android parcelable 详细介绍

想要在两个activity之间传递对象，那么这个对象必须序列化，Android中序列化一个对象有两种方式，一种是实现Serializable接口，这个非常简单，只需要声明一下就可以了，不痛不痒。但是android中还有一种特有的序列化方法，那就是实现Parcelable接口，使用这种方式来序列化的效率要高于实现Serializable接口。不过Serializable接口实在是太方便了，因此在某些情况下实现这个接口还是非常不错的选择。
使用Parcelable步骤：
1.实现Parcelable接口
2.实现接口中的两个方法

public int describeContents();
public void writeToParcel(Parcel dest, int flags);

第一个方法是内容接口描述，默认返回0就可以了
第二个方法是将我们的对象序列化一个Parcel对象，也就是将我们的对象存入Parcel中
3.实例化静态内部对象CREATOR实现接口Parcelable.Creator，实例化CREATOR时要实现其中的两个方法，其中createFromParcel的功能就是从Parcel中读取我们的对象。

也就是说我们先利用writeToParcel方法写入对象，再利用createFromParcel方法读取对象，因此这两个方法中的读写顺序必须一致，否则会出现数据紊乱，一会我会举例子。
看一个代码示例：

public class Person implements Parcelable{private String username;private String nickname;private int age;public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getNickname() {return nickname;}public void setNickname(String nickname) {this.nickname = nickname;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public Person(String username, String nickname, int age) {super();this.username = username;this.nickname = nickname;this.age = age;}public Person() {super();}/*** 这里的读的顺序必须与writeToParcel(Parcel dest, int flags)方法中* 写的顺序一致，否则数据会有差错，比如你的读取顺序如果是：* nickname = source.readString();* username=source.readString();* age = source.readInt();* 即调换了username和nickname的读取顺序，那么你会发现你拿到的username是nickname的数据，* 而你拿到的nickname是username的数据* @param source*/public Person(Parcel source) {username = source.readString();nickname=source.readString();age = source.readInt();}/*** 这里默认返回0即可*/@Overridepublic int describeContents() {return 0;}/*** 把值写入Parcel中*/@Overridepublic void writeToParcel(Parcel dest, int flags) {dest.writeString(username);dest.writeString(nickname);dest.writeInt(age);}public static final Creator<Person> CREATOR = new Creator<Person>() {/*** 供外部类反序列化本类数组使用*/@Overridepublic Person[] newArray(int size) {return new Person[size];}/*** 从Parcel中读取数据*/@Overridepublic Person createFromParcel(Parcel source) {return new Person(source);}};
}

最后贴上Parcelable源码，Google已经给了一个示例了：

/** Copyright (C) 2006 The Android Open Source Project** Licensed under the Apache License, Version 2.0 (the "License");* you may not use this file except in compliance with the License.* You may obtain a copy of the License at**      http://www.apache.org/licenses/LICENSE-2.0** Unless required by applicable law or agreed to in writing, software* distributed under the License is distributed on an "AS IS" BASIS,* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.* See the License for the specific language governing permissions and* limitations under the License.*/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&lt;MyParcelable&gt; CREATOR*             = new Parcelable.Creator&lt;MyParcelable&gt;() {*         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);}
}

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