/**
 * Copyright (C) 2006 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.os;

import android.util.Log;
import android.util.Printer;
//引入这样一个类的作用
import java.lang.reflect.Modifier;

public class Handler {
    /**
     * Set this flag to true to detect anonymous, local or member classes
     * that extend this Handler class and that are not static. These kind
     * of classes can potentially create leaks.
     */
    private static final boolean FIND_POTENTIAL_LEAKS = false;
    private static final String TAG = "Handler";

    /***
     * 学习内部接口的使用方法及优势
     * Callback interface you can use when instantiating a Handler to avoid
     * having to implement your own subclass of Handler.
     */
    //定义一个处理消息的内部接口，马蛋，接口真多，何时调用，返回值也很重要
    public interface Callback {
        public boolean handleMessage(Message msg);
    }
    
    /***
     * Subclasses must implement this to receive messages.
     */
    //子类需要实现该方法以处理消息，我们的自由
    public void handleMessage(Message msg) {
    }
    
    //一般不会主动调用吧
    public void dispatchMessage(Message msg) {
        if (msg.callback != null) {
            handleCallback(msg);
        } else {
            //设置了callback时的处理方法
            if (mCallback != null) {
                //接口是否实现，该callback必须含有handlemessage方法，看返回值
                if (mCallback.handleMessage(msg)) {
                    return;
                }
            }
            //最后调用本身的handlemessage
            handleMessage(msg);
        }
    }

    /***
     * Default constructor associates this handler with the queue for the
     * current thread.
     *
     * If there isn't one, this handler won't be able to receive messages.
     */
    //默认构造函数，和当前线程的消息队列绑定，如果当前线程没有looper，则不能创建handler
    public Handler() {
        if (FIND_POTENTIAL_LEAKS) {
            //这用到了反射
            final Class<? extends Handler> klass = getClass();
            if ((klass.isAnonymousClass() || klass.isMemberClass() || klass.isLocalClass()) &&
                    (klass.getModifiers() & Modifier.STATIC) == 0) {
                //为什么会有这个提示，何时会出现
                Log.w(TAG, "The following Handler class should be static or leaks might occur: " +
                    klass.getCanonicalName());
            }
        }
        //获取当前looper
        mLooper = Looper.myLooper();
        if (mLooper == null) {
            //创建handler的前提是该线程拥有looper
            throw new RuntimeException(
                "Can't create handler inside thread that has not called Looper.prepare()");
        }
        //获取当前消息队列
        mQueue = mLooper.mQueue;
        mCallback = null;
    }

    /***
     * Constructor associates this handler with the queue for the
     * current thread and takes a callback interface in which you can handle
     * messages.
     */
    //加入回调
    public Handler(Callback callback) {
        if (FIND_POTENTIAL_LEAKS) {
            final Class<? extends Handler> klass = getClass();
            if ((klass.isAnonymousClass() || klass.isMemberClass() || klass.isLocalClass()) &&
                    (klass.getModifiers() & Modifier.STATIC) == 0) {
                Log.w(TAG, "The following Handler class should be static or leaks might occur: " +
                    klass.getCanonicalName());
            }
        }

        mLooper = Looper.myLooper();
        if (mLooper == null) {
            throw new RuntimeException(
                "Can't create handler inside thread that has not called Looper.prepare()");
        }
        mQueue = mLooper.mQueue;
        mCallback = callback;
    }

    /***
     * Use the provided queue instead of the default one.
     */
    //不使用默认的looper
    public Handler(Looper looper) {
        mLooper = looper;
        mQueue = looper.mQueue;
        mCallback = null;
    }

    /***
     * Use the provided queue instead of the default one and take a callback
     * interface in which to handle messages.
     */
    public Handler(Looper looper, Callback callback) {
        mLooper = looper;
        mQueue = looper.mQueue;
        mCallback = callback;
    }

