android 處理序間通訊資料（一）------parcel的起源，androidparcel

android 處理序間通訊資料（一）------parcel的起源，androidparcel

關於parcel，我們先來講講它的“父輩” Serialize。

Serialize 是java提供的一套序列化機制。但是為什麼要序列化，怎麼序列化，序列化是怎麼做到的，我們將在本文探討下。

一：java 中的serialize

關於Serialize這個東東，think in java其實說的很詳細，大意如下：

1.Serialize的目的

當你建立對象時，你需要，它一直存在，但是當程式終止時，它就消失了。

如果程式不啟動並執行情況下，可以儲存某些資訊，這將非常有用。

如何我程式在下次啟動並執行時候，可以把上次啟動並執行某些資訊恢複回來.

2.Serialize的使用：

 使用一個嵌套的Serializable對象

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();    }        }

驗證序列化的讀寫：

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();        }    }}

最後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 object08-15 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，資料被很好的還原了，包含內部的序列化對象！

 

二：parcel

Serializable是java定義的一套序列化機制，但是他是操作檔案來執行的。或者說，它的效能無法滿足android上的要求，

這樣，parcel被google發明出來，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的內容的傳遞，所以本處做一個簡單的類比：

        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)]

可以看到結果，資料完全正確。

以上就是parcel的使用方式，在下一篇，將探索parcel的實現方式。

 

參考：

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