Android RemoteCallbackList类
在网上很少看到有解释 RemoteCallbackList类的，没办法要搞懂只能去看源码，大致理解：一个容器，容纳的对象是一些接口，用于执行列表中对象的回调函数，主要用于服务调用activity函数，或者解释为服务端和客户端通信。
/*
* Copyright (C) 2008 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.os;
import java.util.HashMap;
/**
* Takes care of the grunt work of maintaining a list of remote interfaces,
* typically for the use of performing callbacks from a
* {@link android.app.Service} to its clients. In particular, this:
*
*
* - Keeps track of a set of registered {@link IInterface} callbacks,
* taking care to identify them through their underlying unique {@link IBinder}
* (by calling {@link IInterface#asBinder IInterface.asBinder()}.
*
- Attaches a {@link IBinder.DeathRecipient IBinder.DeathRecipient} to
* each registered interface, so that it can be cleaned out of the list if its
* process goes away.
*
- Performs locking of the underlying list of interfaces to deal with
* multithreaded incoming calls, and a thread-safe way to iterate over a
* snapshot of the list without holding its lock.
*
*
* To use this class, simply create a single instance along with your
* service, and call its {@link #register} and {@link #unregister} methods
* as client register and unregister with your service. To call back on to
* the registered clients, use {@link #beginBroadcast},
* {@link #getBroadcastItem}, and {@link #finishBroadcast}.
*
*
If a registered callback's process goes away, this class will take
* care of automatically removing it from the list. If you want to do
* additional work in this situation, you can create a subclass that
* implements the {@link #onCallbackDied} method.
*/
public class RemoteCallbackList<E extends IInterface> {
/*package*/ HashMap mCallbacks
= new HashMap();
private Object[] mActiveBroadcast;
private int mBroadcastCount = -1;
private boolean mKilled = false;
private final class Callback implements IBinder.DeathRecipient {
final E mCallback;
final Object mCookie;
Callback(E callback, Object cookie) {
mCallback = callback;
mCookie = cookie;
}
public void binderDied() {
synchronized (mCallbacks) {
mCallbacks.remove(mCallback.asBinder());
}
onCallbackDied(mCallback, mCookie);
}
}
/**
* Simple version of {@link RemoteCallbackList#register(E, Object)}
* that does not take a cookie object.
*/
public boolean register(E callback) {
return register(callback, null);
}
/**
* Add a new callback to the list. This callback will remain in the list
* until a corresponding call to {@link #unregister} or its hosting process
* goes away. If the callback was already registered (determined by
* checking to see if the {@link IInterface#asBinder callback.asBinder()}
* object is already in the list), then it will be left as-is.
* Registrations are not counted; a single call to {@link #unregister}
* will remove a callback after any number calls to register it.
*
* @param callback The callback interface to be added to the list. Must
* not be null -- passing null here will cause a NullPointerException.
* Most services will want to check for null before calling this with
* an object given from a client, so that clients can't crash the
* service with bad data.
*
* @param cookie Optional additional data to be associated with this
* callback.
*
* @return Returns true if the callback was successfully added to the list.
* Returns false if it was not added, either because {@link #kill} had
* previously been called or the callback's process has gone away.
*
* @see #unregister
* @see #kill
* @see #onCallbackDied
*/
public boolean register(E callback, Object cookie) {
synchronized (mCallbacks) {
if (mKilled) {
return false;
}
IBinder binder = callback.asBinder();
try {
Callback cb = new Callback(callback, cookie);
binder.linkToDeath(cb, 0);
mCallbacks.put(binder, cb);
return true;
} catch (RemoteException e) {
return false;
}
}
}
/**
* Remove from the list a callback that was previously added with
* {@link #register}. This uses the
* {@link IInterface#asBinder callback.asBinder()} object to correctly
* find the previous registration.
* Registrations are not counted; a single unregister call will remove
* a callback after any number calls to {@link #register} for it.
*
* @param callback The callback to be removed from the list. Passing
* null here will cause a NullPointerException, so you will generally want
* to check for null before calling.
*
* @return Returns true if the callback was found and unregistered. Returns
* false if the given callback was not found on the list.
