29Android数据过滤机制

1.何谓Android的过滤机制？

Android对数据的处理是分层的，从上到下，可以分为：数据层、提供层、Cursor层、适配层、显示层。每个层次通过一定的机制，可以使数据发生变化时能够上下通知。如下：

显示层（ListView，GridView,AutoCompleteTextView等）

适配层（Adpater）

Cursor层（Cursor）

提供层（ContentProvider）

数据层（文件、sqlite、SharedPreference）

数据层是数据具体的存储方式，它可以包括文件、sqlite数据库以及SharedPreference。提供层向上层提供了统一的数据调用方式，并负责向其它应用共享数据。Cursor层将查询的数据统一成Cursor的形式来使用。适配层用来连接Cursor层和显示层，将数据和界面连接起来。显示层负责数据的显示。

另外，Andriod提供了数据的过滤机制，也就是在不改变数据存储的情况下，异步或同步的过滤符合条件的数据，并即时的显示在界面上。

比如：我的界面开始这样：



当我在搜索框中输入："C"的时候，开始过滤了：



2.Android做了哪些

1、为了实现数据的过滤，andorid设计了抽象类Filter，进行异步和同步的数据过滤操作。

2、在Adapter中继承Filterable，提供给使用者Filter，进行过滤。

3、在不同的View中，获得查询约束字符串，传递给Adapter，并且提供配合数据过滤的界面支持。

3.Filter类

Filter的使用流程如下：

调用filter方法 ->在另一线程中调用performFiltering进行数据查询->得到数据过滤结果后调用publishResults将结果返回到使用它的客户端。

该类中的performFiltering和publishResults均为抽象方法，需要继承者自己重写。

CursorFilter类就是Filter类的继承。CursorFilter在performFiltering中并没有直接进行数据的过滤，而是加入了CursorFilterClient成员，将过滤的操作转让给了CursorFilterClient,实际上CursorAdpater就是继承了CursorFilterClient接口，也就是说过滤操作实际上是在CursorAdapter中执行的。

4.Filterable接口

常用的Adapter基本上都继承了Filterable接口，如CursorAdapter，ArrayAdapter，SimpleAdapter等。该接口只有一个函数，名为getFilter，通过该函数可以通过Adaper获取Filter，然后通过该Filter进行过滤。

在CursorAdapter中，可以更改过滤的流程，有两种方式：

1、通过重写CursorAdapter的runQueryOnBackgroundThread函数，在函数中根据过滤约束字符串，重新查找生成新的Cursor。Adapter会适时将旧的Cursor进行替换。

2、通过调用setFilterQueryProvider函数，提供一个FilterQueryProvider，该对象含有runQuery方法，作用同runQueryOnBackgroundThread方法相同。

5.数据过滤功能的View的界面支持。

为了实现数据过滤的功能，在数据显示层，也有相应的支持。比如ListView和GridView，设置了setFilterText函数，通过该函数可以一方面进行数据的过滤，另一方面显示一个PopupWindow,提示用户输入了那种过滤条件。AutoCompleteTextView当用户在文本框输入文字时，自动进行过滤，并弹出列表显示过滤数据。

使用那种方法取决于您是不是重载CursorAdapter，以及您的过滤动作需要在Adpter中实现还是在主程序中实现。

6.实战
这部分会在会话界面的搜索框得到展示。稍后进行讲解。

//============================================================================================================================

API的说明：

　一、结构

　　　　public abstract class Filter extends Object

java.lang.Object

android.widget.Filter

　　二、概述

　　　　过滤器通过过滤模式来约束数据，通常由实现了Filterable接口的子类来生成。 过滤操作是通过调用 filter(CharSequence) 或者 filter(CharSequence,
android.widget.Filter.FilterListener)这些异步方法来完成的。以上方法一旦被调用，过滤请求就会被递交到请求队列中等待处理，同时该操作会取消那些之前递交的但是还没有被处理的请求。

　　三、构造函数

public Filter ()

　 创建一个新的异步过滤器。

　　四、公共方法

　　public CharSequence convertResultToString (Object resultValue)

　　 将受过滤的集合对象转换成CharSequence文本。所有继承了Filter的子类应该重写该方法。该方法的默认实现：如果参数为null则返回空字符串或者返回参数的字符串形式.

