在TabletStatusBar.java的start()函数中有这样关于USB的状态监听机制
// storage
mStorageManager (StorageManager) context.getSystemService(Context.STORAGE_SERVICE);
mStorageManager.registerListener(
new com.android.systemui.usb.StorageNotification(context));
进入StorageManager.java的registerListener去查看是怎样监听的
public void registerListener(StorageEventListener listener) {
if (listener null) {
return;
}
synchronized (mListeners) {
mListeners.add(new ListenerDelegate(listener));
}
}
可见所谓注册过程就是将监听类添加到监听的List表中那么在这个表中如何监听的
查看ListenerDelegate
ListenerDelegate(StorageEventListener listener) {
mStorageEventListener listener;
mHandler new Handler(mTgtLooper) {
Override
public void handleMessage(Message msg) {
StorageEvent e (StorageEvent) msg.obj;
if (msg.what StorageEvent.EVENT_UMS_CONNECTION_CHANGED) {
UmsConnectionChangedStorageEvent ev (UmsConnectionChangedStorageEvent) e;
mStorageEventListener.onUsbMassStorageConnectionChanged(ev.available);
} else if (msg.what StorageEvent.EVENT_STORAGE_STATE_CHANGED) {
StorageStateChangedStorageEvent ev (StorageStateChangedStorageEvent) e;
mStorageEventListener.onStorageStateChanged(ev.path, ev.oldState, ev.newState);
} else {
Log.e(TAG, "Unsupported event " msg.what);
}
}
};
}
实际上就是开启一个无线循环的Handler等待消息的传送过来到这一步自然就会想到是谁发送消息
先插卡StorageManager类的构造函数
public StorageManager(Looper tgtLooper) throws RemoteException {
mMountService IMountService.Stub.asInterface(ServiceManager.getService("mount"));
if (mMountService null) {
Log.e(TAG, "Unable to connect to mount service! - is it running yet?");
return;
}
mTgtLooper tgtLooper;
mBinderListener new MountServiceBinderListener();
mMountService.registerListener(mBinderListener);
}
在开启StorageManager的时候实际上就开启一个MountService将MountServiceBinderListener注册为监听类
它的作用是这样的
private class MountServiceBinderListener extends IMountServiceListener.Stub {
public void onUsbMassStorageConnectionChanged(boolean available) {
final int size mListeners.size();
for (int i 0; i
mListeners.get(i).sendShareAvailabilityChanged(available);
}
}
public void onStorageStateChanged(String path, String oldState, String newState) {
final int size mListeners.size();
for (int i 0; i
mListeners.get(i).sendStorageStateChanged(path, oldState, newState);
}
}
}
也就是实际发送StorageEvent.EVENT_UMS_CONNECTION_CHANGED或者另外的消息
EVENT_STORAGE_STATE_CHANGED。
那么这个监听类如何知道状态变化的
在MountService.java中
public void registerListener(IMountServiceListener listener) {
synchronized (mListeners) {
MountServiceBinderListener bl new MountServiceBinderListener(listener);
try {
listener.asBinder().linkToDeath(bl, 0);
mListeners.add(bl);
} catch (RemoteException rex) {
Slog.e(TAG, "Failed to link to listener death");
}
}
}
在MountService中有一个可供守护进程调用的函数
public boolean onEvent(int code, String raw, String[] cooked)它在有关状态发生变化时会调用相关函数比如VolumeStateChange时notifyShareAvailabilityChange()而在notifyShareAvailabilityChange()中会更新
updatePublicVolumeState()在这里我们看到实际就是通过Environment中相关函数判断Sd卡状态
在这里
synchronized (mListeners) {
for (int i mListeners.size() -1; i > 0; i--) {
MountServiceBinderListener bl mListeners.get(i);
try {
bl.mListener.onStorageStateChanged(path, oldState, state);
} catch (RemoteException rex) {
Slog.e(TAG, "Listener dead");
mListeners.remove(i);
} catch (Exception ex) {
Slog.e(TAG, "Listener failed", ex);
}
}
}
也就是守护进程检测sd卡状态变化时调用StorageManager中的mBinderListener对象的onStorageStateChanged此时在StorageManager中就依次向需要知道Storage状态变化的目标发送消息刚才我们说的StorageManager开启的无限循环的Handler收到消息就开始了相应处理。
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