this);
            tr.setLayoutParams(new LayoutParams(
                    LayoutParams.FILL_PARENT,
                    LayoutParams.WRAP_CONTENT));

            TextView space = new TextView(MainActivity.this);
            space.setText("");
            space.setBackgroundColor(song.color); //0xFFf2f8fa alternating
            space.setSingleLine();
            space.setPadding(2, 2, 2, 2);
            space.setGravity(Gravity.LEFT);
            space.setTextColor(0xFF000000);
            space.setLayoutParams(new LayoutParams(
                    findViewById(R.id.spaceColumn).getWidth(),
                    LayoutParams.WRAP_CONTENT));

            /* Create a Button to be the row-content. */
            TextView title = new TextView(MainActivity.this);
            title.setText(song.title);
            title.setBackgroundColor(song.color); //0xFFf2f8fa alternating
            title.setSingleLine();
            title.setPadding(2, 2, 2, 2);
            title.setGravity(Gravity.LEFT);
            title.setTextColor(0xFF000000);
            title.setEllipsize(TruncateAt.END);
            title.setLayoutParams(new LayoutParams(
                    0,
                    LayoutParams.WRAP_CONTENT, 1));

            /* Create a Button to be the row-content. */
            TextView artist = new TextView(MainActivity.this);
            artist.setText(song.artist);
            artist.setBackgroundColor(song.color); //0xFFf2f8fa alternating
            artist.setSingleLine();
            artist.setPadding(2, 2, 2, 2);
            artist.setGravity(Gravity.LEFT);
            artist.setTextColor(0xFF000000);
            artist.setEllipsize(TruncateAt.END);
            artist.setLayoutParams(new LayoutParams(
                    0,
                    LayoutParams.WRAP_CONTENT, 1));

            /* Create a Button to be the row-content. */
            TextView time = new TextView(MainActivity.this);
            time.setText(song.time);
            time.setBackgroundColor(song.color); //0xFFf2f8fa alternating
            time.setSingleLine();
            time.setPadding(2, 2, 2, 2);
            time.setGravity(Gravity.LEFT);
            time.setTextColor(0xFF000000);
            time.setLayoutParams(new LayoutParams(
                    findViewById(R.id.timeColumn).getWidth(),
                    LayoutParams.WRAP_CONTENT));

            /* Create a Button to be the row-content. */
            TextView album = new TextView(MainActivity.this);
            album.setText(song.album);
            album.setBackgroundColor(song.color); //0xFFf2f8fa alternating
            album.setSingleLine();
            album.setPadding(2, 2, 2, 2);
            album.setGravity(Gravity.LEFT);
            album.setTextColor(0xFF000000);
            album.setEllipsize(TruncateAt.END);
            album.setLayoutParams(new LayoutParams(
                    0,
                    LayoutParams.WRAP_CONTENT, 1));

            /* Add Button to row. */
            tr.addView(space);
            tr.addView(title);
            tr.addView(artist);
            tr.addView(time);
            tr.addView(album);

            // Add the row to the table
            ((TableLayout) findViewById(R.id.tableLayout)).addView(tr, new TableLayout.LayoutParams(
                    LayoutParams.FILL_PARENT,
                    LayoutParams.WRAP_CONTENT));
        }
    }
}

Answer 1

您看到此RejectedExceutionException的原因几乎可以肯定是因为您提交的请求过多。

我刚进入AsyncTask的代码，我注意到了：

private static final int CORE_POOL_SIZE = 5;
private static final int MAXIMUM_POOL_SIZE = 128;
private static final int KEEP_ALIVE = 1;

private static final BlockingQueue<Runnable> sPoolWorkQueue =
      new LinkedBlockingQueue<Runnable>(10);

/**
* An {@link Executor} that can be used to execute tasks in parallel.
*/
    public static final Executor THREAD_POOL_EXECUTOR
            = new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE,
                    TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory);

