Android基础教程：CursorAdapter如何达成关键字过滤
发布时间：2021-11-24 19:34:11 所属栏目：教程 来源：互联网
导读：Android.widget.CursorAdapter 它首先实现了两个接口Filterable，CursorFilter.CursorFilterClient。 其中Filterable接口定义了getFilter()这个接口。 CursorFilterClient定义如下接口： CharSequence convertToString(Cursor cursor); Cursor runQueryOnBack
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Android.widget.CursorAdapter 它首先实现了两个接口Filterable，CursorFilter.CursorFilterClient。 其中Filterable接口定义了getFilter()这个接口。 CursorFilterClient定义如下接口： CharSequence convertToString(Cursor cursor); Cursor runQueryOnBackgroundThread(CharSequence constraint); Cursor getCursor(); void changeCursor(Cursor cursor); 注意：CursorFilter.CursorFilterClient是非public的，所以只有文档中看不到它，在源码中才能看到它。 CursorAdapter.java文件如下 package android.widget; -----------------------------------省略--------------------------------- public abstract class CursorAdapter extends BaseAdapter implements Filterable, CursorFilter.CursorFilterClient { /** * This field should be made private, so it is hidden from the SDK. * {@hide} */ protected boolean mDataValid; /** * This field should be made private, so it is hidden from the SDK. * {@hide} */ protected boolean mAutoRequery; /** * This field should be made private, so it is hidden from the SDK. * {@hide} */ protected Cursor mCursor; -----------------------------------省略--------------------------------- protected CursorFilter mCursorFilter; /** * This field should be made private, so it is hidden from the SDK. * {@hide} */ protected FilterQueryProvider mFilterQueryProvider; -----------------------------------省略--------------------------------- public Cursor getCursor() { return mCursor; } -----------------------------------省略--------------------------------- public void changeCursor(Cursor cursor) { -----------------------------------省略--------------------------------- } -----------------------------------省略--------------------------------- public CharSequence convertToString(Cursor cursor) { return cursor == null ? "" : cursor.toString(); } -----------------------------------省略--------------------------------- public Cursor runQueryOnBackgroundThread(CharSequence constraint) { if (mFilterQueryProvider != null) { return mFilterQueryProvider.runQuery(constraint); } return mCursor; } public Filter getFilter() { if (mCursorFilter == null) { mCursorFilter = new CursorFilter(this); } return mCursorFilter; } -----------------------------------省略--------------------------------- public FilterQueryProvider getFilterQueryProvider() { return mFilterQueryProvider; } -----------------------------------省略--------------------------------- public void setFilterQueryProvider(FilterQueryProvider filterQueryProvider) { mFilterQueryProvider = filterQueryProvider; } -----------------------------------省略--------------------------------- } CursorFilter文件如下： package android.widget; import android.database.Cursor; class CursorFilter extends Filter { CursorFilterClient mClient; interface CursorFilterClient { CharSequence convertToString(Cursor cursor); Cursor runQueryOnBackgroundThread(CharSequence constraint); Cursor getCursor(); void changeCursor(Cursor cursor); } CursorFilter(CursorFilterClient client) { mClient = client; } @Override public CharSequence convertResultToString(Object resultValue) { return mClient.convertToString((Cursor) resultValue); } @Override protected FilterResults performFiltering(CharSequence constraint) { Cursor cursor = mClient.runQueryOnBackgroundThread(constraint); FilterResults results = new FilterResults(); if (cursor != null) { results.count = cursor.getCount(); results.values = cursor; } else { results.count = 0; results.values = null; } return results; } @Override protected void publishResults(CharSequence constraint, FilterResults results) { Cursor oldCursor = mClient.getCursor(); if (results.values != null && results.values != oldCursor) { mClient.changeCursor((Cursor) results.values); } } } 关于Filter的更多内容参见《关键字过滤器Filter》。 如何使用Filter呢？ 调用CursorAdapter的getFilter方法得到一个Filter，调用它的filter (CharSequence constraint)方法。其中constraint就是关键字。 注意1:如果不给CursorAdapter设置FilterQueryProvider（通过setFilterQueryProvider方法）， 那么就需要重载Cursor runQueryOnBackgroundThread(CharSequence constraint)来实现对数据库的过滤查询。 当然FilterQueryProvider其实就是在它唯一的方法public abstract Cursor runQuery (CharSequence constraint)里面实现对数据库的过滤查询。 参考源代码可以知道如果提供了FilterQueryProvider，那么CursorAdapter就是在runQueryOnBackgroundThread方法中直接调用FilterQueryProvider的runQuery方法来进行数据库的过滤查询  （编辑：济南站长网） 【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容! |
