安卓实用开发小知识 1704

水深无声 2022-06-17 01:08 214阅读 0赞

# 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][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][Link 1]，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][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<String, UsbDevice> 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); 
        } 
    }

参考：[https://juejin.im/post/58eaff05ac502e006c43e114][https_juejin.im_post_58eaff05ac502e006c43e114]

[http_blog.csdn.net_nonosama0125_article_details_43160349]: http://blog.csdn.net/nonosama0125/article/details/43160349
[Link 1]: http://georgeyang.cn
[http_blog.csdn.net_yingpaixiaochuan_article_details_53190420]: http://blog.csdn.net/yingpaixiaochuan/article/details/53190420
[https_juejin.im_post_58eaff05ac502e006c43e114]: https://juejin.im/post/58eaff05ac502e006c43e114