android 进程间通信数据（一）------parcel的起源

关于parcel，我们先来讲讲它的“父辈” Serialize。

Serialize 是java提供的一套序列化机制。但是为什么要序列化，怎么序列化，序列化是怎么做到的，我们将在本文探讨下。

一：java 中的serialize

关于Serialize这个东东，think in java其实说的很详细，大意如下：

1.Serialize的目的

当你创建对象时，你需要，它一直存在，但是当程序终止时，它就消失了。

如果程序不运行的情况下，可以保存某些信息，这将非常有用。

如何我程序在下次运行的时候，可以把上次运行的某些信息恢复回来.

2.Serialize的使用：

使用一个嵌套的Serializable对象

package com.joyfulmath.androidstudy.bind.worm;

import java.io.Serializable;

public class Data implements Serializable {

    private int n;

    public Data(int n) {
        this.n = n;
    }

    @Override
    public String toString() {
        return Integer.toString(n);
    }

}

package com.joyfulmath.androidstudy.bind.worm;

import java.io.Serializable;
import java.util.Random;

import com.joyfulmath.androidstudy.TraceLog;

public class Worm implements Serializable {
    static Random rand = new Random(47);
    Data[] d = {
            new Data(rand.nextInt(10)),
            new Data(rand.nextInt(10)),
            new Data(rand.nextInt(10))
    };

    private Worm next;
    private char c;

    public Worm(int i, char x)
    {
        TraceLog.i("Worm construct:"+i);
        c = x;
        if(--i>0)
        {
            next = new Worm(i,(char) (x+1));
        }
    }

    public Worm()
    {
        TraceLog.i("default Worm construct");
    }

    @Override
    public String toString() {
        StringBuilder result = new StringBuilder(":");
        result.append(c);
        result.append("(");
        for(Data dat:d)
        {
            result.append(dat+" ");
        }
        result.append(")");
        if(next!=null)
        {
            result.append(next);
        }
        return result.toString();
    }

}

验证序列化的读写：

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

import com.joyfulmath.androidstudy.TraceLog;

public class WormSample {

    static final String path = "/mnt/sdcard/worm.out";
    public void doAction()
    {
        Worm w = new Worm(6, 'a');
        TraceLog.i("\n"+w.toString());

        try {
            ObjectOutputStream opt = new ObjectOutputStream(new FileOutputStream(path));
            opt.writeObject("Worm object\n");
            opt.writeObject(w);
            opt.close();
            ObjectInputStream in = new ObjectInputStream(new FileInputStream(path));
            String s = (String) in.readObject();
            Worm w2 = (Worm) in.readObject();
            TraceLog.i(s+w);
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

最后log：

08-15 09:18:20.384: I/Worm(28437): <init>: Worm construct:6 [at (Worm.java:21)]
08-15 09:18:20.384: I/Worm(28437): <init>: Worm construct:5 [at (Worm.java:21)]
08-15 09:18:20.384: I/Worm(28437): <init>: Worm construct:4 [at (Worm.java:21)]
08-15 09:18:20.384: I/Worm(28437): <init>: Worm construct:3 [at (Worm.java:21)]
08-15 09:18:20.384: I/Worm(28437): <init>: Worm construct:2 [at (Worm.java:21)]
08-15 09:18:20.384: I/Worm(28437): <init>: Worm construct:1 [at (Worm.java:21)]
08-15 09:18:20.384: I/WormSample(28437): doAction:
08-15 09:18:20.384: I/WormSample(28437): :a(853):b(119):c(802):d(788):e(199):f(881) [at (WormSample.java:18)]
08-15 09:18:20.414: I/WormSample(28437): doAction: Worm object
08-15 09:18:20.414: I/WormSample(28437): :a(853):b(119):c(802):d(788):e(199):f(881) [at (WormSample.java:28)]

