Android 6.0 MTP

最新推荐文章于 2024-02-20 00:15:00 发布

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最新推荐文章于 2024-02-20 00:15:00 发布

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分类专栏： Android 基础业务分析

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本文详细解析了MTP（Media Transfer Protocol）的工作流程和技术细节。从USB状态广播开始，介绍了如何通过MtpReceiver监听并响应USB状态变化，进一步启动MtpService进行MTP模式的开启与关闭操作。

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MTP主要处理逻辑

一、UsbDevicemanager发送usb状态广播

UsbDevicemanager发送ACTION_USB_STATE的广播，来通知usb状态的变化

private void updateUsbStateBroadcast() {  
    // send a sticky broadcast containing current USB state  
    boolean UsbDataUnlocked = isUsbTransferAllowed() && mUsbDataUnlocked ;  
    Intent intent = new Intent(UsbManager.ACTION_USB_STATE);  
    intent.addFlags(Intent.FLAG_RECEIVER_REPLACE_PENDING  
            | Intent.FLAG_RECEIVER_FOREGROUND);  
    intent.putExtra(UsbManager.USB_CONNECTED, mConnected);  
    intent.putExtra(UsbManager.USB_CONFIGURED, mConfigured);  
    intent.putExtra(UsbManager.USB_DATA_UNLOCKED, UsbDataUnlocked);  
  
    if (mCurrentFunctions != null) {  
        String[] functions = mCurrentFunctions.split(",");  
        for (int i = 0; i < functions.length; i++) {  
            intent.putExtra(functions[i], true);//这里是各个functions的状态  
        }  
    }  
  
    if (DEBUG) Slog.d(TAG, "broadcasting " + intent + " , connected: " + mConnected  
                            + " , configured: " + mConfigured + " , UsbDataUnlocked: " + UsbDataUnlocked  
                            + " , CurrentFunctions: " + mCurrentFunctions);  
    mContext.sendStickyBroadcastAsUser(intent, UserHandle.ALL);

MtpReceiver.java

这个属于应用的代码，先监听开机广播，然后注册ACTION_USB_STATE广播，最后在handleUsbState的时候会启动MtpService

   private void handleUsbState(Context context, Intent intent) {
        Bundle extras = intent.getExtras();
        boolean connected = extras.getBoolean(UsbManager.USB_CONFIGURED);
        boolean mtpEnabled = extras.getBoolean(UsbManager.USB_FUNCTION_MTP);
        boolean ptpEnabled = extras.getBoolean(UsbManager.USB_FUNCTION_PTP);
        boolean unlocked = extras.getBoolean(UsbManager.USB_DATA_UNLOCKED);
        // Start MTP service if USB is connected and either the MTP or PTP function is enabled
        if (connected && (mtpEnabled || ptpEnabled)) {
            intent = new Intent(context, MtpService.class);
            intent.putExtra(UsbManager.USB_DATA_UNLOCKED, unlocked);
            if (ptpEnabled) {
                intent.putExtra(UsbManager.USB_FUNCTION_PTP, true);
            }
            if (DEBUG) { Log.d(TAG, "handleUsbState startService"); }
            context.startService(intent);
            // tell MediaProvider MTP is connected so it can bind to the service
            context.getContentResolver().insert(Uri.parse(
                    "content://media/none/mtp_connected"), null);
        } else {
            boolean status = context.stopService(new Intent(context, MtpService.class));
            if (DEBUG) { Log.d(TAG, "handleUsbState stopService status=" + status); }
            // tell MediaProvider MTP is disconnected so it can unbind from the service
            context.getContentResolver().delete(Uri.parse(
                    "content://media/none/mtp_connected"), null, null);
        }
    }

MtpService.java

public int onStartCommand(Intent intent, int flags, int startId) {
        mUnlocked = intent.getBooleanExtra(UsbManager.USB_DATA_UNLOCKED, false);//该值为true默认MTP显示文件，否则就算默认MTP也是不显示磁盘内容的
        if (LOGD) { Log.d(TAG, "onStartCommand intent=" + intent + " mUnlocked=" + mUnlocked); }
        synchronized (mBinder) {
            updateDisabledStateLocked();
            mPtpMode = (intent == null ? false
                    : intent.getBooleanExtra(UsbManager.USB_FUNCTION_PTP, false));
            String[] subdirs = null;
            if (mPtpMode) {
                int count = PTP_DIRECTORIES.length;
                subdirs = new String[count];
                for (int i = 0; i < count; i++) {
                    File file =
                            Environment.getExternalStoragePublicDirectory(PTP_DIRECTORIES[i]);
                    // make sure this directory exists
                    file.mkdirs();
                    subdirs[i] = file.getPath();
                }
            }
            final StorageVolume primary = StorageManager.getPrimaryVolume(mVolumes);
            if (mDatabase != null) {
                mDatabase.setServer(null);
            }
            mDatabase = new MtpDatabase(this, MediaProvider.EXTERNAL_VOLUME,
                    primary.getPath(), subdirs);
            manageServiceLocked();
        }

        return START_REDELIVER_INTENT;
    }

private void manageServiceLocked() {
        final boolean isCurrentUser = UserHandle.myUserId() == ActivityManager.getCurrentUser();
        if (mServer == null && isCurrentUser) {
            Log.d(TAG, "starting MTP server in " + (mPtpMode ? "PTP mode" : "MTP mode"));
            Log.d(TAG,"mMtpDisabled " + mMtpDisabled);
            mServer = new MtpServer(mDatabase, mPtpMode);
            mDatabase.setServer(mServer);
            if (!mMtpDisabled) {
               addStorageDevicesLocked();
            }
            mServer.start();
        } else if (mServer != null && !isCurrentUser) {
            Log.d(TAG, "no longer current user; shutting down MTP server");
            // Internally, kernel will close our FD, and server thread will
            // handle cleanup.
            mServer = null;
            mDatabase.setServer(null);
        }
    }

    private void addStorageDevicesLocked() {
        if (mPtpMode) {
            // In PTP mode we support only primary storage
            final StorageVolume primary = StorageManager.getPrimaryVolume(mVolumes);
            final String path = primary.getPath();
            if (path != null) {
                String state = mStorageManager.getVolumeState(path);
                if (Environment.MEDIA_MOUNTED.equals(state)) {
                    addStorageLocked(mVolumeMap.get(path));
                }
            }
        } else {
            for (StorageVolume volume : mVolumeMap.values()) {
                addStorageLocked(volume);
            }
        }
    }