这将构建一个有界的LinkedBlockingQueue。绑定最多10个元素。该 MAXIMUM_POOL_SIZE我看到是128（这意味着如果需要，Executor最多会创建128个线程）。

一旦超过128个线程并提交到队列深度为10的新MyTask实例，您将获得RejectedExecutionException。当您使所有可用线程饱和并且队列中没有空间时，抛出此异常。

您可以通过在RejectedExecution发生时获取线程转储来轻松确认。

基本上，您可以在任何特定时间提交138个MyTask，但是一旦您同时提交了139个MyTask（不在应用程序的生命周期内），您将遇到此问题

编辑我更详细地了解了代码，并且最新版本（实际上自2011年1月16日起）应该永远不会发生此错误。

如果版本较旧，则会遇到此issue。

简而言之，如果你升级版本，这个问题就会消失，但是每个任务都会连续执行而不是同时执行。

Answer 2

如果您想使用AsyncTask执行此操作，请考虑使用publishProgress()，这样每个项目都会在从数据库中获取时添加。这样：

注意：请注意Song是一个包含name，album，artist和time属性的类。

class MyAsyncTask extends AsyncTask<Void, Song, Void> {
    @Override
    protected Void doInBackground(Void... params) {
        myDB.execSQL("CREATE TABLE IF NOT EXISTS "
            + TableName
            + " (_id INTEGER PRIMARY KEY, filepath TEXT UNIQUE, title TEXT, artist TEXT, album TEXT, time TEXT, playcount NUMERIC);");

        Cursor c = myDB.rawQuery("SELECT * FROM " + TableName, null);         

        c.moveToFirst();
        if (c != null) {
            int color = 0xFFdfe8ea;
            this.startManagingCursor(c);
            // Loop through all Results
            do {
                Song song = new Song();
                // Add to song the data from your cursor
                publishProgress(song);
            } while (c.moveToNext());
        }

        return null;
    }

    @Override
    protected void onPostExecute(Void item) {
    }

    @Override
    protected void onPreExecute() {
    }       

    @Override
    protected void onProgressUpdate(Song... items) {
        for (Song song : items) {    
            TableRow tr = new TableRow(MainActivity.this);
            tr.setLayoutParams(new LayoutParams(
                    LayoutParams.FILL_PARENT,
                    LayoutParams.WRAP_CONTENT));

            TextView space = new TextView(MainActivity.this);
            space.setText("");
            space.setBackgroundColor(color); //0xFFf2f8fa alternating
            space.setSingleLine();
            space.setPadding(2, 2, 2, 2);
            space.setGravity(Gravity.LEFT);
            space.setTextColor(0xFF000000);
            space.setLayoutParams(new LayoutParams(
                    findViewById(R.id.spaceColumn).getWidth(),
                    LayoutParams.WRAP_CONTENT));

            /* Create a Button to be the row-content. */
            TextView title = new TextView(MainActivity.this);
            title.setText(song.getTitle());
            title.setBackgroundColor(color); //0xFFf2f8fa alternating
            title.setSingleLine();
            title.setPadding(2, 2, 2, 2);
            title.setGravity(Gravity.LEFT);
            title.setTextColor(0xFF000000);
            title.setEllipsize(TruncateAt.END);
            title.setLayoutParams(new LayoutParams(
                    0,
                    LayoutParams.WRAP_CONTENT, 1));

            /* Create a Button to be the row-content. */
            TextView artist = new TextView(MainActivity.this);
            artist.setText(song.getArtist());
            artist.setBackgroundColor(color); //0xFFf2f8fa alternating
            artist.setSingleLine();
            artist.setPadding(2, 2, 2, 2);
            artist.setGravity(Gravity.LEFT);
            artist.setTextColor(0xFF000000);
            artist.setEllipsize(TruncateAt.END);
            artist.setLayoutParams(new LayoutParams(
                    0,
                    LayoutParams.WRAP_CONTENT, 1));

