QTouchEvent always called 4 times with any interaction

Question

QTouchEvent always called 4 times with any interaction with the screen. Even if i just touch the screen for a 0.1 second (not moving and not released the finger). So i can`t get an information when the touch is actually was ends or updated.

bool ChartPlotter::touchEvent(QTouchEvent* ev) {

    switch (ev->type()) {
       case QTouchEvent::TouchBegin: {
           __android_log_write(ANDROID_LOG_WARN,"","begin");
       }
       case QTouchEvent::TouchUpdate: {
        __android_log_write(ANDROID_LOG_WARN,"","update");
    }
       case QTouchEvent::TouchEnd: {
             __android_log_write(ANDROID_LOG_WARN,"","end");
    }
 ...

and the output when i just touched the screen (i not moved the finger, and not released it, i just touched and holded it on on the same place)

W   : begin
W   : update
W   : end
W   : end
``

Answer 1

You are missing a break for each case , because like this it will go trough all cases.

You don't need a {} for the case, it's fine like this:

bool ChartPlotter::touchEvent(QTouchEvent* ev) {

switch (ev->type()) {
   case QTouchEvent::TouchBegin:
       __android_log_write(ANDROID_LOG_WARN,"","begin");
   break;

   case QTouchEvent::TouchUpdate: 
       __android_log_write(ANDROID_LOG_WARN,"","update");
   break;

   case QTouchEvent::TouchEnd:
       __android_log_write(ANDROID_LOG_WARN,"","end");
   break;
}
...

Since you make a TouchBegin event, it prints out all 3 logs (since there is no break to stop them), and once you release the press, TouchEnd is triggered and because of that you have end printed out two times.