*
* @see #register
*/
public boolean unregister(E callback) {
synchronized (mCallbacks) {
Callback cb = mCallbacks.remove(callback.asBinder());
if (cb != null) {
cb.mCallback.asBinder().unlinkToDeath(cb, 0);
return true;
}
return false;
}
}
/**
* Disable this callback list. All registered callbacks are unregistered,
* and the list is disabled so that future calls to {@link #register} will
* fail. This should be used when a Service is stopping, to prevent clients
* from registering callbacks after it is stopped.
*
* @see #register
*/
public void kill() {
synchronized (mCallbacks) {
for (Callback cb : mCallbacks.values()) {
cb.mCallback.asBinder().unlinkToDeath(cb, 0);
}
mCallbacks.clear();
mKilled = true;
}
}
/**
* Old version of {@link #onCallbackDied(E, Object)} that
* does not provide a cookie.
*/
public void onCallbackDied(E callback) {
}
/**
* Called when the process hosting a callback in the list has gone away.
* The default implementation calls {@link #onCallbackDied(E)}
* for backwards compatibility.
*
* @param callback The callback whose process has died. Note that, since
* its process has died, you can not make any calls on to this interface.
* You can, however, retrieve its IBinder and compare it with another
* IBinder to see if it is the same object.
* @param cookie The cookie object original provided to
* {@link #register(E, Object)}.
*
* @see #register
*/
public void onCallbackDied(E callback, Object cookie) {
onCallbackDied(callback);
}
/**
* Prepare to start making calls to the currently registered callbacks.
* This creates a copy of the callback list, which you can retrieve items
* from using {@link #getBroadcastItem}. Note that only one broadcast can
* be active at a time, so you must be sure to always call this from the
* same thread (usually by scheduling with {@link Handler}) or
* do your own synchronization. You must call {@link #finishBroadcast}
* when done.
*
* A typical loop delivering a broadcast looks like this:
*
*
* int i = callbacks.beginBroadcast();
* while (i > 0) {
* i--;
* try {
* callbacks.getBroadcastItem(i).somethingHappened();
* } catch (RemoteException e) {
* // The RemoteCallbackList will take care of removing
* // the dead object for us.
* }
* }
* callbacks.finishBroadcast();
*
* @return Returns the number of callbacks in the broadcast, to be used
* with {@link #getBroadcastItem} to determine the range of indices you
* can supply.
*
* @see #getBroadcastItem
* @see #finishBroadcast
*/
public int beginBroadcast() {
synchronized (mCallbacks) {
if (mBroadcastCount > 0) {
throw new IllegalStateException(
"beginBroadcast() called while already in a broadcast");
}
final int N = mBroadcastCount = mCallbacks.size();
if (N <= 0) {
return 0;
}
Object[] active = mActiveBroadcast;
if (active == null || active.length < N) {
mActiveBroadcast = active = new Object[N];
}
int i=0;
for (Callback cb : mCallbacks.values()) {
active[i++] = cb;
}
return i;
}
}
/**
* Retrieve an item in the active broadcast that was previously started
* with {@link #beginBroadcast}. This can only be called after
* the broadcast is started, and its data is no longer valid after
* calling {@link #finishBroadcast}.
*
* Note that it is possible for the process of one of the returned
* callbacks to go away before you call it, so you will need to catch
* {@link RemoteException} when calling on to the returned object.
* The callback list itself, however, will take care of unregistering
* these objects once it detects that it is no longer valid, so you can
* handle such an exception by simply ignoring it.
*
* @param index Which of the registered callbacks you would like to
* retrieve. Ranges from 0 to 1-{@link #beginBroadcast}.
*
* @return Returns the callback interface that you can call. This will
* always be non-null.
*
* @see #beginBroadcast
*/
public E getBroadcastItem(int index) {
return ((Callback)mActiveBroadcast[index]).mCallback;
}
/**
* Retrieve the cookie associated with the item
* returned by {@link #getBroadcastItem(int)}.
*
* @see #getBroadcastItem
*/
public Object getBroadcastCookie(int index) {
return ((Callback)mActiveBroadcast[index]).mCookie;
}
/**
* Clean up the state of a broadcast previously initiated by calling
* {@link #beginBroadcast}. This must always be called when you are done
* with a broadcast.
*
* @see #beginBroadcast
*/
public void finishBroadcast() {
if (mBroadcastCount < 0) {
throw new IllegalStateException(
"finishBroadcast() called outside of a broadcast");
}
Object[] active = mActiveBroadcast;
if (active != null) {
final int N = mBroadcastCount;
for (int i=0; inull;
}
}
mBroadcastCount = -1;
}
/**
* Returns the number of registered callbacks. Note that the number of registered
* callbacks may differ from the value returned by {@link #beginBroadcast()} since
* the former returns the number of callbacks registered at the time of the call
* and the second the number of callback to which the broadcast will be delivered.
*
* This function is useful to decide whether to schedule a broadcast if this
* requires doing some work which otherwise would not be performed.
*
*
* @return The size.
*/
public int getRegisteredCallbackCount() {
synchronized (mCallbacks) {
if (mKilled) {
return 0;
}
return mCallbacks.size();
}
}
}
通过查看上面的源码，我们可以知道主要是维护 mCallbacks ，mCallbacks中包含我们的客户端接口
/*package*/ HashMap mCallbacks
= new HashMap(); 其中常用的几个函数 register
public boolean register(E callback) {
return register(callback, null);
}
public boolean register(E callback, Object cookie) {
synchronized (mCallbacks) {
if (mKilled) {
return false;
}
IBinder binder = callback.asBinder();
try {
Callback cb = new Callback(callback, cookie);
binder.linkToDeath(cb, 0);
mCallbacks.put(binder, cb);
return true;
} catch (RemoteException e) {
return false;
}
}
}
向 mCallbacks中添加接口对象，主要使用 mCallbacks.put(binder, cb);方法，
unregister()方法
public boolean unregister(E callback) {
synchronized (mCallbacks) {
Callback cb = mCallbacks.remove(callback.asBinder());
if (cb != null) {
cb.mCallback.asBinder().unlinkToDeath(cb, 0);
return true;
}
return false;
}
}通过 mCallbacks.remove(callback.asBinder()); 从HashMap中删除
kill()方法
public void kill() {
synchronized (mCallbacks) {
for (Callback cb : mCallbacks.values()) {
cb.mCallback.asBinder().unlinkToDeath(cb, 0);
}
mCallbacks.clear();
mKilled = true;
}
}通过 mCallbacks.clear(); 清空集合。
beginBroadcast() ;
public int beginBroadcast() {
synchronized (mCallbacks) {
if (mBroadcastCount > 0) {
throw new IllegalStateException(
"beginBroadcast() called while already in a broadcast");
}
final int N = mBroadcastCount = mCallbacks.size();
if (N <= 0) {
return 0;
}
Object[] active = mActiveBroadcast;
if (active == null || active.length < N) {
mActiveBroadcast = active = new Object[N];
}
int i=0;
for (Callback cb : mCallbacks.values()) {
active[i++] = cb;
}
return i;
}
}从注释的解释来说大致是：准备开始调用当前注册的回调。这将创建一个回调列表的副本,你可以从使用getBroadcastItem检索条目，注意:一次只能激活一个广播,所以你必须确保总是从同一个线程调用这个或者是自己做同步。完成后必须调用finishBroadcast。
返回值：callbacks的大小；
如果 mBroadcastCount > 0 说明之前调用过beginBroadcast()，则会抛出异常；
getBroadcastItem()方法 从副本中获取我们之前存入的接口对象
public E getBroadcastItem(int index) {
return ((Callback)mActiveBroadcast[index]).mCallback;
}finishBroadcast()，清理我们之前建立的active[] 副本
public void finishBroadcast() {
if (mBroadcastCount < 0) {
throw new IllegalStateException(
"finishBroadcast() called outside of a broadcast");
}
Object[] active = mActiveBroadcast;
if (active != null) {
final int N = mBroadcastCount;
for (int i=0; inull;
}
}
mBroadcastCount = -1;
} 如果 mBroadcastCount <0 说明之前掉用过finishBroadcast() 则会抛出异常。
常用的函数大概就是这个样子，如果我理解有误欢迎大家留言指正，也欢迎大家补充，一起学习