安卓实用开发小知识 1704

Edittext设置android：focusable=“false”禁止输入之后，再次用setFocusable(true)无法输入，可通过以下方法令edittext重新获得焦点可输入文字:

edittext.setFocusable(true);//—设置edittext是否可以获得焦点
edittext.setFocusableInTouchMode(true);//—设置edittext在touch模式下是否可以获得焦点
edittext.requestFocus();//—调用该方法给指定的view或者它的子view焦点。如果这个view在isFocusable()方法下返回false，或者isFocusableInTouchMode()方法下返回false，这个view不会真正获得焦点
edittext.requestFocusFromTouch();//—调用这个给指定的view或者它的子view焦点。这个特别的变异于（？）requestFocus（）的方法会让在这个view被touch时，给view焦点。

参考：http://blog.csdn.net/nonosama0125/article/details/43160349

RecyclerView嵌套RecyclerView离开界面再回来时，位置变动博客出处，里面的RecyclerView抢先获取到焦点，导致界面上一到item的顶部，解决办法是在外部的RecyclerView加上:

android:descendantFocusability=”blocksDescendants”

关于descendantFocusability
beforeDescendants：viewgroup会优先其子类控件而获取到焦点
```
afterDescendants：viewgroup只有当其子类控件不需要获取焦点时才获取焦点
blocksDescendants：viewgroup会覆盖子类控件而直接获得焦点
```

参考：http://blog.csdn.net/yingpaixiaochuan/article/details/53190420

安卓USB开发
1.发现设备

UsbManager usbManager = (UsbManager) context.getSystemService(Context.USB_SERVICE);
Map usbList = usbManager.getDeviceList();

2.授权

if (!usbManager.hasPermission(usbDevice)) {
       usbPermissionReceiver = new UsbPermissionReceiver();
       //申请权限
       Intent intent = new Intent(ACTION_DEVICE_PERMISSION);
       PendingIntent mPermissionIntent = PendingIntent.getBroadcast(context, 0, intent, 0);
       IntentFilter permissionFilter = new IntentFilter(ACTION_DEVICE_PERMISSION);
       context.registerReceiver(usbPermissionReceiver, permissionFilter);
       usbManager.requestPermission(usbDevice, mPermissionIntent);
        }
 private class UsbPermissionReceiver extends BroadcastReceiver { 
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if (ACTION_DEVICE_PERMISSION.equals(action)) {
                synchronized (this) {
                    UsbDevice device = intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
                    if (device.getDeviceName().equals(usbDevice.getDeviceName()) {
                        if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)) {
                          //授权成功,在这里进行打开设备操作
                        } else {
                          //授权失败
                        }
                    }
                }
            }
        }
    }

3.获取输入输出端口

usbInterface=usbDevice.getInterface(0);
for (int index = 0; index < usbInterface.getEndpointCount(); index++) {
                UsbEndpoint point = usbInterface.getEndpoint(index);
                if (point.getType() == UsbConstants.USB_ENDPOINT_XFER_BULK) {
                    if (point.getDirection() == UsbConstants.USB_DIR_IN) {
                        usbEndpointIn = point;
                    } else if (point.getDirection() == UsbConstants.USB_DIR_OUT) {
                        usbEndpointOut = point;
                    }
                }
            }

4 数据传输

usbDeviceConnection = usbManager.openDevice(usbDevice);
//发送数据
int ret = usbDeviceConnection.bulkTransfer(usbEndpointOut, data, data.length, DEFAULT_TIMEOUT);
//接收数据
int inMax = inEndpoint.getMaxPacketSize(); 
ByteBuffer byteBuffer = ByteBuffer.allocate(inMax); 
UsbRequest usbRequest = new UsbRequest(); 
usbRequest.initialize(connection, inEndpoint); 
usbRequest.queue(byteBuffer, inMax); 
if(connection.requestWait() == usbRequest){ 
    byte[] retData = byteBuffer.array(); 
    for(Byte byte1 : retData){ 
        System.err.println(byte1); 
    } 
}