Android:Intent传递数据的几种类型和源码实现

public class Intent implements Parcelable, Cloneable {   //... private String mAction;
private Uri mData;
private String mType;
private String mPackage;
private ComponentName mComponent;
private int mFlags;
private HashSet<String> mCategories;
private Bundle mExtras;
private Rect mSourceBounds;

Intent也是继承了Parcelable的接口。

个人理解，Intent应该只是一个数据参数的载体，真正将两个Acitivity/Service通信起来的是Binder接口(C/S架构)。

第一类:简单或基本数据类型

Intent putExtra(String name, int[] value)
Intent putExtra(String name, float value)
Intent putExtra(String name, byte[] value)
Intent putExtra(String name, long[] value)
Intent putExtra(String name, float[] value)
Intent putExtra(String name, long value)
Intent putExtra(String name, String[] value)
Intent putExtra(String name, boolean value)
Intent putExtra(String name, boolean[] value)
Intent putExtra(String name, short value)
Intent putExtra(String name, double value)
Intent putExtra(String name, short[] value)
Intent putExtra(String name, String value)
Intent putExtra(String name, byte value)
Intent putExtra(String name, char[] value)
Intent putExtra(String name, CharSequence[] value)

本质上仍然是通过一个Bundle(private Bundle mExtras;)来实现：

public Intent putExtra(String name, long value) {
if (mExtras == null) {
mExtras = new Bundle();
}
mExtras.putLong(name, value);
return this;
}

第二类:传递一个Bundle

public Intent putExtra(String name, Bundle value) {
if (mExtras == null) {
mExtras = new Bundle();
}
mExtras.putBundle(name, value);
return this;
}

第三类：传递Serializable对象

public Intent putExtra(String name, Serializable value) {
if (mExtras == null) {
mExtras = new Bundle();
}
mExtras.putSerializable(name, value);
return this;
}

第四类：Parcelable对象

public Intent putExtra(String name, Parcelable value) {
if (mExtras == null) {
mExtras = new Bundle();
}
mExtras.putParcelable(name, value);
return this;
}
public Intent putExtra(String name, Parcelable[] value) {
if (mExtras == null) {
mExtras = new Bundle();
}
mExtras.putParcelableArray(name, value);
return this;
}

第五类：Intent

public Intent putExtras(Intent src) {
if (src.mExtras != null) {
if (mExtras == null) {
mExtras = new Bundle(src.mExtras);
} else {
mExtras.putAll(src.mExtras);
}
}
return this;
}

归根结底都是通过Bundle来实现数据封装。而Bundle则是通过Map的数据结构来存储数据。

mMap = new HashMap<String, Object>();

mParcelledData

两者同时只有一个有效。

一旦unparcel以后，mParcelledData

的数据将被填充到mMap中，同时值为null。在writeToParcel和readFromParcel中则直接使用mParcelledData.此时一般通过IBinder关联两个进程的通信。

关于Bundle则是实现了Parcelable接口的类，通过上面提到的HashMap和一个Parcel来存储数据。

public final class Bundle implements Parcelable, Cloneable {
private static final String LOG_TAG = "Bundle";
public static final Bundle EMPTY;

static {
EMPTY = new Bundle();
EMPTY.mMap = Collections.unmodifiableMap(new HashMap<String, Object>());
}

// Invariant - exactly one of mMap / mParcelledData will be null
// (except inside a call to unparcel)

/* package */ Map<String, Object> mMap = null;

/*
* If mParcelledData is non-null, then mMap will be null and the
* data are stored as a Parcel containing a Bundle.  When the data
* are unparcelled, mParcelledData willbe set to null.
*/
/* package */ Parcel mParcelledData = null;

public void putFloat(String key, float value) {
unparcel();//首先解析出mParcelledData到mMap
mMap.put(key, value);
}

/* package */ synchronized void unparcel() {
if (mParcelledData == null) {
return;
}

int N = mParcelledData.readInt();
if (N < 0) {
return;
}
if (mMap == null) {
mMap = new HashMap<String, Object>();
}
mParcelledData.readMapInternal(mMap, N, mClassLoader);
mParcelledData.recycle();
mParcelledData = null;//回收以后值为null
}