frameworks/base/core/java/android/os/Parce.java
Parcel: Container for a message
/**
* Container for a message (data and object references) that can
* be sent through an IBinder. A Parcel can contain both flattened data
* that will be unflattened on the other side of the IPC (using the various
* methods here for writing specific types, or the general
* Parcelable interface), and references to live {IBinder}
* objects that will result in the other side receiving a proxy IBinder
* connected with the original IBinder in the Parcel.
*
* Parcel is not a general-purpose
* serialization mechanism. This class (and the corresponding
* {Parcelable} API for placing arbitrary objects into a Parcel) is
* designed as a high-performance IPC transport. As such, it is not
* appropriate to place any Parcel data in to persistent storage: changes
* in the underlying implementation of any of the data in the Parcel can
* render older data unreadable.
*
* The bulk of the Parcel API revolves around reading and writing data
* of various types. There are six major classes of such functions available.
*
* 1] Primitives
* The most basic data functions are for writing and reading primitive
* data types: {@link #writeByte}, {@link #readByte}, {@link #writeDouble},
* {@link #readDouble}, {@link #writeFloat}, {@link #readFloat}, {@link #writeInt},
* {@link #readInt}, {@link #writeLong}, {@link #readLong},
* {@link #writeString}, {@link #readString}. Most other
* data operations are built on top of these. The given data is written and
* read using the endianess of the host CPU.</p>
*
* 2] Primitive Arrays
* There are a variety of methods for reading and writing raw arrays
* of primitive objects, which generally result in writing a 4-byte length
* followed by the primitive data items. The methods for reading can either
* read the data into an existing array, or create and return a new array.
* These available types are:
*
* <ul>
* <li> {@link #writeBooleanArray(boolean[])},
* {@link #readBooleanArray(boolean[])}, {@link #createBooleanArray()}
* <li> {@link #writeByteArray(byte[])},
* {@link #writeByteArray(byte[], int, int)}, {@link #readByteArray(byte[])},
* {@link #createByteArray()}
* <li> {@link #writeCharArray(char[])}, {@link #readCharArray(char[])},
* {@link #createCharArray()}
* <li> {@link #writeDoubleArray(double[])}, {@link #readDoubleArray(double[])},
* {@link #createDoubleArray()}
* <li> {@link #writeFloatArray(float[])}, {@link #readFloatArray(float[])},
* {@link #createFloatArray()}
* <li> {@link #writeIntArray(int[])}, {@link #readIntArray(int[])},
* {@link #createIntArray()}
* <li> {@link #writeLongArray(long[])}, {@link #readLongArray(long[])},
* {@link #createLongArray()}
* <li> {@link #writeStringArray(String[])}, {@link #readStringArray(String[])},
* {@link #createStringArray()}.
* <li> {@link #writeSparseBooleanArray(SparseBooleanArray)},
* {@link #readSparseBooleanArray()}.
* </ul>
*
* 3] Parcelables
*
* The {@link Parcelable} protocol provides an extremely efficient (but
* low-level) protocol for objects to write and read themselves from Parcels.
* You can use the direct methods {@link #writeParcelable(Parcelable, int)}
* and {@link #readParcelable(ClassLoader)} or
* {@link #writeParcelableArray} and
* {@link #readParcelableArray(ClassLoader)} to write or read. These
* methods write both the class type and its data to the Parcel, allowing
* that class to be reconstructed from the appropriate class loader when
* later reading.
*
* 4] Bundles
A mapping from String keys to various {@link Parcelable} values.
* A special type-safe container, called {Bundle}, is available
* for key/value maps of heterogeneous values. This has many optimizations
* for improved performance when reading and writing data, and its type-safe
* API avoids difficult to debug type errors when finally marshalling the
* data contents into a Parcel. The methods to use are
* {writeBundle(Bundle)}, {readBundle()}, and
* {readBundle(ClassLoader)}.
*
* 5] Active Objects
*
* An unusual feature of Parcel is the ability to read and write active
* objects. For these objects the actual contents of the object is not
* written, rather a special token referencing the object is written. When
* reading the object back from the Parcel, you do not get a new instance of
* the object, but rather a handle that operates on the exact same object that
* was originally written. There are two forms of active objects available.
*
* {Binder} objects are a core facility of Android's general cross-process
* communication system. The {IBinder} interface describes an abstract
* protocol with a Binder object. Any such interface can be written in to
* a Parcel, and upon reading you will receive either the original object
* implementing that interface or a special proxy implementation
* that communicates calls back to the original object. The methods to use are
* {@link #writeStrongBinder(IBinder)},
* {@link #writeStrongInterface(IInterface)}, {@link #readStrongBinder()},
* {@link #writeBinderArray(IBinder[])}, {@link #readBinderArray(IBinder[])},
* {@link #createBinderArray()},
* {@link #writeBinderList(List)}, {@link #readBinderList(List)},
* {@link #createBinderArrayList()}.</p>
*
* FileDescriptor objects, representing raw Linux file descriptor identifiers,
* can be written and {@link ParcelFileDescriptor} objects returned to operate
* on the original file descriptor. The returned file descriptor is a dup
* of the original file descriptor: the object and fd is different, but
* operating on the same underlying file stream, with the same position, etc.
* The methods to use are {@link #writeFileDescriptor(FileDescriptor)},
* {@link #readFileDescriptor()}.
* 6] Untyped Containers
* A final class of methods are for writing and reading standard Java
* containers of arbitrary types. These all revolve around the
* {@link #writeValue(Object)} and {@link #readValue(ClassLoader)} methods
* which define the types of objects allowed. The container methods are
* {@link #writeArray(Object[])}, {@link #readArray(ClassLoader)},
* {@link #writeList(List)}, {@link #readList(List, ClassLoader)},
* {@link #readArrayList(ClassLoader)},
* {@link #writeMap(Map)}, {@link #readMap(Map, ClassLoader)},
* {@link #writeSparseArray(SparseArray)},
* {@link #readSparseArray(ClassLoader)}.
*/
Parcel write/read 实现
primitive Integer
public final void writeInt(int val) {
nativeWriteInt(mNativePtr, val);
}
frameworks/base/core/jni/android_os_Parcel.cpp
static jlong android_os_Parcel_create(JNIEnv* env, jclass clazz)
{//jni层创建Parcel, 并返回到Parcel对象指针到java层: mNavtivePtr
Parcel* parcel = new Parcel();
return reinterpret_cast<jlong>(parcel);
}
static void android_os_Parcel_writeInt(JNIEnv* env, jclass clazz, jlong nativePtr, jint val) {
// java层传入的nativePtr:就是JNI层创建的Parcel对象指针
Parcel* parcel = reinterpret_cast<Parcel*>(nativePtr);
if (parcel != NULL) {
parcel->writeInt32(val);
}
}
WriteParcelable
/**
* Flatten the name of the class of the Parcelable and its contents
* into the parcel.
*
* @param p The Parcelable object to be written.
* @param parcelableFlags Contextual flags as per
* {@link Parcelable#writeToParcel(Parcel, int) Parcelable.writeToParcel()}.
*/
public final void writeParcelable(Parcelable p, int parcelableFlags) {
writeParcelableCreator(p);
p.writeToParcel(this, parcelableFlags);
}
/** @hide */
public final void writeParcelableCreator(Parcelable p) {
String name = p.getClass().getName();
writeString(name);
}
写Parcelable class name后，再调用派生的 writeToParcel.
Parcelable
/**
* Interface for classes whose instances can be written to
* and restored from a {@link Parcel}. Classes implementing the Parcelable
* interface must also have a non-null static field called <code>CREATOR</code>
* of a type that implements the {@link Parcelable.Creator} interface.
*
* A typical implementation of Parcelable is:
*
*
* public class MyParcelable implements Parcelable {
* private int mData;
*
* public int describeContents() {
* return 0;
* }
*
* public void writeToParcel(Parcel out, int flags) {
* out.writeInt(mData);//把成员变量写入Parcel
* }
*
* 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();//从Parcel中获得成员变量
* }
* }
*/