android开发之Parcelable使用详解

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 */    @Override    public int describeContents() {        return 0;    }    /** * 把值写入Parcel中 */    @Override    public 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 */        @Override        public Person[] newArray(int size) {            return new Person[size];        }        /** * 从Parcel中读取数据 */        @Override        public Person createFromParcel(Parcel source) {            return new Person(source);        }    };}

本工程源码http://pan.baidu.com/s/1hqzY3go

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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