可以看到，数据被很好的还原了，包含内部的序列化对象！

二：parcel

Serializable是java定义的一套序列化机制，但是他是操作文件来执行的。或者说，它的性能无法满足android上的要求，

这样，parcel被google发明出来，用以取代Serializable。

1.Parcelable 的使用

package com.joyfulmath.androidstudy.bind.worm;

import android.os.Parcel;
import android.os.Parcelable;

public class DataP implements Parcelable {

    public int n;

    public DataP(int n) {
        this.n = n;
    }

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeInt(n);
    }

    public static final Parcelable.Creator<DataP> CREATOR = new Parcelable.Creator<DataP>()
    {
        public DataP createFromParcel(Parcel in)
        {
            return new DataP(in);
        }

        public DataP[] newArray(int size)
        {
            return new DataP[size];
        }
    };

    private DataP(Parcel in)
    {
        n = in.readInt();
    }

    @Override
    public String toString() {
        return Integer.toString(n);
    }

}

package com.joyfulmath.androidstudy.bind.worm;

import java.util.Random;

import com.joyfulmath.androidstudy.TraceLog;

import android.os.Parcel;
import android.os.Parcelable;

public class WormP implements Parcelable {

    static Random rand = new Random(47);
    public DataP[] d = { new DataP(rand.nextInt(10)), new DataP(rand.nextInt(10)),
            new DataP(rand.nextInt(10)) };

    private WormP next;
    public byte c;

    public WormP(int i,byte x)
    {
        TraceLog.i("Wormp construct:"+i);
        c = x;
        if(--i>0)
        {
            next = new WormP(i,(byte) (x+1));
        }
    }

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeByte(c);
        dest.writeParcelableArray(d, 0);
        if (next != null) {
            dest.writeParcelable(next, 0);
        }
    }

    public static final Parcelable.Creator<WormP> CREATOR = new Parcelable.Creator<WormP>() {
        public WormP createFromParcel(Parcel in) {
            return new WormP(in);
        }

        public WormP[] newArray(int size) {
            return new WormP[size];
        }
    };

    private WormP(Parcel in) {
        c = in.readByte();
        d = (DataP[]) in.readParcelableArray(DataP.class.getClassLoader());
    }

    @Override
    public String toString() {
        StringBuilder result = new StringBuilder(":");
        result.append(c);
        result.append("(");
        for(DataP dat:d)
        {
            result.append(dat+" ");
        }
        result.append(")");
        if(next!=null)
        {
            result.append(next);
        }
        return result.toString();
    }
}

parcel一般使用在intent的内容的传递，所以本处做一个简单的模拟：

    public void doActionP()
    {
        TraceLog.i();
        byte a = 'a';
        WormP w = new WormP(6, a);
        TraceLog.i(w.toString());
        Intent intent = new Intent();
        intent.putExtra("wormp", w);

        ///...

        Intent newIntent = new Intent(intent);

        WormP w2 = newIntent.getParcelableExtra("wormp");
        TraceLog.i(w2.toString());

        TraceLog.i("end");
    }

08-15 10:14:11.924: I/WormSample(20183): doActionP:  [at (WormSample.java:47)]
08-15 10:14:11.934: I/WormP(20183): <init>: Wormp construct:6 [at (WormP.java:21)]
08-15 10:14:11.934: I/WormP(20183): <init>: Wormp construct:5 [at (WormP.java:21)]
08-15 10:14:11.934: I/WormP(20183): <init>: Wormp construct:4 [at (WormP.java:21)]
08-15 10:14:11.934: I/WormP(20183): <init>: Wormp construct:3 [at (WormP.java:21)]
08-15 10:14:11.934: I/WormP(20183): <init>: Wormp construct:2 [at (WormP.java:21)]
08-15 10:14:11.934: I/WormP(20183): <init>: Wormp construct:1 [at (WormP.java:21)]
08-15 10:14:11.934: I/WormSample(20183): doActionP: :97(8 5 3 ):98(1 1 9 ):99(8 0 2 ):100(7 8 8 ):101(1 9 9 ):102(8 8 1 ) [at (WormSample.java:50)]
08-15 10:14:11.934: I/WormSample(20183): doActionP: :97(8 5 3 ):98(1 1 9 ):99(8 0 2 ):100(7 8 8 ):101(1 9 9 ):102(8 8 1 ) [at (WormSample.java:59)]
08-15 10:14:11.934: I/WormSample(20183): doActionP: end [at (WormSample.java:61)]

可以看到结果，数据完全正确。

以上就是parcel的使用方式，在下一篇，将探索parcel的实现方式。

参考：

http://blog.csdn.net/niu_gao/article/details/6451699