Android example source code file (Message.java)

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Java - Android tags/keywords

android, bundle, can't, classcastexception, creator, handler, max_pool_size, message, messenger, object, os, parcelable, runnable, runtimeexception, stringbuilder

The Message.java Android example source code

/*
 * 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.os.Bundle;
import android.os.Parcel;
import android.os.Parcelable;

/**
 * 
 * Defines a message containing a description and arbitrary data object that can be
 * sent to a {@link Handler}.  This object contains two extra int fields and an
 * extra object field that allow you to not do allocations in many cases.  
 *
 * <p class="note">While the constructor of Message is public, the best way to get
 * one of these is to call {@link #obtain Message.obtain()} or one of the
 * {@link Handler#obtainMessage Handler.obtainMessage()} methods, which will pull
 * them from a pool of recycled objects.</p>
 */
public final class Message implements Parcelable {
    /**
     * User-defined message code so that the recipient can identify 
     * what this message is about. Each {@link Handler} has its own name-space
     * for message codes, so you do not need to worry about yours conflicting
     * with other handlers.
     */
    public int what;

    /**
     * arg1 and arg2 are lower-cost alternatives to using
     * {@link #setData(Bundle) setData()} if you only need to store a
     * few integer values.
     */
    public int arg1; 

    /**
     * arg1 and arg2 are lower-cost alternatives to using
     * {@link #setData(Bundle) setData()} if you only need to store a
     * few integer values.
     */
    public int arg2;

    /**
     * An arbitrary object to send to the recipient.  When using
     * {@link Messenger} to send the message across processes this can only
     * be non-null if it contains a Parcelable of a framework class (not one
     * implemented by the application).   For other data transfer use
     * {@link #setData}.
     * 
     * <p>Note that Parcelable objects here are not supported prior to
     * the {@link android.os.Build.VERSION_CODES#FROYO} release.
     */
    public Object obj;

    /**
     * Optional Messenger where replies to this message can be sent.  The
     * semantics of exactly how this is used are up to the sender and
     * receiver.
     */
    public Messenger replyTo;
    
    /*package*/ long when;
    
    /*package*/ Bundle data;
    
    /*package*/ Handler target;     
    
    /*package*/ Runnable callback;   
    
    // sometimes we store linked lists of these things
    /*package*/ Message next;

    private static Object mPoolSync = new Object();
    private static Message mPool;
    private static int mPoolSize = 0;

    private static final int MAX_POOL_SIZE = 10;
    
    /**
     * Return a new Message instance from the global pool. Allows us to
     * avoid allocating new objects in many cases.
     */
    public static Message obtain() {
        synchronized (mPoolSync) {
            if (mPool != null) {
                Message m = mPool;
                mPool = m.next;
                m.next = null;
                return m;
            }
        }
        return new Message();
    }

    /**
     * Same as {@link #obtain()}, but copies the values of an existing
     * message (including its target) into the new one.
     * @param orig Original message to copy.
     * @return A Message object from the global pool.
     */
    public static Message obtain(Message orig) {
        Message m = obtain();
        m.what = orig.what;
        m.arg1 = orig.arg1;
        m.arg2 = orig.arg2;
        m.obj = orig.obj;
        m.replyTo = orig.replyTo;
        if (orig.data != null) {
            m.data = new Bundle(orig.data);
        }
        m.target = orig.target;
        m.callback = orig.callback;

        return m;
    }

    /**
     * Same as {@link #obtain()}, but sets the value for the <em>target member on the Message returned.
     * @param h  Handler to assign to the returned Message object's <em>target member.
     * @return A Message object from the global pool.
     */
    public static Message obtain(Handler h) {
        Message m = obtain();
        m.target = h;

        return m;
    }

    /**
     * Same as {@link #obtain(Handler)}, but assigns a callback Runnable on
     * the Message that is returned.
     * @param h  Handler to assign to the returned Message object's <em>target member.
     * @param callback Runnable that will execute when the message is handled.
     * @return A Message object from the global pool.
     */
    public static Message obtain(Handler h, Runnable callback) {
        Message m = obtain();
        m.target = h;
        m.callback = callback;

