Android 中Parcelable的作用 (转载)

android提供了一种新的类型：Parcel。本类被用作封装数据的容器，封装后的数据可以通过Intent或IPC传递。 除了基本类型以

外，只有实现了Parcelable接口的类才能被放入Parcel中。

 

Parcelable实现要点：需要实现三个东西

1）writeToParcel 方法。该方法将类的数据写入外部提供的Parcel中.声明如下：

writeToParcel (Parcel dest, int flags) 具体参数含义见javadoc

2）describeContents方法。（没搞懂有什么用，反正直接返回0也可以）

官方网站解释：

public abstract int describeContents ()

Describe the kinds of special objects contained in this Parcelable's marshalled representation.

Returns

• a bitmask indicating the set of special object types marshalled by the Parcelable.

按照官方文档的解释一般是与CONTENTS_FILE_DESCRIPTOR 一起用，CONTENTS_FILE_DESCRIPTOR常量以二进制形式表示，每一位可以代表一个特使的对象

Bit masks for use with describeContents(): each bit represents a kind of object considered to have potential special significance when marshalled.

3）静态的Parcelable.Creator接口，本接口有两个方法：

createFromParcel(Parcel in) 实现从in中创建出类的实例的功能

newArray(int size) 创建一个类型为T，长度为size的数组，仅一句话（return new T[size])即可。估计本方法是供外部类反序列化本类数组使用。

测试用的接收信息Activity

import android.app.Activity;   
 
import android.content.Intent;   
 
import android.os.Bundle;   
import android.os.Parcelable;   
  
public class Test extends Activity {   
      
    @Override  
    public void onCreate(Bundle savedInstanceState) {   
        super.onCreate(savedInstanceState);   
        setContentView(R.layout.main);   
        Intent i = getIntent();   
        Person p = i.getParcelableExtra("yes");   
        System.out.println("---->"+p.name);   
        System.out.println("---->"+p.map.size());   
    }   
}  

发送的Activity

import java.util.HashMap;   
  
import android.app.Activity;   
import android.content.Intent;   
import android.os.Bundle;   
  
public class TestNew extends Activity {   
      
    @Override  
    public void onCreate(Bundle savedInstanceState) {   
        super.onCreate(savedInstanceState);   
        setContentView(R.layout.main);   
        Intent intent = new Intent();   
        Person p = new Person();   
        p.map = new HashMap<String,String>();   
        p.map.put("yes", "ido");   
        p.name="ok";   
        intent.putExtra("yes", p);   
        intent.setClass(this, Test.class);   
        startActivity(intent);   
    }   
}  

Parcelable的实现类

 

import java.util.HashMap;   
  
import android.os.Parcel;   
import android.os.Parcelable;   
  
public class Person implements Parcelable {   
  
    public HashMap<String,String> map = new HashMap<String,String> ();   
       
    public String name ;   
    @Override  
    public int describeContents() {   
        return 0;   
    }   
  
    @Override  
    public void writeToParcel(Parcel dest, int flags) {   
  
        dest.writeMap(map);   
        dest.writeString(name);   
    }   
    public static final Parcelable.Creator<Person> CREATOR = new Parcelable.Creator<Person>() {   
//重写Creator
  
        @Override  
        public Person createFromParcel(Parcel source) {   
            Person p = new Person();   
            p.map=source.readHashMap(HashMap.class.getClassLoader());   
            p.name=source.readString();   
            return p;   
        }   
  
        @Override  
        public Person[] newArray(int size) {   
            // TODO Auto-generated method stub   
            return null;   
        }   
    };   
  
}  

下面写一下转载自http://blog.csdn.net/zyc13701469860/article/details/6429934的对Parcel的解说：

在SDK中 Parcelable类的概述是这样的：Interface for classes whose instances can be written to and restored from a Parcel. Classes implementing the Parcelable interface must also have a static field called CREATOR, which is an object implementing theParcelable.Creator interface.

