Android Parcel学习

Parcel是一个轻量级的对象序列化，（类似Serierlizable）， 可用于进程间通信，用的时候需要写个static CREATOR， 写入数据和读出的顺序必需一致。

这里是 一个Stackoverflow上的例子

研究了下怎么样传送List<T>， 下面这个例子直接传ArrayList<String>:

public class MyParcelInfo implements Parcelable {
	private int feildCount;
	private ArrayList<String> feildNameList;
	
	public MyParcelInfo(Parcel in) {
		feildCount = in.readInt();
		feildNameList = new ArrayList<String>();
		in.readList(feildNameList, ClassLoader.getSystemClassLoader());
	}

	public MyParcelInfo() {
	}

	public int describeContents() {
		return 0;
	}

	public void writeToParcel(Parcel dest, int flags) {
		dest.writeInt(feildCount);
		dest.writeList(feildNameList);

	}

	public static final Parcelable.Creator<MyParcelInfo> CREATOR = new Parcelable.Creator<MyParcelInfo>() {
		public MyParcelInfo createFromParcel(Parcel in) {
			return new MyParcelInfo(in);
		}

		public MyParcelInfo[] newArray(int size) {
			return new MyParcelInfo[size];
		}
	};
	
	public void setFeildCount(int count) {
		this.feildCount = count;
	}

	public int getFeildCount() {
		return this.feildCount;
	}
	
	public ArrayList<String> getFeildList() {
		return this.feildNameList;
	}
	
	public void setFeildList(ArrayList<String> list){
		this.feildNameList = list;
	}
}

下面是发送代码：
protected void sendParcel() {
		
		MyParcelInfo info = new MyParcelInfo();
		
		info.setFeildCount(4);
		
		ArrayList<String> list = new ArrayList<String>();
		list.add("Lisp");
		list.add("JNI");
		list.add("Net");
		list.add("Box2d");
		info.setFeildList(list);
		
		Intent it = new Intent(MainActivity.this, ParcelReceiverActivity.class);
		it.putExtra("info", info);
		this.startActivity(it);
	}

下面是接收代码：

MyParcelInfo info = this.getIntent().getParcelableExtra("info");
		ArrayList<String> infoList = info.getFeildList();

和String一样，如下的类型可以传送：

• null
• String
• Byte
• Short
• Integer
• Long
• Float
• Double
• Boolean
• String[]
• boolean[]
• byte[]
• int[]
• long[]
• Object[] (supporting objects of the same type defined here).
• Bundle
• Map (as supported by writeMap).
• Any object that implements the Parcelable protocol.
• Parcelable[]
• CharSequence (as supported by TextUtils.writeToParcel).
• List (as supported by writeList).
• SparseArray (as supported by writeSparseArray).
• IBinder
• Any object that implements Serializable (but see writeSerializable for caveats). Note that all of the previous types have relatively efficient implementations for writing to a Parcel; having to rely on the generic serialization approach is much less efficient and should be avoided whenever possible.

注意如果要传送其它自定义类型的对象，这个对象必须要implements Parcelable.

parcel可以用于Activity之间传送对象，相比于用Bundle传送，Parcel的好处是可以把数据打包成对象传送，可读性和可维性比用Bundle传一大堆Key,Value键值对要好，同时也可以扩展为传递其它类型的对象(implements Serializalbe or Parcelable).

关于进程间通信的应用，有待进一步研究。