    /***
     * Returns a string representing the name of the specified message.
     * The default implementation will either return the class name of the
     * message callback if any, or the hexadecimal representation of the
     * message "what" field.
     *  
     * @param message The message whose name is being queried 
     */
    //获取消息的名字,message.callback?
    public String getMessageName(Message message) {
        if (message.callback != null) {
            return message.callback.getClass().getName();
        }
        return "0x" + Integer.toHexString(message.what);
    }

    /***
     * Returns a new {@link android.os.Message Message} from the global message pool. More efficient than
     * creating and allocating new instances. The retrieved message has its handler set to this instance (Message.target == this).
     *  If you don't want that facility, just call Message.obtain() instead.
     */
    //直接调用message的方法，传入handler的意义
    public final Message obtainMessage()
    {
        return Message.obtain(this);
    }

    /***
     * Same as {@link #obtainMessage()}, except that it also sets the what member of the returned Message.
     * 
     * @param what Value to assign to the returned Message.what field.
     * @return A Message from the global message pool.
     */
    public final Message obtainMessage(int what)
    {
        return Message.obtain(this, what);
    }
    
    /***
     * 
     * Same as {@link #obtainMessage()}, except that it also sets the what and obj members 
     * of the returned Message.
     * 
     * @param what Value to assign to the returned Message.what field.
     * @param obj Value to assign to the returned Message.obj field.
     * @return A Message from the global message pool.
     */
    public final Message obtainMessage(int what, Object obj)
    {
        return Message.obtain(this, what, obj);
    }

    /***
     * 
     * Same as {@link #obtainMessage()}, except that it also sets the what, arg1 and arg2 members of the returned
     * Message.
     * @param what Value to assign to the returned Message.what field.
     * @param arg1 Value to assign to the returned Message.arg1 field.
     * @param arg2 Value to assign to the returned Message.arg2 field.
     * @return A Message from the global message pool.
     */
    public final Message obtainMessage(int what, int arg1, int arg2)
    {
        return Message.obtain(this, what, arg1, arg2);
    }
    
    /***
     * 
     * Same as {@link #obtainMessage()}, except that it also sets the what, obj, arg1,and arg2 values on the 
     * returned Message.
     * @param what Value to assign to the returned Message.what field.
     * @param arg1 Value to assign to the returned Message.arg1 field.
     * @param arg2 Value to assign to the returned Message.arg2 field.
     * @param obj Value to assign to the returned Message.obj field.
     * @return A Message from the global message pool.
     */
    public final Message obtainMessage(int what, int arg1, int arg2, Object obj)
    {
        return Message.obtain(this, what, arg1, arg2, obj);
    }

    /***
     * Causes the Runnable r to be added to the message queue.
     * The runnable will be run on the thread to which this handler is 
     * attached. 
     *  
     * @param r The Runnable that will be executed.
     * 
     * @return Returns true if the Runnable was successfully placed in to the 
     *         message queue.  Returns false on failure, usually because the
     *         looper processing the message queue is exiting.
     */
    //将runnable对象添加到消息队列
    public final boolean post(Runnable r)
    {
       return  sendMessageDelayed(getPostMessage(r), 0);
    }
    
    /***
     * Causes the Runnable r to be added to the message queue, to be run
     * at a specific time given by <var>uptimeMillis</var>.
     * <b>The time-base is {@link android.os.SystemClock#uptimeMillis}.</b>
     * The runnable will be run on the thread to which this handler is attached.
     *
     * @param r The Runnable that will be executed.
     * @param uptimeMillis The absolute time at which the callback should run,
     *         using the {@link android.os.SystemClock#uptimeMillis} time-base.
     *  
     * @return Returns true if the Runnable was successfully placed in to the 
     *         message queue.  Returns false on failure, usually because the
     *         looper processing the message queue is exiting.  Note that a
     *         result of true does not mean the Runnable will be processed -- if
     *         the looper is quit before the delivery time of the message
     *         occurs then the message will be dropped.
     */
    public final boolean postAtTime(Runnable r, long uptimeMillis)
    {
        return sendMessageAtTime(getPostMessage(r), uptimeMillis);
    }
    
