Android - SimpleCursorAdapter changeCursor 功能太慢

Question

我正在寻找一种解决方案来加快我的微调器的更新速度。目前我正在使用 SimpleCursorAdapter 并在我根据先前选择的微调器更改搜索条件时调用 ChangeCursor。

我做了一些计时测试，查询需要 5 毫秒到 60 毫秒，而 changeCursor 函数需要 600 毫秒到 4000 毫秒以上。是否有另一种方法可以更快地更新适配器上的光标？我没有使用相同的查询，所以我不能简单地重新查询游标然后调用 notifydatasetchanged。我必须创建一个新查询，然后取回一个新游标(也许有更好的方法来完成这部分)。

这是我目前的填充方式

private void writerSpinner() {
        String[] columns = new String[] { Passage.COL_WRITER_ID + " " + BaseColumns._ID, Passage.COL_WRITER_NAME };
        String whereClause = null;
        String groupBy = null;
        String orderBy = Passage.COL_WRITER_ID + " ASC";

        if (mAdapterPassage == null) {
            String[] columnsSpinner = new String[] { Passage.COL_WRITER_NAME };
            int[] to = new int[] { android.R.id.text1 };

            mAdapterPassage = new SimpleCursorAdapter(getActivity(), android.R.layout.simple_spinner_item, null, columnsSpinner, to);
            mAdapterPassage.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
            mPassage.setAdapter(mAdapterPassage);
            mPassage.setOnItemSelectedListener(onItemSelectedListener);
        }

        AsyncLoadData loadData = new AsyncLoadData(mAdapterPassage, mPassage, Passage.TABLE_NAME_WRITERS, columns, whereClause, groupBy, orderBy);
        loadData.execute();
    }

    private void updateChapterSpinner() {
        String[] columns = new String[] { Passage.COL_WRITER_ID + " " + BaseColumns._ID, Passage.COL_CHAPTER_ID };
        String whereClause = Passage.COL_WRITER_ID + " = " + mSelectedWriterId;
        String groupBy = Passage.COL_CHAPTER_ID;
        String orderBy = Passage.COL_CHAPTER_ID + " ASC";

        if (mAdapterChapter == null) {
            String[] columnsSpinner = new String[] { Passage.COL_CHAPTER_ID };
            int[] to = new int[] { android.R.id.text1 };

            mAdapterChapter = new SimpleCursorAdapter(getActivity(), android.R.layout.simple_spinner_item, null, columnsSpinner, to);
            mAdapterChapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
            mChapter.setAdapter(mAdapterChapter);
            mChapter.setOnItemSelectedListener(onItemSelectedListener);
        }

        AsyncLoadData loadData = new AsyncLoadData(mAdapterChapter, mChapter, Passage.TABLE_NAME_PASSAGES, columns, whereClause, groupBy, orderBy);
        loadData.execute();
    }

    private void updateVerseSpinner() {
        String[] columns = new String[] { Passage.COL_WRITER_ID + " " + BaseColumns._ID, Passage.COL_VERSE_ID };
        String whereClause = Passage.COL_WRITER_ID + " = " + mSelectedWriterId
                + " AND " + Passage.COL_CHAPTER_ID + " = " + mSelectedChapter;
        String groupBy = Passage.COL_VERSE_ID;
        String orderBy = Passage.COL_VERSE_ID + " ASC";


        if (mAdapterVerse == null) {
            String[] columnsSpinner = new String[] { Passage.COL_VERSE_ID };
            int[] to = new int[] { android.R.id.text1 };

            mAdapterVerse = new SimpleCursorAdapter(getActivity(), android.R.layout.simple_spinner_item, null, columnsSpinner, to);
            mAdapterVerse.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
            mVerse.setAdapter(mAdapterVerse);
            mVerse.setOnItemSelectedListener(onItemSelectedListener);
        }