            /* Create a Button to be the row-content. */
            TextView time = new TextView(MainActivity.this);
            time.setText(song.getTime());
            time.setBackgroundColor(color); //0xFFf2f8fa alternating
            time.setSingleLine();
            time.setPadding(2, 2, 2, 2);
            time.setGravity(Gravity.LEFT);
            time.setTextColor(0xFF000000);
            time.setLayoutParams(new LayoutParams(
                    findViewById(R.id.timeColumn).getWidth(),
                    LayoutParams.WRAP_CONTENT));

            /* Create a Button to be the row-content. */
            TextView album = new TextView(MainActivity.this);
            album.setText(song.getAlbum());
            album.setBackgroundColor(color); //0xFFf2f8fa alternating
            album.setSingleLine();
            album.setPadding(2, 2, 2, 2);
            album.setGravity(Gravity.LEFT);
            album.setTextColor(0xFF000000);
            album.setEllipsize(TruncateAt.END);
            album.setLayoutParams(new LayoutParams(
                    0,
                    LayoutParams.WRAP_CONTENT, 1));

            /* Add Button to row. */
            tr.addView(space);
            tr.addView(title);
            tr.addView(artist);
            tr.addView(time);
            tr.addView(album);

            // Add the row to the table
            ((TableLayout) findViewById(R.id.tableLayout)).addView(tr, new TableLayout.LayoutParams(
                            LayoutParams.FILL_PARENT,
                            LayoutParams.WRAP_CONTENT));
        }
    }
 }

我相信你错误地理解了AsyncTask背后的概念，我强烈建议你重读its documentation at Android Developers，因为它的概念有点难以理解，但是当你这么做时非常强大。正如Romain Guy对您的回答发表评论，您只能在onPreExecute（），onProgressUpdate（）和onPostExecute（）方法上执行UI代码。

Answer 3

我认为你不需要为此创建一个AsyncTask。您无法从网络中获取任何内容或下载图像。它只是标准装载。

我会使用'limit'限制SQL中的结果。

另外，你是在适配器内做的吗？因为我认为您要将所有内容添加到列表中，您应该在布局中创建列表视图并设置适配器。也许扩展BaseAdapter。

每个适配器都有一个名为getView的方便方法，只有在它可见时才会被调用，并且应该有助于解决问题。

这是适配器的示例：

public class MyAdapter extends BaseAdapter {

    private Context context = null;
    private Cursor cursor;

    public MyAdapter(Context context){

        this.context = context;     
        SQLiteDatabase db = DatabaseHelper.getInstance(context).getReadableDatabase();              
        this.cursor = db.query("YOUR QUERY");

    }

    @Override
    public int getCount() {
        return this.cursor.getCount();
    }


    public Cursor getCursor() {
        return cursor;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        LinearLayout row;

        try {           
        cursor.moveToPosition(position);

        if (convertView == null) {      
            row = (LinearLayout) LayoutInflater.from(context).inflate(R.layout.myRowLayout, parent, false);
            } else {
            row = (LinearLayout) convertView;
            }

        TextView name = (TextView) row.findViewById(R.id.myLayoutId);
        name.setText(cursor.getString(cursor.getColumnIndex("your column")));

        } catch (Exception e) {
            row = null;
            Log.e(LOG_TAG, "" + e.getMessage());
            e.printStackTrace();
        }

        return row;

    }

    @Override
    public MoneyCurrency getItem(int position) {        
        this.cursor.moveToPosition(position);
        long id = this.cursor.getLong(this.cursor.getColumnIndex("your column id")); 
        return new Object.read(id, context, null); //Return whatever you want to show in that row. This is used if you want to use onClick listeners or menus
    }

    @Override
    public long getItemId(int position) {
        this.cursor.moveToPosition(position);
        return this.cursor.getLong(this.cursor.getColumnIndex("your id column"));
    }



    }

从android上的asyncTask获取java.util.concurrent.RejectedExecutionException

3 个答案: