android Parcelable完全解析

title: android.os.Parcelable文档自译 date: 2014-12-05 09:16:06

tags:

android.os.Parcelable接口的已知间接子类很多,这里就不列举了:

Class Overview


Interface for classes whose instances can be written to and restored from a 

Parcel. Classes implementing the Parcelable interface must also have a static 

field called CREATOR, which is an object implementing the Parcelable.Creator 

interface.

该Interface用于实例可以被写入,并且可以从Parcel中恢复的classes(对于Parcel暂时只要知道它是一个存 放数据的容器就好了,我会在android IPC中写到它)。实现android.os.Parcelable接口的类必须持有一个实 现了android.os.Parcelable接口的名为 CREATOR 的静态字段。

android.os.Parcelable接口典型使用方式,这是官网的例子:

package me.androiddemo.canglangwenyue.androiddemo;


import android.os.Parcel;

import android.os.Parcelable;


/**

 * Created by canglangwenyue on 12/5/14.

*/

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();

}

}

Summary(简介)

Nested Classes(嵌套类)

1.interface Parcelable.ClassLoaderCreator<T>

    Specialization of Parcelable.Creator that allows you to receive

    the ClassLoader the object is being created in.


解析:专业化的 Parcelable.Creator,允许你接收的Object内部创建的 ClassLoader 对象. 


2.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. 

 解析:该接口必须被子类实现,而且CREATOR 作为公有字段来提供,CREATOR 用于从 Parcel中实例化你的可包装类.

Constants(常量)

1.int   CONTENTS_FILE_DESCRIPTOR     

Bit masks for use with describeContents(): each bit represents a kind of object

 considered to have potential special significance when marshalled.


解析:用于 describeContents() 的位掩码,每一位代表它编组时附加的特殊含义。


2.int   PARCELABLE_WRITE_RETURN_VALUE    

Flag for use with writeToParcel(Parcel, int): the object being written is a 

return value, that is the result of a function such as "Parcelable 

someFunction()", "void someFunction(out Parcelable)", or "void 

someFunction(inout Parcelable)".


解析:writeToParcel(Parcel, int)的标志位:作为一个返回值,是"Parcelable 

someFunction()", "void someFunction(out Parcelable)", or "void 

someFunction(inout Parcelable)"返回的result。

Public Methods(公共method)

1.abstract int   describeContents()

Describe the kinds of special objects contained in this Parcelable‘s marshalled

 representation.


 解析:描述各种特殊对象,它们包含在可包装对象的编组形式中.


2.abstract void  writeToParcel(Parcel dest, int flags)

Flatten this object in to a Parcel.


解析:将该对象展开到Parcel(存放数据的容器)中。

Parcelable适用于通过Intent来传递自定义对象。最后给出一个用Parcelable进行数据传送的例子

1.发送Object的Activity,内容很简单,点击Button,Intent携带Object跳转到MainActivity2(用来接收Object的Activity)。

package me.androiddemo.canglangwenyue.androiddemo;


import android.content.Intent;

import android.support.v7.app.ActionBarActivity;

import android.os.Bundle;

import android.view.Menu;

import android.view.MenuItem;

import android.view.View;

import android.widget.Button;


import java.util.HashMap;


/**

* @author canglangwenyue

* 用来发送信息的Activity

 */


public class MainActivity extends ActionBarActivity {


private Button sendButton;


@Override

protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_main);


    sendButton = (Button) findViewById(R.id.send_button);


    sendButton.setOnClickListener(new View.OnClickListener() {

        @Override

        public void onClick(View v) {

            Intent intent = new Intent();

            Person person = new Person();


            person.name = "WenYue";

            intent.putExtra("WenYue",person);

            intent.setClass(MainActivity.this,MainActivity2.class);


            startActivity(intent);

        }

    });


}



@Override

public boolean onCreateOptionsMenu(Menu menu) {

    // Inflate the menu; this adds items to the action bar if it is present.

    getMenuInflater().inflate(R.menu.menu_main, menu);

    return true;

}


@Override

public boolean onOptionsItemSelected(MenuItem item) {

    // Handle action bar item clicks here. The action bar will

    // automatically handle clicks on the Home/Up button, so long

    // as you specify a parent activity in AndroidManifest.xml.

    int id = item.getItemId();


    //noinspection SimplifiableIfStatement

    if (id == R.id.action_settings) {

        return true;

    }


    return super.onOptionsItemSelected(item);

}

}

2.MainActivity2用来接收来自MainActivity的Object,并打印Person.name的长度和content。

package me.androiddemo.canglangwenyue.androiddemo;


import android.content.Intent;

import android.support.v7.app.ActionBarActivity;

import android.os.Bundle;

import android.util.Log;

import android.view.Menu;

import android.view.MenuItem;


/**

  • @author canglangwenyue
  • 接收数据的Intent */
    public class MainActivity2 extends ActionBarActivity {
    @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main_activity2);
     Intent intent = getIntent();
  • Person person = intent.getParcelableExtra("WenYue");
  • Log.e("MainActivity2 received message‘s length----->",String.valueOf(person.name.length()));
  • Log.e("MainActivity2 received message content------>",person.name);

  • }
    @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.menu_main_activity2, menu); return true; }
    @Override public boolean onOptionsItemSelected(MenuItem item) { // Handle action bar item clicks here. The action bar will // automatically handle clicks on the Home/Up button, so long // as you specify a parent activity in AndroidManifest.xml. int id = item.getItemId();
     //noinspection SimplifiableIfStatement
  • if (id == R.id.action_settings) {
  •     return true;
  • }
  • return super.onOptionsItemSelected(item);

  • } }

3.Parcelable的实现,具体细节前面已经讲到了,就不多说了。

package me.androiddemo.canglangwenyue.androiddemo;


import android.os.Parcel;

import android.os.Parcelable;


/**

* Created by canglangwenyue on 12/5/14.

* Parcelable常用于Intent中进行自定义对象的传递

*/

public class Person implements Parcelable {



public String name;


@Override

public int describeContents() {

    return 0;

}


@Override

public void writeToParcel(Parcel dest, int flags) {


    dest.writeString(name);


}


/*

需要重写Creator实现android.os.Parcelable接口的类必须持有一个实现了android.os.Parcelable接口的名为 CREATOR 的静态字段

 */


public static final Creator<Person> CREATOR = new Parcelable.Creator<Person>() {


    /*

    重写Creator方法

     */

    @Override

    public Person createFromParcel(Parcel source) {

        Person person = new Person();

        person.name = source.readString();

        return person;

    }


    @Override

    public Person[] newArray(int size) {

        return new Person[0];

    }


};


}

最后给出在MainActivity2中log打印的结果,眼见为实,哈哈:


再附上demo下载地址,希望对大家与帮助: 苍狼问月

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