android Parcelable完全解析

android Parcelable完全解析

title: android.os.Parcelable文檔自譯 date: 2014-12-05 09:16:06

tags:

android.os.Parcelable介面的已知間接子類很多，這裡就不列舉了：

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.

該Interface用於執行個體可以被寫入，並且可以從Parcel中恢複的classes(對於Parcel暫時只要知道它是一個存 放資料的容器就好了，我會在android IPC中寫到它)。實現android.os.Parcelable介面的類必須持有一個實 現了android.os.Parcelable介面的名為 CREATOR 的靜態欄位。

android.os.Parcelable介面典型使用方式,這是官網的例子：

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 CREATOR

= new Parcelable.Creator() {

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(簡介)

Nested Classes(嵌套類)

1.interface Parcelable.ClassLoaderCreator

Specialization of Parcelable.Creator that allows you to receive

the ClassLoader the object is being created in.

 

解析：專業化的 Parcelable.Creator，允許你接收的Object內部建立的 ClassLoader 對象.

 

2.interface Parcelable.Creator

Interface that must be implemented and provided as a public CREATOR field that

generates instances of your Parcelable class from a Parcel.

解析：該介面必須被子類實現，而且CREATOR 作為公有欄位來提供，CREATOR 用於從 Parcel中執行個體化你的可封裝類.

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：用於 describeContents() 的位元遮罩，每一位代表它編組時附加的特殊含義。

 

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)的標誌位：作為一個傳回值，是Parcelable

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

someFunction(inout Parcelable)返回的result。

Public Methods(公用method)

1.abstract int describeContents()

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

representation.

 

解析：描述各種特殊對象，它們包含在可封裝對象的編組形式中.

 

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

Flatten this object in to a Parcel.

 

解析：將該對象展開到Parcel(存放資料的容器)中。

Parcelable適用於通過Intent來傳遞自訂對象。最後給出一個用Parcelable進行資料傳送的例子

1.發送Object的Activity，內容很簡單，點擊Button，Intent攜帶Object跳轉到MainActivity2(用來接收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

* 用來發送資訊的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用來接收來自MainActivity的Object，並列印Person.name的長度和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
• 接收資料的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的實現，具體細節前面已經講到了，就不多說了。

  package me.androiddemo.canglangwenyue.androiddemo;

   

  import android.os.Parcel;

  import android.os.Parcelable;

   

  /**

  * Created by canglangwenyue on 12/5/14.

  * Parcelable常用於Intent中進行自訂對象的傳遞

  */

  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);

   

  }

   

  /*

  需要重寫Creator實現android.os.Parcelable介面的類必須持有一個實現了android.os.Parcelable介面的名為 CREATOR 的靜態欄位

  */

   

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

   

  /*

  重寫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];

  }

   

  };

   

  }

  最後給出在MainActivity2中log列印的結果，眼見為實，哈哈：