Parcelable

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阅读Android源代码时，经常看到使用Parcelable的地方，但是一直没太搞清楚它的作用，今天仔细的看了一下，感觉就是把一堆数据打包，然后传输，然后再分解出来。

public interface Parcelable

如果某个类实现了这个接口，那么它的对象实例可以写入到Parcel中，并且能够从中恢复，并且这个类必须要有一个static的field，并且名称要为CREATOR，这个field是某个实现了Parcelable.Creator接口的类的对象实例。

publicclass MyParcelable implements Parcelable {
privateint mData;

publicint describeContents(){
return0;
}

publicvoid writeToParcel(Parcelout,int flags){
out.writeInt(mData);
}

publicstatic final Parcelable.Creator<MyParcelable> CREATOR
=new Parcelable.Creator<MyParcelable>(){
publicMyParcelable createFromParcel(Parcelin){
returnnew MyParcelable(in);
}

publicMyParcelable[] newArray(int size){
returnnew MyParcelable[size];
}
};

privateMyParcelable(Parcelin){
mData =in.readInt();
}
}

public static interface Parcelable.Creator<T>

Interface that must be implemented and provided as a public CREATOR field that generates instances of your Parcelable class from a Parcel

其有两个成员函数：createFromParcel和newArray。

createFromParcel函数创建实现Parcelable接口的某个类的一个新的对象实例，并且用从给定的Parcel中获取的数据进行实例化，Parcel中的数据是在之前通过Parcelable.writeToParcel方式写入的数据。

newArray函数创建实现Parcelable接口的某个类的一个新的对象数组，数组中的每个项都被初始化为null。

编写了一个简单的程序进行了测试，就是从一个Activity向另外一个Activity传递数据：

PersonMsg.java

package com.example.parcelable;

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

public class PersonMsg implements Parcelable
{
private String name = null;
private int age = 0;

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 int describeContents()
{
  return 0;
}

public void writeToParcel(Parcel out, int flags)
{
  out.writeString(name);
  out.writeInt(age);
}

public static final Parcelable.Creator<PersonMsg> CREATOR =
  new Parcelable.Creator<PersonMsg>()
  {
   public PersonMsg createFromParcel(Parcel in)
   {
    PersonMsg msg = new PersonMsg();
    msg.name = in.readString();
    msg.age = in.readInt();
    return msg;
   }

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

ActivityFrom.java

package com.example.parcelable;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class ActivityFrom extends Activity
{
private EditText nameEditText = null;
private EditText ageEditText = null;
private Button startButton = null;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        nameEditText = (EditText)findViewById(R.id.name_content);
        ageEditText = (EditText)findViewById(R.id.age_content);
        startButton = (Button)findViewById(R.id.start);

        startButton.setOnClickListener(new View.OnClickListener()
        {
   public void onClick(View v)
   {
    String name = nameEditText.getEditableText().toString();
    int age = Integer.valueOf(ageEditText.getEditableText().toString());

    Log.d("name is: ", name);
    Log.d("age is: ", age + "");

    PersonMsg msg = new PersonMsg();
    msg.setName(name);
    msg.setAge(age);

    Intent intent = new Intent();
    intent.setClass(ActivityFrom.this, ActivityTo.class);
    intent.putExtra("personmsg", msg);
    startActivity(intent);
   }
  });
    }
}

ActivityTo.java

package com.example.parcelable;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class ActivityTo extends Activity
{
private EditText nameEditText = null;
private EditText ageEditText = null;
private Button startButton = null;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        nameEditText = (EditText)findViewById(R.id.name_content);
        ageEditText = (EditText)findViewById(R.id.age_content);
        startButton = (Button)findViewById(R.id.start);
        startButton.setVisibility(View.INVISIBLE);

        Intent intent = getIntent();
        PersonMsg msg = (PersonMsg)intent.getParcelableExtra("personmsg");
        String name = msg.getName();
        int age = msg.getAge();

        nameEditText.setText(name);
        ageEditText.setText(age + "");
    }
}

main.xml

<?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"
    >
<LinearLayout
  android:id="@+id/first_row"
  android:layout_width="fill_parent"
  android:layout_height="50dip"
  android:orientation="horizontal"
  >
  <TextView
   android:id="@+id/name_label"
   android:layout_width="60dip"
   android:layout_height="fill_parent"
   android:gravity="center"
   android:text="Name"
   >
  </TextView>
  <EditText
   android:id="@+id/name_content"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   android:gravity="center_vertical|left"
   >
  </EditText>
</LinearLayout>
<LinearLayout
  android:id="@+id/second_row"
  android:layout_width="fill_parent"
  android:layout_height="50dip"
  android:orientation="horizontal"
  >
  <TextView
   android:id="@+id/age_label"
   android:layout_width="60dip"
   android:layout_height="fill_parent"
   android:gravity="center"
   android:text="Age"
   >
  </TextView>
  <EditText
   android:id="@+id/age_content"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   android:gravity="center_vertical|left"
   >
  </EditText>
</LinearLayout>
<Button
  android:id="@+id/start"
  android:layout_width="fill_parent"
  android:layout_height="50dip"
  android:gravity="center"
  android:text="start"
  >
</Button>
</LinearLayout>

实验结果：

点击开始：