android中Parcelable接口的使用

1. 简介

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、源码解析

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类:

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, "李四"));                  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());      }  }