2个Android蓝牙无法连接的原因和解决方法

错误为： RFCOMM_CreateConnection - already opened state:2, RFC state:4, MCB state:5

原因：socket没有关闭。即使使用了代码socket.close().但是硬件需要时间反应。

解决方法：在socket.close();添加 SystemClock.sleep(POST_RESET_DELAY);等待关闭socket。POST_RESET_DELAY的值可设置为1000，也就是1秒。一秒应当足够了。

另外有时候蓝牙还是无法连接，说socket为空，代码如下：

if(mSocket==null) {

BluetoothCon.this.start();

return;

}

//Sleep time of 1000ms after closing the socket

SystemClock.sleep(POST_RESET_DELAY);

mSocket.connect(); //有一次执行connect的时候 ，显示没有源码。mSocket为null。虽然前面判断了mSocket==null

原因是是使用SystemClock.sleep(POST_RESET_DELAY);之前socket不为空，但是之后由于线程问题，socket为空。

所以使用socket之前要先判断下socket是否为空，如果为空就重新连接。

下面是修改后的代码：

//Sleep time of 1000ms after closing the socket

SystemClock.sleep(POST_RESET_DELAY);

if(mSocket!=null) {

mSocket.connect();

}

else

{

BluetoothCon.this.start();//BluetoothCon中有代码重新为socket赋值

return;

}

另api level 14有函数isConnected()可以判断是否已经连接。

参考资料：
http://stackoverflow.com/questions/7888294/rfcomm-createconnection-already-opened-state2-rfc-state4-mcb-state5?lq=1
Solution

Starting from API Level 14 there is a Method in BluetoothSocket called isConected(),
which returns true, if this socket is already connected and false otherwise, here the original excerpt from the API:

Get the connection status of this socket, ie, whether there is an active connection with remote device.

For API levels < 14 you can work around this issue by putting your Bluetooth Handling Thread to sleep after closing the connection - 1000 ms should be enough, here is an example (btDevice is of the type BluetoothDevice and has been initialized prior to the
code snippet below):

try {
//Open the socket to an SPP device (UUID taken from Android API for createRfcommSocketToServiceRecord)
BluetoothSocket btSocket = btDevice.createRfcommSocketToServiceRecord("00001101-0000-1000-8000-00805F9B34FB");
//Connect to the socket
btSocket.connect();
//Close the socket
btSocket.close();
//Sleep time of 1000ms after closing the socket
SystemClock.sleep(POST_RESET_DELAY);

} catch (Throwable e) {
// Log error message
}