问题

Question

我希望找到一种解决方案来加快更新我的微调器。目前，每当我根据之前选择的微调器更改搜索条件时，我正在使用SimpleCursorAdapter并调用ChangeCursor。

我进行了一些时序测试，查询时间为5ms到60ms，而changeCursor函数需要600ms到4000ms +。是否有另一种更快速更新适配器上光标的方法？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。我必须创建一个新的查询，然后返回一个新的光标（也许有更好的方法来做这个部分）。

以下是我目前正在填充的方式

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(...)仅在必要时初始化（所以它是光标的故障，而不是适配器的故障。

光标初始化速度慢的原因是它解析了立即整个结果集（因为它需要知道总计数）。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!）。我写了这个光标来解决这个问题。它加载结果递增和自动，而不是一次全部（聪明的解决方法，找出总计数近乎0的开销。）

Download the .jar file，将其添加到您的libs/文件夹，并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));

正如您所看到的，因为结果是懒惰加载的，您需要将数据库和查询参数传递给构造函数。一旦创建，光标应该在任何情况下完美地工作之前使用的是SQLiteCursor。

第二个参数（stepSize）是您想要的项目数最初在创建光标时加载。 这很重要参数即可。

整个游标的初始化时间将是有效的就好像它只有stepSize个结果一样。但是不要让stepSize小于适合一个屏幕的结果数。

这个Cursor有效地消除了“Java太慢”的瓶颈。在我的Nexus 4上，它返回50.000结果的查询，小于 60ms ，而SQLiteCursor花费了大约1000ms。当然，如果你的查询非常庞大，即使SQLite返回结果的速度也很慢，那么这个游标只会让你到目前为止。

Android - SimpleCursorAdapter changeCursor函数太慢了

1 个答案:

问题

解决方案