    /***
     * Causes the Runnable r to be added to the message queue, to be run
     * at a specific time given by <var>uptimeMillis</var>.
     * <b>The time-base is {@link android.os.SystemClock#uptimeMillis}.</b>
     * The runnable will be run on the thread to which this handler is attached.
     *
     * @param r The Runnable that will be executed.
     * @param uptimeMillis The absolute time at which the callback should run,
     *         using the {@link android.os.SystemClock#uptimeMillis} time-base.
     * 
     * @return Returns true if the Runnable was successfully placed in to the 
     *         message queue.  Returns false on failure, usually because the
     *         looper processing the message queue is exiting.  Note that a
     *         result of true does not mean the Runnable will be processed -- if
     *         the looper is quit before the delivery time of the message
     *         occurs then the message will be dropped.
     *         
     * @see android.os.SystemClock#uptimeMillis
     */
    public final boolean postAtTime(Runnable r, Object token, long uptimeMillis)
    {
        return sendMessageAtTime(getPostMessage(r, token), uptimeMillis);
    }
    
    /***
     * Causes the Runnable r to be added to the message queue, to be run
     * after the specified amount of time elapses.
     * The runnable will be run on the thread to which this handler
     * is attached.
     *  
     * @param r The Runnable that will be executed.
     * @param delayMillis The delay (in milliseconds) until the Runnable
     *        will be executed.
     *        
     * @return Returns true if the Runnable was successfully placed in to the 
     *         message queue.  Returns false on failure, usually because the
     *         looper processing the message queue is exiting.  Note that a
     *         result of true does not mean the Runnable will be processed --
     *         if the looper is quit before the delivery time of the message
     *         occurs then the message will be dropped.
     */
    public final boolean postDelayed(Runnable r, long delayMillis)
    {
        return sendMessageDelayed(getPostMessage(r), delayMillis);
    }
    
    /***
     * Posts a message to an object that implements Runnable.
     * Causes the Runnable r to executed on the next iteration through the
     * message queue. The runnable will be run on the thread to which this
     * handler is attached.
     * <b>This method is only for use in very special circumstances -- it
     * can easily starve the message queue, cause ordering problems, or have
     * other unexpected side-effects.</b>
     *  
     * @param r The Runnable that will be executed.
     * 
     * @return Returns true if the message was successfully placed in to the 
     *         message queue.  Returns false on failure, usually because the
     *         looper processing the message queue is exiting.
     */
    public final boolean postAtFrontOfQueue(Runnable r)
    {
        return sendMessageAtFrontOfQueue(getPostMessage(r));
    }

    /***
     * Remove any pending posts of Runnable r that are in the message queue.
     */
    //直接从消息队列中移除
    public final void removeCallbacks(Runnable r)
    {
        mQueue.removeMessages(this, r, null);
    }

    /***
     * Remove any pending posts of Runnable <var>r</var> with Object
     * <var>token</var> that are in the message queue.  If <var>token</var> is null,
     * all callbacks will be removed.
     */
    public final void removeCallbacks(Runnable r, Object token)
    {
        mQueue.removeMessages(this, r, token);
    }

    /***
     * Pushes a message onto the end of the message queue after all pending messages
     * before the current time. It will be received in {@link #handleMessage},
     * in the thread attached to this handler.
     *  
     * @return Returns true if the message was successfully placed in to the 
     *         message queue.  Returns false on failure, usually because the
     *         looper processing the message queue is exiting.
     */
    //将一个消息推到消息队列的末端
    public final boolean sendMessage(Message msg)
    {
        return sendMessageDelayed(msg, 0);
    }

