QT keyboard event (II) -- long press the key to trigger the event event repeatedly, and the problem is solved

introduction

Qt Keyboard events may encounter unresponsive arrow keys 、 There are problems such as pressing or releasing events all the time , How to solve it ？Jungle The notes will answer for you .

01

Problem description

stay Jungle In my last article （Qt Keyboard events （ One ）—— Detect key input ）,Jungle Simple realization of utilization qt Detect the user's key operation and press the key \ The release operation is printed on Qt A small program on the interface . But there will be a phenomenon during the test , That is to press and hold a key , The interface has been refreshing press、release、press、release……（ Here's the picture ）

in other words , Long press a key without releasing ,keyPressEvent and keyReleaseEvent Events will continue to be triggered . Even though it is Qt Design and implement a good event mechanism , But in terms of user experience , This is unreasonable . What we want to achieve is ： Press a key （ such as Tab key ）, The interface only prints once "Key_Tab Press"; When the hand is released , Only print on the interface "Key_Tab Release".

02

Problem specification

So ,Jungle The query Qt Official documents and several blogs . Official documents mention a QKeyEvent Member function of isAutoRepeat:

You can see , When event From auto-repeating key,isAutoRepeat return true; When event The event comes from the initial key , be sAutoRepeat return false. That may not be easy to understand , Then you might as well Jungle Do a little test ：

stay keyPressEvent Internal printing isAutoRepeat Return value

operation ： Long press Tab key , stay keyPressEvent Internal printing isAutoRepeat Return value , Release Tab Post key , Press and hold again Tab key , Let go again .

void QKeyBoard::keyPressEvent(QKeyEvent *event){
  switch(event->key()){
    case Qt::Key_Tab:
      if(event->isAutoRepeat()==true){
        this->ui.textEdit_press->append("true");
      }
      else{
        this->ui.textEdit_press->append("false");
      }
      this->ui.textEdit_press->append("Key_Tab Press");
      break;
    /*default:
      this->ui.textEdit->append("KeyEvent");*/
  }
}

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The test results are as follows ：

As you can see from the test results , Long press Tab The key is triggered for the first time keyPressEvent When an event is isAutoRepeat return false, Then long press isAutoRepeat The return values are true. Press and hold again after releasing the key ,isAutoRepeat return false, Then long press isAutoRepeat The return values are true. That is, only the first press Tab Key time ,isAutoRepeat The return value is false. Combined with this result Qt Description of official documents , It seems to be better understood .

stay keyReleaseEvent Internal printing isAutoRepeat Return value

Again ,Jungle stay keyReleaseEvent Internal printing isAutoRepeat Return value , The operation results are shown in the figure above （ The code is slightly ）. You can see , Long press Tab key , Automatic triggering keyReleaseEvent When an event is isAutoRepeat return true, Trigger after releasing the key keyReleaseEvent When an event is isAutoRepeat return true.

Test summary

combination Qt Official documents and the above tests , It can be concluded as follows ：

• Key triggered keyPressEvent event ,isAutoRepeat return false; Automatically triggered keyPressEvent event ,isAutoRepeat return true;
• Loose key triggered keyReleaseEvent event ,isAutoRepeat return true; Automatically triggered keyReleaseEvent event ,isAutoRepeat return false.

03

Problem solving

When the real key press and key release events are triggered , Plus right isAutoRepeat Judgment of return value , Specific judgments are as follows 2 Section summary , The sample code is as follows ：

void QKeyBoard::keyPressEvent(QKeyEvent *event){
  switch(event->key()){
    case Qt::Key_Tab:
      if(!event->isAutoRepeat()){
        this->ui.textEdit_press->append("Key_Tab Press");
                /* add your code here*/
      }
      break;
  
    /*default:
      this->ui.textEdit->append("KeyEvent");*/
  }
}
 
void QKeyBoard::keyReleaseEvent(QKeyEvent *event){
  switch(event->key()){
    case Qt::Key_Tab:
      if(!event->isAutoRepeat()){
        this->ui.textEdit_release->append("Key_Tab Release");
                /* add your code here*/
      }
      break;
    /*default:
      this->ui.textEdit->append("KeyEvent");*/
  }
}

Copy

In some blogs , The author may have added a variable to mark whether the key is pressed , And update the mark when pressing and releasing the key . but Jungle I don't think it's necessary , Just add judgment as above . Please visit Jungle Of GitHub Home page ：https://github.com/FengJungle/Qt_Project