 

这个接口的实例是通过Parcel进行存储的，在使用Parcelable的时候必须使用Parcelable.Creator。

 

下面上代码：

首先修改main.xml，增加一个button

<?xml version="1.0" encoding="utf-8"?>  
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"  
    android:orientation="vertical"  
    android:layout_width="fill_parent"  
    android:layout_height="fill_parent"  
    >  
<TextView    
android:id="@+id/text"  
    android:layout_width="fill_parent"   
    android:layout_height="wrap_content"   
    android:text="@string/hello"  
    />  
<Button  
android:id="@+id/button"  
    android:layout_width="wrap_content"   
    android:layout_height="wrap_content"   
    android:text="Parcelable">  
</Button>  
</LinearLayout> 

然后是主Activity ParcelableTest.java,这个类显示UI，并通过button点击事件启动另一个Activity -- ParcelableTest2,同时通过Parcelable接口传递一些数据。

package parcelable_test.com;  
   
import android.app.Activity;  
import android.content.Intent;  
import android.os.Bundle;  
import android.util.Log;  
import android.view.View;  
import android.view.View.OnClickListener;  
import android.widget.Button;  
   
public class ParcelableTest extends Activity implements OnClickListener{  
public static final String KEY = "key";  
private Button button;  
public static final String TAG = "Parcelable";   
   
@Override  
public void onCreate(Bundle savedInstanceState) {    
        super.onCreate(savedInstanceState);    
        setContentView(R.layout.main);  
        init();  
        Log.d(TAG, "ParcelableTest");  
    }   
   
private void init(){  
button = (Button)findViewById(R.id.button);  
button.setOnClickListener(this);  
}  
   
private void fun(){  
Log.d(TAG, "fun");  
Person mPerson = new Person();  
mPerson.setName("tom");  
mPerson.setAge(25);  
Intent mIntent = new Intent(this,parcelable_test.com.ParcelableTest2.class);  
Bundle mBundle = new Bundle();  
mBundle.putParcelable(KEY, mPerson);  
mIntent.putExtras(mBundle);  
startActivity(mIntent);  
}  
   
@Override  
public void onClick(View v) {  
switch (v.getId()) {  
case R.id.button:  
fun();  
break;  
   
default:  
break;  
}  
}  
}

ParcelableTest2.java,这个类用于获取ParcelableTest传出的数据，并显示在UI上。

package parcelable_test.com;  
   
import android.app.Activity;  
import android.os.Bundle;  
import android.util.Log;  
import android.widget.TextView;  
   
public class ParcelableTest2 extends Activity{  
private static final String TAG = ParcelableTest.TAG;  
@Override  
public void onCreate(Bundle savedInstanceState) {    
        super.onCreate(savedInstanceState);    
        setContentView(R.layout.main);       
        Log.d(TAG, "ParcelableTest2");  
        TextView textView = new TextView(this);  
        Person mPerson = (Person)getIntent().getParcelableExtra(ParcelableTest.KEY);  
        textView.setText("name = " + mPerson.getName() + "  age = " + mPerson.getAge());  
        setContentView(textView);  
    }   
}

下面就是最重要的类Person,Person类引用了Parcelable接口

package parcelable_test.com;  
import android.os.Parcel;    
import android.os.Parcelable;   
import android.util.Log;  
public class Person implements Parcelable{  
private String name;  
private int age;  
private static final String TAG = ParcelableTest.TAG;   
public String getName() {  
return name;  
}  
public void setName(String name) {  
this.name = name;  
}  
public int getAge() {  
return age;  
}  
public void setAge(int age) {  
this.age = age;  
}  
public static final Parcelable.Creator<Person> CREATOR = new Creator<Person>() {  
@Override  
public Person createFromParcel(Parcel source) {  
Log.d(TAG,"createFromParcel");  
Person mPerson = new Person();  
mPerson.name = source.readString();  
mPerson.age = source.readInt();  
return mPerson;  
}  
@Override  
public Person[] newArray(int size) {  
// TODO Auto-generated method stub  
return new Person[size];  
}  
};  
@Override  
public int describeContents() {  
// TODO Auto-generated method stub  
Log.d(TAG,"describeContents");  
return 0;  
}  
@Override  
public void writeToParcel(Parcel dest, int flags) {  
// TODO Auto-generated method stub  
Log.d(TAG,"writeToParcel");  
dest.writeString(name);  
dest.writeInt(age);  
}  
}  

通过log可知程序的运行情况，在mBundle.putParcelable(KEY, mPerson);时，调用了Person类中的public void writeToParcel(Parcel dest, int flags)方法，并向dest写数据，在 Person mPerson = (Person)getIntent().getParcelableExtra(ParcelableTest.KEY);的时候，调用了Person类中的public Person createFromParcel(Parcel source) 方法，创建了一个Person对象，并给这个对象的属性赋值，这里的Parcel source和Parcel dest,是相同的，然后返回这个Person对象。最后就可以打印出mPerson的属性信息了。

Parcel可以用来存放很多数据，比如都是String和int，又或者有一个String和HashMap<String,String>的集合，都很方便。