Android(安卓)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 intdescribeContents()

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 withdescribeContents(): 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 aParcel. Classes implementing the Parcelable interface must also have a static field calledCREATOR, which is an object implementing theParcelable.Creatorinterface.

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ActivityParcelableTest.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。

public abstract intdescribeContents()

Returns

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