    /***
     * Sends a Message containing only the what value.
     *  
     * @return Returns true if the message was successfully placed in to the 
     *         message queue.  Returns false on failure, usually because the
     *         looper processing the message queue is exiting.
     */
    public final boolean sendEmptyMessage(int what)
    {
        return sendEmptyMessageDelayed(what, 0);
    }

    /***
     * Sends a Message containing only the what value, to be delivered
     * after the specified amount of time elapses.
     * @see #sendMessageDelayed(android.os.Message, long) 
     * 
     * @return Returns true if the message was successfully placed in to the 
     *         message queue.  Returns false on failure, usually because the
     *         looper processing the message queue is exiting.
     */
    public final boolean sendEmptyMessageDelayed(int what, long delayMillis) {
        Message msg = Message.obtain();
        msg.what = what;
        return sendMessageDelayed(msg, delayMillis);
    }

    /***
     * Sends a Message containing only the what value, to be delivered 
     * at a specific time.
     * @see #sendMessageAtTime(android.os.Message, long)
     *  
     * @return Returns true if the message was successfully placed in to the 
     *         message queue.  Returns false on failure, usually because the
     *         looper processing the message queue is exiting.
     */

    public final boolean sendEmptyMessageAtTime(int what, long uptimeMillis) {
        Message msg = Message.obtain();
        msg.what = what;
        return sendMessageAtTime(msg, uptimeMillis);
    }

    /***
     * Enqueue a message into the message queue after all pending messages
     * before (current time + delayMillis). You will receive it in
     * {@link #handleMessage}, in the thread attached to this handler.
     *  
     * @return Returns true if the message was successfully placed in to the 
     *         message queue.  Returns false on failure, usually because the
     *         looper processing the message queue is exiting.  Note that a
     *         result of true does not mean the message will be processed -- if
     *         the looper is quit before the delivery time of the message
     *         occurs then the message will be dropped.
     */
    //其调用了endMessageAtTime，也是将一个消息入队而已，时间靠什么定义而已
    public final boolean sendMessageDelayed(Message msg, long delayMillis)
    {
        if (delayMillis < 0) {
            delayMillis = 0;
        }
        return sendMessageAtTime(msg, SystemClock.uptimeMillis() + delayMillis);
    }

    /***
     * Enqueue a message into the message queue after all pending messages
     * before the absolute time (in milliseconds) <var>uptimeMillis</var>.
     * <b>The time-base is {@link android.os.SystemClock#uptimeMillis}.</b>
     * You will receive it in {@link #handleMessage}, in the thread attached
     * to this handler.
     * 
     * @param uptimeMillis The absolute time at which the message should be
     *         delivered, using the
     *         {@link android.os.SystemClock#uptimeMillis} time-base.
     *         
     * @return Returns true if the message was successfully placed in to the 
     *         message queue.  Returns false on failure, usually because the
     *         looper processing the message queue is exiting.  Note that a
     *         result of true does not mean the message will be processed -- if
     *         the looper is quit before the delivery time of the message
     *         occurs then the message will be dropped.
     */
    //将消息根据时间等入队
    public boolean sendMessageAtTime(Message msg, long uptimeMillis)
    {
        boolean sent = false;
        MessageQueue queue = mQueue;
        if (queue != null) {
            //target对象，嗯
            msg.target = this;
            //将该消息入队
            sent = queue.enqueueMessage(msg, uptimeMillis);
        }
        else {
            RuntimeException e = new RuntimeException(
                this + " sendMessageAtTime() called with no mQueue");
            Log.w("Looper", e.getMessage(), e);
        }
        return sent;
    }