　　参数

resultValue 转换成CharSequence文本的对象

返回值

CharSequence 文本

　　public final void filter(CharSequence constraint, Filter.FilterListener listener)

　　启动一个异步的过滤操作。对该方法的调用会取消之前队列中等待处理的过滤请求并且递交新的过滤请求等待执行。完成过滤操作之后，通知监听器。

　　参数

　　constraint 过滤数据的约束条件

　　listener 监听过滤操作完成之后发出的通知

　　 参见

　　filter(CharSequence)

　　performFiltering(CharSequence)

　　publishResults(CharSequence, FilterResults results);

　　public final void filter(CharSequence constraint)

　　启动一个异步的过滤操作。对该方法的调用会取消之前队列中等待处理的过滤请求并且递交新的过滤请求等待执行。

　　参数

　　constraint 过滤数据的约束条件

参见
　　filter(CharSequence,
android.widget.Filter.FilterListener)



　　五、 受保护方法

　　protected abstract Filter.FilterResults performFiltering (CharSequence constraint)

根据约束条件调用一个工作线程过滤数据。子类必须实现该方法来执行过滤操作。过滤结果以Filter.FilterResults的形式返回，然后在UI线程中通过publishResults(CharSequence,android.widget.Filter.FilterResults)方法来发布。

　　约定：当约束条件为null时，原始数据必须被恢复。

　　参数

　　constraint 约束条件

　　返回值

　　过滤结果

　　参见

filter(CharSequence,
android.widget.Filter.FilterListener)

publishResults(CharSequence,
android.widget.Filter.FilterResults)

Filter.FilterResults

　　protected abstract void publishResults (CharSequence constraint, Filter.FilterResults results)

　　通过调用UI线程在用户界面发布过滤结果。子类必须实现该方法来显示performFiltering(CharSequence)的过滤结果。

　　参数

　　constraint 约束条件

　　results 过滤结果

　　参见

filter(CharSequence, android.widget.Filter.FilterListener)

　performFiltering(CharSequence)
　　　　　　　　Filter.FilterResults

源码：

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0  *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.widget;

import android.os.Handler;
import android.os.HandlerThread;
import android.os.Looper;
import android.os.Message;
import android.util.Log;

/**
 * <p>A filter constrains data with a filtering pattern.</p>
 *
 * <p>Filters are usually created by {@link android.widget.Filterable}
 * classes.</p>
 *
 * <p>Filtering operations performed by calling {@link #filter(CharSequence)} or
 * {@link #filter(CharSequence, android.widget.Filter.FilterListener)} are
 * performed asynchronously. When these methods are called, a filtering request
 * is posted in a request queue and processed later. Any call to one of these
 * methods will cancel any previous non-executed filtering request.</p>
 *
 * @see android.widget.Filterable
 */
public abstract class Filter {
    private static final String LOG_TAG = "Filter";
    
    private static final String THREAD_NAME = "Filter";
    private static final int FILTER_TOKEN = 0xD0D0F00D;
    private static final int FINISH_TOKEN = 0xDEADBEEF;

    private Handler mThreadHandler;
    private Handler mResultHandler;

    private Delayer mDelayer;

    private final Object mLock = new Object();

    /**
     * <p>Creates a new asynchronous filter.</p>
     */
    public Filter() {
        mResultHandler = new ResultsHandler();
    }

    /**
     * Provide an interface that decides how long to delay the message for a given query.  Useful
     * for heuristics such as posting a delay for the delete key to avoid doing any work while the
     * user holds down the delete key.
     *
     * @param delayer The delayer.
     * @hide
     */
    public void setDelayer(Delayer delayer) {
        synchronized (mLock) {
            mDelayer = delayer;
        }
    }

    /**
     * <p>Starts an asynchronous filtering operation. Calling this method
     * cancels all previous non-executed filtering requests and posts a new
     * filtering request that will be executed later.</p>
     *
     * @param constraint the constraint used to filter the data
     *
     * @see #filter(CharSequence, android.widget.Filter.FilterListener)
     */
    public final void filter(CharSequence constraint) {
        filter(constraint, null);
    }

    /**
     * <p>Starts an asynchronous filtering operation. Calling this method
     * cancels all previous non-executed filtering requests and posts a new
     * filtering request that will be executed later.</p>
     *
     * <p>Upon completion, the listener is notified.</p>
     *
     * @param constraint the constraint used to filter the data
     * @param listener a listener notified upon completion of the operation
     *
     * @see #filter(CharSequence)
     * @see #performFiltering(CharSequence)
     * @see #publishResults(CharSequence, android.widget.Filter.FilterResults)
     */
    public final void filter(CharSequence constraint, FilterListener listener) {
        synchronized (mLock) {
            if (mThreadHandler == null) {
                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);
            
            Message message = mThreadHandler.obtainMessage(FILTER_TOKEN);
    
            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;
    
            mThreadHandler.removeMessages(FILTER_TOKEN);
            mThreadHandler.removeMessages(FINISH_TOKEN);
            mThreadHandler.sendMessageDelayed(message, delay);
        }
    }

