Android Parcelable的介绍与使用

时间：2014-05-09 10:48:02 阅读：411 评论：0 收藏：0 [点我收藏+]

Parcelable使用的一个地方就是在进程间传递一个自定义的较为复杂的对象，对Parcelable学习了一下写下自己的观点。

将一个对象比如说一个名字为Cartoon的自定义类，由一个activity传递到另外一个activity去，这个时候就要用到Parcelable了。首先我们先构建一个bean。

package com.example.sendobjfromactivity.bean;

import android.graphics.Bitmap;

public class Cartoon {
    private Bitmap figure;
    private String name;
    private String creator;
    
    public Bitmap getFigure() {
        return figure;
    }
    public void setFigure(Bitmap figure) {
        this.figure = figure;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getCreator() {
        return creator;
    }
    public void setCreator(String creator) {
        this.creator = creator;
    }
}

这就是我们要传输的数据的格式，下面就思考，要将其在线程间进行传输，就要对其实现序列化，在Android中也就是实现Parcelable接口，这个借口中需要我们实现的主要方法有writeToParcel，describe，ContentsParcelable.Creator<？>。完成完成序列化是依靠writeToParcel方法，而对对象进行反序列化并且返回一个对象实例的是依靠ContentsParcelable.Creator<？>。

下面来看这样一段代码，ParcelableCartoon类实现了Parcelable接口

package com.example.sendobjfromactivity.bean;

import android.graphics.Bitmap;
import android.os.Parcel;
import android.os.Parcelable;
import android.util.Log;

public class ParcelableCartoon implements Parcelable {

    private Cartoon cartoon;
    private static final String MSG = "MESSAGE"; 
    
    public ParcelableCartoon(Cartoon cartoon){
        Log.i(MSG, "ParcelableCartoon::ParcelableCartoon@Cartoon");
        this.cartoon = cartoon;
    }
    
    // 将对象写入Parcel容器中去
    // 完成对对象的序列化
    /**
     * Flatten this object in to a Parcel.
     * 
     * @param dest The Parcel in which the object should be written.
     * @param flags Additional flags about how the object should be written.
     * May be 0 or {@link #PARCELABLE_WRITE_RETURN_VALUE}.
     */
    @Override
    public void writeToParcel(Parcel dest, int flags) {
        Log.i(MSG, "ParcelableCartoon::writeToParcel");
        dest.writeString(cartoon.getName());
        dest.writeString(cartoon.getCreator());
        dest.writeParcelable(cartoon.getFigure(), PARCELABLE_WRITE_RETURN_VALUE);
    }
    
    
    // 完成对序列化的对象反序列化
    public static final Parcelable.Creator<ParcelableCartoon> CREATOR = new Parcelable.Creator<ParcelableCartoon>(){
        // 从Parcel容器中获取序列化的对象，并将其反序列化，得到该对象的实例
        /**
         * Create a new instance of the Parcelable class, instantiating it
         * from the given Parcel whose data had previously been written by
         * {@link Parcelable#writeToParcel Parcelable.writeToParcel()}.
         * 
         * @param source The Parcel to read the object‘s data from.
         * @return Returns a new instance of the Parcelable class.
         */
        @Override
        public ParcelableCartoon createFromParcel(Parcel source) {
            Log.i(MSG, "ParcelableCartoon::Parcelable.Creator::createFromParcel");
            return new ParcelableCartoon(source);
        }

        @Override
        public ParcelableCartoon[] newArray(int size) {
            Log.i(MSG, "ParcelableCartoon::Parcelable.Creator::newArray");
            return new ParcelableCartoon[size];
        }
        
    };
    
    public ParcelableCartoon(Parcel in){
        Log.i(MSG, "ParcelableCartoon::ParcelableCartoon@Parcel");
        cartoon = new Cartoon();
        String name = in.readString();
        
        cartoon.setName(name);
        cartoon.setCreator(in.readString());
        cartoon.setFigure((Bitmap)in.readParcelable(Bitmap.class.getClassLoader()));
    }
    
    public Cartoon getCartoon() {
        Log.i(MSG, "ParcelableCartoon::getCartoon");
        return cartoon;
    }
    
    @Override
    public int describeContents() {
        Log.i(MSG, "ParcelableCartoon::describeContents");
        return 0;
    }
}

在该类中用英文的注释引用了Android文档中的注释。在该类中涉及到一个Parcel，它是一个容器，它的主要任务是对需要序列化的对象进行写入，对需要反序列化的对象进行写出（构造一个实例）。

完成了这些，就可以对对象进行序列化了，也就是说我们可以传递对象了。

下面完成俩个activity，一个负责发送数据，一个用来接收数据。

SendObjFromActivity.java完成发送

package com.example.sendobjfromactivity;

import java.io.InputStream;

import android.app.Activity;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

import com.example.sendobjfromactivity.bean.Cartoon;
import com.example.sendobjfromactivity.bean.ParcelableCartoon;

public class SendObjFromActivity extends Activity {
    
    private Button sendData;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        sendData = (Button)this.findViewById(R.id.button1);
        sendData.setOnClickListener(new OnClickListener(){

            @Override
            public void onClick(View v) {
                Cartoon cartoon = new Cartoon();
                cartoon.setName("Android");
                cartoon.setCreator("Google");
                InputStream is = getResources().openRawResource(R.drawable.ic_launcher);
                Bitmap bitmap = BitmapFactory.decodeStream(is);
                cartoon.setFigure(bitmap);

                Intent intent = new Intent(SendObjFromActivity.this, ReceiveObjActivity.class);
                // 完成对象的序列化操作
                ParcelableCartoon parcelableCartoon = new ParcelableCartoon(cartoon);
                intent.putExtra("msg", parcelableCartoon);
                startActivity(intent);
                
            }});
    }
}

ReceiveObjActivity.java完成对数据的接收

package com.example.sendobjfromactivity;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.widget.ImageView;
import android.widget.TextView;

import com.example.sendobjfromactivity.bean.Cartoon;
import com.example.sendobjfromactivity.bean.ParcelableCartoon;

public class ReceiveObjActivity extends Activity {
    
    private ImageView showImage;
    private TextView showText;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        Log.i("MESSAGE", "进入到了另外的一个activity中去");
        super.onCreate(savedInstanceState);
        setContentView(R.layout.display_obj);
        showImage = (ImageView)this.findViewById(R.id.imageView1);
        showText = (TextView)this.findViewById(R.id.textView1);
        
        Intent intent = getIntent();
        ParcelableCartoon parcelableCartoon = (ParcelableCartoon) intent
                .getParcelableExtra("msg");
        Cartoon cartoon = parcelableCartoon.getCartoon();
        showImage.setImageBitmap(cartoon.getFigure());
        showText.setText(cartoon.getName()+"\n"+cartoon.getCreator());
    }
}