Filter

顺便看看，Android中过滤器是怎么实现的？
注释中提到，Filter一般通过继承Filterable实现

具体实现

这是SimpleAdapter出现的一个过滤首字母item的一个过滤器

    private class SimpleFilter extends Filter {        @Override        protected FilterResults performFiltering(CharSequence prefix) {            FilterResults results = new FilterResults();            if (mUnfilteredData == null) {                mUnfilteredData = new ArrayList<Map<String, ?>>(mData);            }            if (prefix == null || prefix.length() == 0) {                ArrayList<Map<String, ?>> list = mUnfilteredData;                results.values = list;                results.count = list.size();            } else {                String prefixString = prefix.toString().toLowerCase();                ArrayList<Map<String, ?>> unfilteredValues = mUnfilteredData;                int count = unfilteredValues.size();                ArrayList<Map<String, ?>> newValues = new ArrayList<Map<String, ?>>(count);                for (int i = 0; i < count; i++) {                    Map<String, ?> h = unfilteredValues.get(i);                    if (h != null) {                        int len = mTo.length;                        for (int j = 0; j < len; j++) {                            String str = (String) h.get(mFrom[j]);                            String[] words = str.split(" ");                            int wordCount = words.length;                            for (int k = 0; k < wordCount; k++) {                                String word = words[k];                                if (word.toLowerCase().startsWith(prefixString)) {                                    newValues.add(h);                                    break;                                }                            }                        }                    }                }                results.values = newValues;                results.count = newValues.size();            }            return results;        }        @Override        protected void publishResults(CharSequence constraint, FilterResults results) {            //noinspection unchecked            mData = (List<Map<String, ?>>) results.values;            if (results.count > 0) {                notifyDataSetChanged();            } else {                notifyDataSetInvalidated();            }        }    }

通过performFiltering处理Result和publishResults返回数据进行刷新。

Filter抽象类源码

抽象类Filter中filter开启了对于数据的异步过滤操作。
寻找一下调用，发现AbsListView和AutoCompleteTextView 都有调用:
Abs中：

    // 判断类型    if (mAdapter instanceof Filterable) {                Filter f = ((Filterable) mAdapter).getFilter();                // Filter should not be null when we reach this part                if (f != null) {                    f.filter(s, this);                } else {                    throw new IllegalStateException("You cannot call onTextChanged with a non "                            + "filterable adapter");                }            }

Auto中:

    protected void performFiltering(CharSequence text, int keyCode) {        mFilter.filter(text, this);    }

filter的调用通过一个限制词和接口，接口判断完成百分比。

filter:

    public final void filter(CharSequence constraint, FilterListener listener) {        // 锁        synchronized (mLock) {            if (mThreadHandler == null) {            // 开一个线程进行 这个线程自带Looper                HandlerThread thread = new HandlerThread(                        THREAD_NAME, android.os.Process.THREAD_PRIORITY_BACKGROUND);                thread.start();                mThreadHandler = new RequestHandler(thread.getLooper());            }            final long delay = (mDelayer == null) ? 0 : mDelayer.getPostingDelay(constraint);            // 回收池拿一个msg            Message message = mThreadHandler.obtainMessage(FILTER_TOKEN);            // 包含了过滤的一切信息的对象            RequestArguments args = new RequestArguments();            // make sure we use an immutable copy of the constraint, so that            // it doesn't change while the filter operation is in progress                      args.constraint = constraint != null ? constraint.toString() : null;            args.listener = listener;            message.obj = args;                        // 移除了之前未处理的消息            mThreadHandler.removeMessages(FILTER_TOKEN);            mThreadHandler.removeMessages(FINISH_TOKEN);            mThreadHandler.sendMessageDelayed(message, delay);        }    }

处理request的handler：

     private class RequestHandler extends Handler {        public RequestHandler(Looper looper) {            super(looper);        }                /** * <p>Handles filtering requests by calling * {@link Filter#performFiltering} and then sending a message * with the results to the results handler.</p> * * @param msg the filtering request */ public void handleMessage(Message msg) { int what = msg.what; Message message; switch (what) { case FILTER_TOKEN: RequestArguments args = (RequestArguments) msg.obj; try { // 处理过程 args.results = performFiltering(args.constraint); } catch (Exception e) { args.results = new FilterResults(); Log.w(LOG_TAG, "An exception occured during performFiltering()!", e); } finally { // 返回值 message = mResultHandler.obtainMessage(what); message.obj = args; message.sendToTarget(); } // 结束调用 synchronized (mLock) { if (mThreadHandler != null) { Message finishMessage = mThreadHandler.obtainMessage(FINISH_TOKEN); mThreadHandler.sendMessageDelayed(finishMessage, 3000); } } break; case FINISH_TOKEN: synchronized (mLock) { if (mThreadHandler != null) { mThreadHandler.getLooper().quit(); mThreadHandler = null; } } break; } } }

处理结果的Handler：

    private class ResultsHandler extends Handler {        /** * <p>Messages received from the request handler are processed in the * UI thread. The processing involves calling * {@link Filter#publishResults(CharSequence, * android.widget.Filter.FilterResults)} * to post the results back in the UI and then notifying the listener, * if any.</p>  * * @param msg the filtering results */        @Override        public void handleMessage(Message msg) {            RequestArguments args = (RequestArguments) msg.obj;            // 返回数据            publishResults(args.constraint, args.results);            if (args.listener != null) {                int count = args.results != null ? args.results.count : -1;                args.listener.onFilterComplete(count);            }        }    }

Android源码阅读－Filter过滤器

Filter

具体实现

Filter抽象类源码

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