    /**
     * <p>Invoked in a worker thread to filter the data according to the
     * constraint. Subclasses must implement this method to perform the
     * filtering operation. Results computed by the filtering operation
     * must be returned as a {@link android.widget.Filter.FilterResults} that
     * will then be published in the UI thread through
     * {@link #publishResults(CharSequence,
     * android.widget.Filter.FilterResults)}.</p>
     *
     * <p><strong>Contract:</strong> When the constraint is null, the original
     * data must be restored.</p>
     *
     * @param constraint the constraint used to filter the data
     * @return the results of the filtering operation
     *
     * @see #filter(CharSequence, android.widget.Filter.FilterListener)
     * @see #publishResults(CharSequence, android.widget.Filter.FilterResults)
     * @see android.widget.Filter.FilterResults
     */
    protected abstract FilterResults performFiltering(CharSequence constraint);

    /**
     * <p>Invoked in the UI thread to publish the filtering results in the
     * user interface. Subclasses must implement this method to display the
     * results computed in {@link #performFiltering}.</p>
     *
     * @param constraint the constraint used to filter the data
     * @param results the results of the filtering operation
     *
     * @see #filter(CharSequence, android.widget.Filter.FilterListener)
     * @see #performFiltering(CharSequence)
     * @see android.widget.Filter.FilterResults
     */
    protected abstract void publishResults(CharSequence constraint,
            FilterResults results);

    /**
     * <p>Converts a value from the filtered set into a CharSequence. Subclasses
     * should override this method to convert their results. The default
     * implementation returns an empty String for null values or the default
     * String representation of the value.</p>
     *
     * @param resultValue the value to convert to a CharSequence
     * @return a CharSequence representing the value
     */
    public CharSequence convertResultToString(Object resultValue) {
        return resultValue == null ? "" : resultValue.toString();
    }

    /**
     * <p>Holds the results of a filtering operation. The results are the values
     * computed by the filtering operation and the number of these values.</p>
     */
    protected static class FilterResults {
        public FilterResults() {
            // nothing to see here
        }

        /**
         * <p>Contains all the values computed by the filtering operation.</p>
         */
        public Object values;

        /**
         * <p>Contains the number of values computed by the filtering
         * operation.</p>
         */
        public int count;
    }

    /**
     * <p>Listener used to receive a notification upon completion of a filtering
     * operation.</p>
     */
    public static interface FilterListener {
        /**
         * <p>Notifies the end of a filtering operation.</p>
         *
         * @param count the number of values computed by the filter
         */
        public void onFilterComplete(int count);
    }

    /**
     * <p>Worker thread handler. When a new filtering request is posted from
     * {@link android.widget.Filter#filter(CharSequence, android.widget.Filter.FilterListener)},
     * it is sent to this handler.</p>
     */
    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 {
                        args.results = performFiltering(args.constraint);
                    } catch (Exception e) {
                        args.results = new FilterResults();
                        Log.w(LOG_TAG, "An exception occured during performFiltering()!", e);
                    } finally {
                        message = mResultHandler.obtainMessage(what);
                        message.obj = args;
                        message.sendToTarget();
                    }

                    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;
            }
        }
    }

    /**
     * <p>Handles the results of a filtering operation. The results are
     * handled in the UI thread.</p>
     */
    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;

            publishResults(args.constraint, args.results);
            if (args.listener != null) {
                int count = args.results != null ? args.results.count : -1;
                args.listener.onFilterComplete(count);
            }
        }
    }

    /**
     * <p>Holds the arguments of a filtering request as well as the results
     * of the request.</p>
     */
    private static class RequestArguments {
        /**
         * <p>The constraint used to filter the data.</p>
         */
        CharSequence constraint;

        /**
         * <p>The listener to notify upon completion. Can be null.</p>
         */
        FilterListener listener;

        /**
         * <p>The results of the filtering operation.</p>
         */
        FilterResults results;
    }

    /**
     * @hide
     */
    public interface Delayer {

        /**
         * @param constraint The constraint passed to {@link Filter#filter(CharSequence)}
         * @return The delay that should be used for
         *         {@link Handler#sendMessageDelayed(android.os.Message, long)}
         */
        long getPostingDelay(CharSequence constraint);
    }
}

接口的源码：

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0  *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.widget;

/**
 * <p>Defines a filterable behavior. A filterable class can have its data
 * constrained by a filter. Filterable classes are usually
 * {@link android.widget.Adapter} implementations.</p>
 *
 * @see android.widget.Filter
 */
public interface Filterable {
    /**
     * <p>Returns a filter that can be used to constrain data with a filtering
     * pattern.</p>
     *
     * <p>This method is usually implemented by {@link android.widget.Adapter}
     * classes.</p>
     *
     * @return a filter used to constrain data
     */
    Filter getFilter();
}