    /***
     * Enqueue a message at the front of the message queue, to be processed on
     * the next iteration of the message loop.  You will receive it in
     * {@link #handleMessage}, in the thread attached to this handler.
     * <b>This method is only for use in very special circumstances -- it
     * can easily starve the message queue, cause ordering problems, or have
     * other unexpected side-effects.</b>
     *  
     * @return Returns true if the message was successfully placed in to the 
     *         message queue.  Returns false on failure, usually because the
     *         looper processing the message queue is exiting.
     */
    public final boolean sendMessageAtFrontOfQueue(Message msg)
    {
        boolean sent = false;
        MessageQueue queue = mQueue;
        if (queue != null) {
            msg.target = this;
            //将该消息入队，且为队首
            sent = queue.enqueueMessage(msg, 0);
        }
        else {
            RuntimeException e = new RuntimeException(
                this + " sendMessageAtTime() called with no mQueue");
            Log.w("Looper", e.getMessage(), e);
        }
        return sent;
    }

    /***
     * Remove any pending posts of messages with code 'what' that are in the
     * message queue.
     */
    public final void removeMessages(int what) {
        mQueue.removeMessages(this, what, null, true);
    }

    /***
     * Remove any pending posts of messages with code 'what' and whose obj is
     * 'object' that are in the message queue.  If <var>token</var> is null,
     * all messages will be removed.
     */
    public final void removeMessages(int what, Object object) {
        mQueue.removeMessages(this, what, object, true);
    }

    /***
     * Remove any pending posts of callbacks and sent messages whose
     * <var>obj</var> is <var>token</var>.  If <var>token</var> is null,
     * all callbacks and messages will be removed.
     */
    public final void removeCallbacksAndMessages(Object token) {
        mQueue.removeCallbacksAndMessages(this, token);
    }

    /***
     * Check if there are any pending posts of messages with code 'what' in
     * the message queue.
     */
    public final boolean hasMessages(int what) {
        return mQueue.removeMessages(this, what, null, false);
    }

    /***
     * Check if there are any pending posts of messages with code 'what' and
     * whose obj is 'object' in the message queue.
     */
    public final boolean hasMessages(int what, Object object) {
        return mQueue.removeMessages(this, what, object, false);
    }

    // if we can get rid of this method, the handler need not remember its loop
    // we could instead export a getMessageQueue() method... 
    public final Looper getLooper() {
        return mLooper;
    }

    public final void dump(Printer pw, String prefix) {
        pw.println(prefix + this + " @ " + SystemClock.uptimeMillis());
        if (mLooper == null) {
            pw.println(prefix + "looper uninitialized");
        } else {
            mLooper.dump(pw, prefix + "  ");
        }
    }

    @Override
    public String toString() {
        return "Handler (" + getClass().getName() + ") {"
        + Integer.toHexString(System.identityHashCode(this))
        + "}";
    }
    //IMessenger是个什么东西，一个远程消息对象，这个可以实现进程间基于消息的通信
    final IMessenger getIMessenger() {
        synchronized (mQueue) {
            if (mMessenger != null) {
                return mMessenger;
            }
            mMessenger = new MessengerImpl();
            return mMessenger;
        }
    }
    //原来在这里，是一个内部类,只实现了一个send方法
    private final class MessengerImpl extends IMessenger.Stub {
        public void send(Message msg) {
            //把handler传递给远程对象，远程对象直接向该handler发送消息，真简单额
            Handler.this.sendMessage(msg);
        }
    }
    //将runnable转换为message,,,,message拥有一个callback，我擦这样啊，变态玩意
    private final Message getPostMessage(Runnable r) {
        Message m = Message.obtain();
        m.callback = r;
        return m;
    }

    private final Message getPostMessage(Runnable r, Object token) {
        Message m = Message.obtain();
        m.obj = token;
        m.callback = r;
        return m;
    }
    //处理消息的回调，调用message的callback的run方法，因为callback是一个runnable
    private final void handleCallback(Message message) {
        message.callback.run();
    }
    //消息队列 消息循环 回调 messenger对象
    //handler是与这些进行绑定的
    final MessageQueue mQueue;
    final Looper mLooper;
    //这个是内部的接口
    final Callback mCallback;
    IMessenger mMessenger;
}