        return m;
    }

    /**
     * Same as {@link #obtain()}, but sets the values for both <em>target and
     * <em>what members on the Message.
     * @param h  Value to assign to the <em>target member.
     * @param what  Value to assign to the <em>what member.
     * @return A Message object from the global pool.
     */
    public static Message obtain(Handler h, int what) {
        Message m = obtain();
        m.target = h;
        m.what = what;

        return m;
    }

    /**
     * Same as {@link #obtain()}, but sets the values of the <em>target, what, and obj
     * members.
     * @param h  The <em>target value to set.
     * @param what  The <em>what value to set.
     * @param obj  The <em>object method to set.
     * @return  A Message object from the global pool.
     */
    public static Message obtain(Handler h, int what, Object obj) {
        Message m = obtain();
        m.target = h;
        m.what = what;
        m.obj = obj;

        return m;
    }

    /**
     * Same as {@link #obtain()}, but sets the values of the <em>target, what, 
     * <em>arg1, and arg2 members.
     * 
     * @param h  The <em>target value to set.
     * @param what  The <em>what value to set.
     * @param arg1  The <em>arg1 value to set.
     * @param arg2  The <em>arg2 value to set.
     * @return  A Message object from the global pool.
     */
    public static Message obtain(Handler h, int what, int arg1, int arg2) {
        Message m = obtain();
        m.target = h;
        m.what = what;
        m.arg1 = arg1;
        m.arg2 = arg2;

        return m;
    }

    /**
     * Same as {@link #obtain()}, but sets the values of the <em>target, what, 
     * <em>arg1, arg2, and obj members.
     * 
     * @param h  The <em>target value to set.
     * @param what  The <em>what value to set.
     * @param arg1  The <em>arg1 value to set.
     * @param arg2  The <em>arg2 value to set.
     * @param obj  The <em>obj value to set.
     * @return  A Message object from the global pool.
     */
    public static Message obtain(Handler h, int what, 
            int arg1, int arg2, Object obj) {
        Message m = obtain();
        m.target = h;
        m.what = what;
        m.arg1 = arg1;
        m.arg2 = arg2;
        m.obj = obj;

        return m;
    }

    /**
     * Return a Message instance to the global pool.  You MUST NOT touch
     * the Message after calling this function -- it has effectively been
     * freed.
     */
    public void recycle() {
        synchronized (mPoolSync) {
            if (mPoolSize < MAX_POOL_SIZE) {
                clearForRecycle();
                
                next = mPool;
                mPool = this;
            }
        }
    }

    /**
     * Make this message like o.  Performs a shallow copy of the data field.
     * Does not copy the linked list fields, nor the timestamp or
     * target/callback of the original message.
     */
    public void copyFrom(Message o) {
        this.what = o.what;
        this.arg1 = o.arg1;
        this.arg2 = o.arg2;
        this.obj = o.obj;
        this.replyTo = o.replyTo;

        if (o.data != null) {
            this.data = (Bundle) o.data.clone();
        } else {
            this.data = null;
        }
    }

    /**
     * Return the targeted delivery time of this message, in milliseconds.
     */
    public long getWhen() {
        return when;
    }
    
    public void setTarget(Handler target) {
        this.target = target;
    }

    /**
     * Retrieve the a {@link android.os.Handler Handler} implementation that
     * will receive this message. The object must implement
     * {@link android.os.Handler#handleMessage(android.os.Message)
     * Handler.handleMessage()}. Each Handler has its own name-space for
     * message codes, so you do not need to
     * worry about yours conflicting with other handlers.
     */
    public Handler getTarget() {
        return target;
    }

