Android源码阅读－Filter过滤器

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);
}
}
}