Parcelable

阅读Android源代码时，经常看到使用Parcelable的地方，但是一直没太搞清楚它的作用，今天仔细的看了一下，感觉就是把一堆数据打包，然后传输，然后再分解出来。

public interface Parcelable,如果某个类实现了这个接口，那么它的对象实例可以写入到Parcel中，并且能够从中恢复，并且这个类必须要有一个static的field，并且名称要为CREATOR，这个field是某个实现了Parcelable.Creator接口的类的对象实例。

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();     } }

public static 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
其有两个成员函数：createFromParcel和newArray。
createFromParcel函数创建实现Parcelable接口的某个类的一个新的对象实例，并且用从给定的Parcel中获取的数据进行实例化，Parcel中的数据是在之前通过Parcelable.writeToParcel方式写入的数据。
newArray函数创建实现Parcelable接口的某个类的一个新的对象数组，数组中的每个项都被初始化为null。
编写了一个简单的程序进行了测试，就是从一个Activity向另外一个Activity传递数据：

PersonMsg.java

package com.example.parcelable;import android.os.Parcel;import android.os.Parcelable;public class PersonMsg implements Parcelable{ private String name = null; private int age = 0;  public String getName() {  return name; } public void setName(String name) {  this.name = name; } public int getAge()  {  return age; } public void setAge(int age) {  this.age = age; } public int describeContents()  {   return 0; }  public void writeToParcel(Parcel out, int flags)  {  out.writeString(name);  out.writeInt(age); }  public static final Parcelable.Creator<PersonMsg> CREATOR =   new Parcelable.Creator<PersonMsg>()  {    public PersonMsg createFromParcel(Parcel in)    {    PersonMsg msg = new PersonMsg();    msg.name = in.readString();    msg.age = in.readInt();     return msg;   }   public PersonMsg[] newArray(int size)    {     return new PersonMsg[size];   }  };}

ActivityFrom.java

package com.example.parcelable;import android.app.Activity;import android.content.Intent;import android.os.Bundle;import android.util.Log;import android.view.View;import android.widget.Button;import android.widget.EditText;public class ActivityFrom extends Activity { private EditText nameEditText = null; private EditText ageEditText = null; private Button startButton = null;     /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState)     {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);                nameEditText = (EditText)findViewById(R.id.name_content);        ageEditText = (EditText)findViewById(R.id.age_content);        startButton = (Button)findViewById(R.id.start);                startButton.setOnClickListener(new View.OnClickListener()        {   public void onClick(View v)    {    String name = nameEditText.getEditableText().toString();    int age = Integer.valueOf(ageEditText.getEditableText().toString());        Log.d("name is: ", name);    Log.d("age is: ", age + "");        PersonMsg msg = new PersonMsg();    msg.setName(name);    msg.setAge(age);        Intent intent = new Intent();    intent.setClass(ActivityFrom.this, ActivityTo.class);    intent.putExtra("personmsg", msg);    startActivity(intent);   }  });    }}

ActivityTo.java

package com.example.parcelable;import android.app.Activity;import android.content.Intent;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.EditText;public class ActivityTo extends Activity{ private EditText nameEditText = null; private EditText ageEditText = null; private Button startButton = null;     /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState)     {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);                nameEditText = (EditText)findViewById(R.id.name_content);        ageEditText = (EditText)findViewById(R.id.age_content);        startButton = (Button)findViewById(R.id.start);        startButton.setVisibility(View.INVISIBLE);                Intent intent = getIntent();        PersonMsg msg = (PersonMsg)intent.getParcelableExtra("personmsg");        String name = msg.getName();        int age = msg.getAge();                nameEditText.setText(name);        ageEditText.setText(age + "");    }}

main.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="vertical"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    > <LinearLayout  android:id="@+id/first_row"  android:layout_width="fill_parent"  android:layout_height="50dip"  android:orientation="horizontal"  >  <TextView   android:id="@+id/name_label"   android:layout_width="60dip"   android:layout_height="fill_parent"   android:gravity="center"   android:text="Name"   >  </TextView>  <EditText   android:id="@+id/name_content"   android:layout_width="fill_parent"   android:layout_height="fill_parent"   android:gravity="center_vertical|left"   >  </EditText> </LinearLayout> <LinearLayout  android:id="@+id/second_row"  android:layout_width="fill_parent"  android:layout_height="50dip"  android:orientation="horizontal"  >  <TextView   android:id="@+id/age_label"   android:layout_width="60dip"   android:layout_height="fill_parent"   android:gravity="center"   android:text="Age"   >  </TextView>  <EditText   android:id="@+id/age_content"   android:layout_width="fill_parent"   android:layout_height="fill_parent"   android:gravity="center_vertical|left"   >  </EditText> </LinearLayout> <Button  android:id="@+id/start"  android:layout_width="fill_parent"  android:layout_height="50dip"  android:gravity="center"  android:text="start"  > </Button></LinearLayout>

实验结果:

点击开始: