学步园

“USB连接方式”设置界面

选择MTP，PTP，UMS的选项界面就定义在UsbSettings.java，选择其中一个选项时会执行以下代码。

packages/apps/Settings/src/com/android/settings/deviceinfo/UsbSettings.java

        if (preference == mMtp) {          
            mUsbManager.setCurrentFunction(UsbManager.USB_FUNCTION_MTP, true);
            updateToggles(UsbManager.USB_FUNCTION_MTP);
        } else if (preference == mPtp) {   
            mUsbManager.setCurrentFunction(UsbManager.USB_FUNCTION_PTP, true);
            updateToggles(UsbManager.USB_FUNCTION_PTP);
        } else if(preference == mUms) {    
            mUsbManager.setCurrentFunction(UsbManager.USB_FUNCTION_MASS_STORAGE, true);
            updateToggles(UsbManager.USB_FUNCTION_MASS_STORAGE);
        }

updateToggle就是去让执行某些选项的选中与取消工作。

其中最重要的是mUsbManager.setCurrentFunction()，mUsbManger是这样得到的：

    @Override
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        mUsbManager = (UsbManager)getSystemService(Context.USB_SERVICE);
    }   

它的实现在frameworks/base/core/java/android/hardware/usb/UsbManager.java。

它的接口实现在frameworks/base/core/java/android/hardware/usb/IUsbManager.aidl

frameworks/base/services/java/com/android/server/usb/UsbService.java

/**    
 * UsbService manages all USB related state, including both host and device support.
 * Host related events and calls are delegated to UsbHostManager, and device related
 * support is delegated to UsbDeviceManager.
 */    
public class UsbService extends IUsbManager.Stub {
    private final Context mContext;
    private UsbDeviceManager mDeviceManager;
    private UsbHostManager mHostManager;
    private final UsbSettingsManager mSettingsManager;

这个界面就是"com.android.settings.UsbSettings" Activity。在frameworks/base/services/java/com/android/server/usb/UsbDeviceManager.java中被调用。

如果你选择了USB调试功能，还会弹出"com.android.settings.DevelopmentSettings" Activity，也是在UsbDeviceManager.java中被调用。关于UsbDevcieManager，我们以后再细看。

如果你选择了UMS，还会弹出"com.android.systemui.usb.UsbStorageActivity" Activity，就是“打开USB存储设备”的界面。它就义在定义在：
frameworks/base/packages/SystemUI/src/com/android/systemui/usb/UsbStorageActivity.java。

这些界面只有在插入USB时才会有通知显示。在没有插USB的情况下，有些界面是没有入口的。我们就以UsbStorageActivity为例，介绍一下这些通知是怎么弹出来的。

通知是怎么弹出来的

frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/phone/PhoneStatusBarPolicy.java

        // storage
        mStorageManager = (StorageManager) context.getSystemService(Context.STORAGE_SERVICE);
        mStorageManager.registerListener(
                new com.android.systemui.usb.StorageNotification(context));

这里注册了监听函数com.android.systemui.usb.StorageNotification，这个只是针对Phone，对于平板，有tablet/TabletStatusBarPolicy.java

我们来看一下注册的com.android.systemui.usb.StorageNotification

frameworks/base/packages/SystemUI/src/com/android/systemui/usb/StorageNotification.java

public class StorageNotification extends StorageEventListener { 
    private static final String TAG = "StorageNotification";

    public StorageNotification(Context context) {
        mContext = context;

        mStorageManager = (StorageManager) context.getSystemService(Context.STORAGE_SERVICE);
        final boolean connected = mStorageManager.isUsbMassStorageConnected();
        Slog.d(TAG, String.format( "Startup with UMS connection %s (media state %s)", mUmsAvailable,
                Environment.getExternalStorageState()));
        
        HandlerThread thr = new HandlerThread("SystemUI StorageNotification");
        thr.start();
        mAsyncEventHandler = new Handler(thr.getLooper());

        onUsbMassStorageConnectionChanged(connected);
    }

在构造函数里就调用了onUsbMassStorageConnectionChanged函数，它最终会调到updateUsbMassStorageNotification()，

    /** 
     * Update the state of the USB mass storage notification
     */
    void updateUsbMassStorageNotification(boolean available) {

        if (available) {
            Intent intent = new Intent();
            intent.setClass(mContext, com.android.systemui.usb.UsbStorageActivity.class);
            intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);

            PendingIntent pi = PendingIntent.getActivity(mContext, 0, intent, 0); 
            setUsbStorageNotification(
                    com.android.internal.R.string.usb_storage_notification_title,
                    com.android.internal.R.string.usb_storage_notification_message,
                    com.android.internal.R.drawable.stat_sys_data_usb,
                    false, true, pi);
        } else {
            setUsbStorageNotification(0, 0, 0, false, false, null);
        }   
    }   

也就是说UsbStorageActivity和StorageNotification绑定在了一起，什么时候弹出这个通知，就可以进入这个Activity了。

如果连接了USB，就会在通知栏里显示USB选项的通知。如果没有连接，就会把这个通知给取消掉。那我们看一下，这个通知是怎么弹出来的。

StorageManager

frameworks/base/core/java/android/os/storage/StorageManager.java

    public void registerListener(StorageEventListener listener) {
        if (listener == null) {            
            return;
        }

        synchronized (mListeners) {        
            mListeners.add(new ListenerDelegate(listener));
        }
    }  

mListeners会被私有成员MountServiceBinderListener用到，而MountServiceBinderListener又是继承自IMountServiceListener.Stub，在构造函数里被注册。

    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);
    }

所以关键还是在mMountService。