        AsyncLoadData loadData = new AsyncLoadData(mAdapterVerse, mVerse, Passage.TABLE_NAME_PASSAGES, columns, whereClause, groupBy, orderBy);
        loadData.execute();
    }

private class AsyncLoadData extends AsyncTask<Void, Void, Void> {
        String mTableName; 
        String[] mColumns;
        String mWhereClause;
        String mGroupBy;
        String mOrderBy;
        Spinner mSpinner;
        Cursor mCursor;
        SimpleCursorAdapter mAdapter;

        public AsyncLoadData(SimpleCursorAdapter adapter, Spinner spinner, String tableName, String[] columns, String whereClause, String groupBy, String orderBy) {
            mAdapter = adapter;
            mSpinner = spinner;
            mTableName = tableName;
            mColumns = columns;
            mWhereClause = whereClause;
            mGroupBy = groupBy;
            mOrderBy = orderBy;
        }


        @Override
        protected void onPreExecute()
        {
            //mSpinner.setVisibility(View.GONE);
        }

        @Override
        protected Void doInBackground(Void... arg0) {
            long startCursor = new Date().getTime();
            mCursor = mDBHandler.query(mTableName, mColumns, mWhereClause, null, mGroupBy, null, mOrderBy);
            long timeToQuery = new Date().getTime() - startCursor;          

            Log.i("CursorQuery", "Time to Query Cursor " + mGroupBy + ": "  + timeToQuery + "ms");

            return null;
        }

        @Override
        protected void onPostExecute(Void result)
        {   
            long startAdapter = new Date().getTime();
            mAdapter.changeCursor(mCursor);
            long timeToChangeCursor = new Date().getTime() - startAdapter;

            Log.i("AdapterQuery", "Time to Change Cursor " + mGroupBy + ": " + timeToChangeCursor + "ms");

            mAdapter.notifyDataSetChanged();
            //mSpinner.setVisibility(View.VISIBLE);
        }
    }

private OnItemSelectedListener onItemSelectedListener = new OnItemSelectedListener() {

        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            switch(parent.getId()) {
            case R.id.bible_passage:
                mSelectedWriterId = position + 1;
                updateChapterSpinner();
                break;
            case R.id.bible_chapter:
                mSelectedChapter = position + 1;    
                updateVerseSpinner();
                break;
            case R.id.bible_verse:
                mSelectedVerse = position + 1;
                break;
            }
        }

        public void onNothingSelected(AdapterView<?> parent) {

        }
    };

Answer 1

问题

changeCursor 花费这么长时间的原因是返回的游标Database.query(...) 只在必要时初始化(所以它是游标的错误，而不是适配器的错误)。

游标初始化缓慢的原因是它解析一次整个结果集(因为它需要知道总数)。尽管 SQLite 非常快地返回大量查询，但 java 非常慢解析它们(比 SQLite 慢 100 到 1000 倍)。

解决方案

进来，HugeSQLiteCursor (with JavaDoc!)。我写了这个游标来解决这个问题。它加载结果递增地和自动地，而不是一次全部(用一个聪明的找出开销几乎为 0 的总计数的解决方法)。

Download the .jar file ,将它添加到您的 libs/ 文件夹，然后执行以下操作使用它(完全限定名称是 com.malabarba.hugesqlitecursor.HugeSQLiteCursor):

adapter.changeCursor(new HugeSQLiteCursor(db, stepSize,
                                          table, columnFields,
                                          selection, selectionArgs));

如您所见，由于结果是延迟加载的，因此您需要将数据库和查询参数传递给构造函数。创建后，游标应该在任何情况下都能完美运行以前使用 SQLiteCursor。

第二个参数(stepSize)，是你想要的项目数在创建游标时初始加载。 这很重要参数。

整个游标的初始化时间实际上是就好像它只有 stepSize 结果一样。但是不要让 stepSize 小于一个屏幕中的结果数。

这个 Cursor 有效地消除了“Java 太慢”的瓶颈。在我的 Nexus 4 上，它在不到 60 毫秒 的时间内返回 50.000 个结果的查询，而 SQLiteCursor 则需要大约 1000 毫秒。当然，如果您的查询非常庞大，以至于 SQLite 返回结果的速度也很慢，那么此游标只能帮助您到此为止。