    /**
     * Retrieve callback object that will execute when this message is handled.
     * This object must implement Runnable. This is called by
     * the <em>target {@link Handler} that is receiving this Message to
     * dispatch it.  If
     * not set, the message will be dispatched to the receiving Handler's
     * {@link Handler#handleMessage(Message Handler.handleMessage())}.
     */
    public Runnable getCallback() {
        return callback;
    }
    
    /** 
     * Obtains a Bundle of arbitrary data associated with this
     * event, lazily creating it if necessary. Set this value by calling
     * {@link #setData(Bundle)}.  Note that when transferring data across
     * processes via {@link Messenger}, you will need to set your ClassLoader
     * on the Bundle via {@link Bundle#setClassLoader(ClassLoader)
     * Bundle.setClassLoader()} so that it can instantiate your objects when
     * you retrieve them.
     * @see #peekData()
     * @see #setData(Bundle)
     */
    public Bundle getData() {
        if (data == null) {
            data = new Bundle();
        }
        
        return data;
    }

    /** 
     * Like getData(), but does not lazily create the Bundle.  A null
     * is returned if the Bundle does not already exist.  See
     * {@link #getData} for further information on this.
     * @see #getData()
     * @see #setData(Bundle)
     */
    public Bundle peekData() {
        return data;
    }

    /**
     * Sets a Bundle of arbitrary data values. Use arg1 and arg1 members 
     * as a lower cost way to send a few simple integer values, if you can.
     * @see #getData() 
     * @see #peekData()
     */
    public void setData(Bundle data) {
        this.data = data;
    }

    /**
     * Sends this Message to the Handler specified by {@link #getTarget}.
     * Throws a null pointer exception if this field has not been set.
     */
    public void sendToTarget() {
        target.sendMessage(this);
    }

    /*package*/ void clearForRecycle() {
        what = 0;
        arg1 = 0;
        arg2 = 0;
        obj = null;
        replyTo = null;
        when = 0;
        target = null;
        callback = null;
        data = null;
    }

    /** Constructor (but the preferred way to get a Message is to call {@link #obtain() Message.obtain()}).
    */
    public Message() {
    }

    public String toString() {
        StringBuilder   b = new StringBuilder();
        
        b.append("{ what=");
        b.append(what);

        b.append(" when=");
        b.append(when);

        if (arg1 != 0) {
            b.append(" arg1=");
            b.append(arg1);
        }

        if (arg2 != 0) {
            b.append(" arg2=");
            b.append(arg2);
        }

        if (obj != null) {
            b.append(" obj=");
            b.append(obj);
        }

        b.append(" }");
        
        return b.toString();
    }

    public static final Parcelable.Creator<Message> CREATOR
            = new Parcelable.Creator<Message>() {
        public Message createFromParcel(Parcel source) {
            Message msg = Message.obtain();
            msg.readFromParcel(source);
            return msg;
        }
        
        public Message[] newArray(int size) {
            return new Message[size];
        }
    };
        
    public int describeContents() {
        return 0;
    }

    public void writeToParcel(Parcel dest, int flags) {
        if (callback != null) {
            throw new RuntimeException(
                "Can't marshal callbacks across processes.");
        }
        dest.writeInt(what);
        dest.writeInt(arg1);
        dest.writeInt(arg2);
        if (obj != null) {
            try {
                Parcelable p = (Parcelable)obj;
                dest.writeInt(1);
                dest.writeParcelable(p, flags);
            } catch (ClassCastException e) {
                throw new RuntimeException(
                    "Can't marshal non-Parcelable objects across processes.");
            }
        } else {
            dest.writeInt(0);
        }
        dest.writeLong(when);
        dest.writeBundle(data);
        Messenger.writeMessengerOrNullToParcel(replyTo, dest);
    }

    private final void readFromParcel(Parcel source) {
        what = source.readInt();
        arg1 = source.readInt();
        arg2 = source.readInt();
        if (source.readInt() != 0) {
            obj = source.readParcelable(getClass().getClassLoader());
        }
        when = source.readLong();
        data = source.readBundle();
        replyTo = Messenger.readMessengerOrNullFromParcel(source);
    }
}