一、理解
Parcelable是一个接口、用来实现序列化。与此类似的还有一个接口Serializable，这是JavaSE本身支持的，而Parcelable是android特有的。二者比较：
1、Parcelable使用起来稍复杂点，而后者使用起来非常简单。下面例子中会看到。
2、Parcelable效率比Serializable高，支持Intent数据传递，也支持进程间通信（IPC）。
3、Parcelable使用时要用到一个Parcel，可以简单将其看为一个容器，序列化时将数据写入Parcel，反序列化时从中取出。
4、在使用内存的时候，Parcelable比Serializable性能高，所以推荐使用Parcelable。Serializable在序列化的时候会产生大量的临时变量，从而引起频繁的GC。Parcelable不能使用在要将数据存储在磁盘上的情况，因为Parcelable在外界有变化的情况下不能很好的保证数据的持续性。尽管Serializable效率低点，但此时还是建议使用Serializable 。
二、源码
结合源码及注释进行理解：
package android.os;
/**
* Interface for classes whose instances can be written to
* and restored from a {@link Parcel}. Classes implementing the Parcelable
* interface must also have a static field called <code>CREATOR</code>, which
* is an object implementing the {@link Parcelable.Creator Parcelable.Creator}
* interface.
*
* <p>A typical implementation of Parcelable is:</p>
*
* <pre>
* public class MyParcelable implements Parcelable {
* private int mData;
*
* public int describeContents() {
* return 0;
* }
*
* public void writeToParcel(Parcel out, int flags) {
* out.writeInt(mData);
* }
*
* public static final Parcelable.Creator<MyParcelable> CREATOR
* = new Parcelable.Creator<MyParcelable>() {
* public MyParcelable createFromParcel(Parcel in) {
* return new MyParcelable(in);
* }
*
* public MyParcelable[] newArray(int size) {
* return new MyParcelable[size];
* }
* };
*
* private MyParcelable(Parcel in) {
* mData = in.readInt();
* }
* }</pre>
*/
public interface Parcelable {
/**
* Flag for use with {@link #writeToParcel}: the object being written
* is a return value, that is the result of a function such as
* "<code>Parcelable someFunction()</code>",
* "<code>void someFunction(out Parcelable)</code>", or
* "<code>void someFunction(inout Parcelable)</code>". Some implementations
* may want to release resources at this point.
*/
public static final int PARCELABLE_WRITE_RETURN_VALUE = 0x0001;
/**
* Bit masks for use with {@link #describeContents}: each bit represents a
* kind of object considered to have potential special significance when
* marshalled.
*/
public static final int CONTENTS_FILE_DESCRIPTOR = 0x0001;
/**
* Describe the kinds of special objects contained in this Parcelable's
* marshalled representation.
*
* @return a bitmask indicating the set of special object types marshalled
* by the Parcelable.
*/
public int describeContents();
/**
* 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}.
*/
public void writeToParcel(Parcel dest, int flags);
/**
* Interface that must be implemented and provided as a public CREATOR
* field that generates instances of your Parcelable class from a Parcel.
*/
public interface Creator<T> {
/**
* 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.
*/
public T createFromParcel(Parcel source);
/**
* Create a new array of the Parcelable class.
*
* @param size Size of the array.
* @return Returns an array of the Parcelable class, with every entry
* initialized to null.
*/
public T[] newArray(int size);
}
/**
* Specialization of {@link Creator} that allows you to receive the
* ClassLoader the object is being created in.
*/
public interface ClassLoaderCreator<T> extends Creator<T> {
/**
* 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()} and
* using the given ClassLoader.
*
* @param source The Parcel to read the object's data from.
* @param loader The ClassLoader that this object is being created in.
* @return Returns a new instance of the Parcelable class.
*/
public T createFromParcel(Parcel source, ClassLoader loader);
}
}
三、示例
Student：
package com.home.testparcelable;
import android.os.Parcel;
import android.os.Parcelable;
public class Student implements Parcelable {
private int id;
private String name;
public Student() {
super();
}
public Student(int id, String name) {
super();
this.id = id;
this.name = name;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public int describeContents() {
return 0;
}
@Override
public void writeToParcel(Parcel dest, int flags) {
// 序列化过程：必须按成员变量声明的顺序进行封装
dest.writeInt(id);
dest.writeString(name);
}
// 反序列过程：必须实现Parcelable.Creator接口，并且对象名必须为CREATOR
// 读取Parcel里面数据时必须按照成员变量声明的顺序，Parcel数据来源上面writeToParcel方法，读出来的数据供逻辑层使用
public static final Parcelable.Creator<Student> CREATOR = new Creator<Student>() {
@Override
public Student createFromParcel(Parcel source) {
return new Student(source.readInt(), source.readString());
}
@Override
public Student[] newArray(int size) {
return new Student[size];
}
};
}
MainActivity：
package com.home.testparcelable;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button btn = (Button) findViewById(R.id.main_btn);
btn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
Intent in = new Intent(MainActivity.this, SecondActivity.class);
in.putExtra("stu", new Student(1, "张三"));
startActivity(in);
}
});
}
}
SecondActivity：
package com.home.testparcelable;
import android.app.Activity;
import android.os.Bundle;
public class SecondActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Student stu = getIntent().getParcelableExtra("stu");
System.out.println("id:" + stu.getId());
System.out.println("name:" + stu.getName());
}
}