Android 用Intent 傳遞對象之 Parcel

Android 為對象序列化開發了 Parcelable 接口，這個接口要比之前說的 Serializable 更為高效。使用會稍微複雜些。

其主要思想就是把 對象需要儲存的資料 放在 parcel 對象中，然後再從 parcel 中恢複這個對象。可見實作 Parcelable這個接口的類，至少會實作兩個方法一個用來 将資料儲存進 parcel 對象，一個 方法用來從 parcel 中恢複對象。

示例結構：

 先寫一個實作了 Parcelable 接口的類 Person，可見 writeToParcel 用來向Parcel 對象寫入要儲存的對象，

CREATOR 用來恢複對象。存入的資料要和讀取的資料順序對應。

package com.serializabletest;

import android.os.Parcel;
import android.os.Parcelable;
import android.util.Log;

class Person implements Parcelable {

  private static final String TAG = "Person";
  int ID;
  String Name;
  int age;

  public Person(int ID, String Name, int age) {
    this.ID = ID;
    this.Name = Name;
    this.age = age;
  }

  public void printPerson() {
    Log.d(TAG, "ID:" + ID);
    Log.d(TAG, "Name:" + Name);
    Log.d(TAG, "age:" + age);
  }

  // -------------------------------------------------
  public Person(Parcel in) {
    this.ID = in.readInt();
    this.Name = in.readString();
    this.age = in.readInt();
  }

  // 從 Parcel 對象 中恢複 Person 對象
  <span style="color:#ff0000;"><strong>public static final Parcelable.Creator<Person> CREATOR</strong> </span>= new Parcelable.Creator<Person>() {

    @Override
    public Person createFromParcel(Parcel arg0) {
      // TODO Auto-generated method stub
      return new Person(arg0);
    }

    @Override
    public Person[] newArray(int size) {
      // TODO Auto-generated method stub
      return new Person[size];
    }
  };

  /**
   * Describe the kinds of special objects contained in this Parcelable's
   * marshalled(排列) representation(表現).
   * 
   * 用來描述序列化對象中特殊對象的分布狀況。
   * 
   * Returns a bitmask indicating the set of special object types marshalled
   * by the Parcelable.
   * 
   * @see android.os.Parcelable#describeContents()
   */

  @Override
  public int describeContents() {
    // TODO Auto-generated method stub
    return 0;
  }

  /**
   * 用來将對象轉換成 parcel 對象
   * 
   * 決定了把什麼資料寫入 parcel
   * 
   * @see android.os.Parcelable#writeToParcel(android.os.Parcel, int)
   */
  // 把 Person 對象轉化為 Parcel 對象存儲起來
  @Override
  public void <strong><span style="color:#ff0000;">writeToParcel</span></strong>(Parcel arg0, int arg1) {
    // TODO Auto-generated method stub

    arg0.writeInt(ID);
    arg0.writeString(Name);
    arg0.writeInt(age);
  }
}      

MainActivity.java

package com.serializabletest;

import java.io.IOException;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.View;

public class MainActivity extends Activity {

  public static final String TAG = "MainActivity";
  /** 序列化測試
   * @see android.app.Activity#onCreate(android.os.Bundle)
   */
  private final String objName = "/mnt/sdcard/object.txt";

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setTitle("Intent 傳遞對象");
    setContentView(R.layout.activity_main);

  }

  public void onBtnClick(View view) throws IOException {
    Person person = new Person(1, "張三", 26);

    Bundle bundle = new Bundle();
    bundle.putParcelable("person", person);
    Intent intent = new Intent(MainActivity.this, SecondActivity.class);
    intent.putExtras(bundle);
    startActivity(intent);
  }
}      

SecondActivity.java

package com.serializabletest;

import java.io.IOException;
import java.io.StreamCorruptedException;

import android.os.Bundle;
import android.view.View;
import android.app.Activity;
import android.content.Intent;

public class SecondActivity extends Activity {

  public static final String TAG = "MainActivity";
  /** 序列化測試
   * @see android.app.Activity#onCreate(android.os.Bundle)
   */
  private final String objName = "/mnt/sdcard/object.txt";

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setTitle("Intent 傳遞對象");
    setContentView(R.layout.activity_second);

    Intent intent = getIntent();
    Bundle bundle = intent.getExtras();
    Person person = bundle.getParcelable("person");
    person.printPerson();
  }

  public void onBtnClick(View view) throws StreamCorruptedException,
      IOException, ClassNotFoundException {
    this.finish();
  }

}