记录于2021-07-30
前不久接到旧项目的维护,其中涉及到了外设连接(平板连接到佳博厂商的称重机),需要实时返回数据到平板上显示。问题就在于数据返回的时快时慢,只能一个一个点去排查了。
打开AS,连接平板,看看日志,这个异常刷都刷不完:
...
java.lang.NullPointerException: Attempt to invoke virtual method 'int com.gprinter.io.PortManager.readData(byte[])' on a null object reference
at com.hycashier.devicelibrary.helper.BluetoothHelper$4.run(BluetoothHelper.java:198)
java.lang.NullPointerException: Attempt to invoke virtual method 'int com.gprinter.io.PortManager.readData(byte[])' on a null object reference
at com.hycashier.devicelibrary.helper.BluetoothHelper$4.run(BluetoothHelper.java:198)
java.lang.NullPointerException: Attempt to invoke virtual method 'int com.gprinter.io.PortManager.readData(byte[])' on a null object reference
at com.hycashier.devicelibrary.helper.BluetoothHelper$4.run(BluetoothHelper.java:198)
...
这一块的代码是这样的:
/**
* 接收数据的方法
*/
public void startReceiveData(){
receiveFlag = true;
/*创建子线程接收串口数据
*/
receiveThread = new Thread(){
@Override
public void run() {
while (receiveFlag){
try {
serialData = "0".getBytes();
byte[] readData = new byte[1024];
int size = portManager.readData(readData);
byte[] realReadData = new byte[size];
System.arraycopy(readData,0,realReadData,0,size);
if (size>0&&receiveFlag) {
serialData = realReadData;
}
getMainHandler().sendEmptyMessage(receiveFlagWhat);
Thread.sleep(intervalTime);
} catch (Exception e){
e.printStackTrace();
}
}
}
};
//启动接收线程
receiveThread.start();
}
通过Debug发现,portManager为空了;而且只有不断的打开新的Activity,就会再次去这里拿实时数据,然后CPU飙升…
也就是说,每一次都会来这个方法中new 一个子线程,并且无休止的取数据(而且这平板性能简直是5-6年前的配置);那么只能试试非空判断了
/**
* 接收数据的方法
*/
public void startReceiveData(){
receiveFlag = true;
/*创建子线程接收串口数据
*/
receiveThread = new Thread(){
@Override
public void run() {
while (receiveFlag && portManager!=null){
try {
serialData = "0".getBytes();
byte[] readData = new byte[1024];
int size = portManager.readData(readData);
byte[] realReadData = new byte[size];
System.arraycopy(readData,0,realReadData,0,size);
if (size>0&&receiveFlag) {
serialData = realReadData;
}
getMainHandler().sendEmptyMessage(receiveFlagWhat);
Thread.sleep(intervalTime);
} catch (Exception e){
e.printStackTrace();
}
}
}
};
//启动接收线程
receiveThread.start();
}
亲测成功,至少cpu降下来了