GWT：检查事件处理程序是否存在
我正在使用按键处理程序根据文本框的字符串值添加和删除事件处理程序。我不想在每个按键上添加或删除事件处理程序。我如何首先检查处理程序是否已存在？
HandlerRegistration firstHandler = null;
HandlerRegistration secondHandler = null;
public void onKeyUp(KeyUpEvent event) {
if (countSpaceChar(textBox.getText()) == 0) {
// code to check if MyFirstHandler is already attached?
firstHandler = textBox.addKeyUpHandler(new MyFirstHandler(this));
} if (countSpaceChar(textBox.getText()) == 1) {
firstHandler.removeHandler();
// code to check if MySecondHandler is already attached?
secondHandler = textBox.addKeyUpHandler(new MySecondHandler(this));
}
}
I'm using a key up handler to add and remove event handlers depending on the string value of a text box. I wouldn't want to add or remove an event handler on every key up. How do I first check if a handler already exists?
HandlerRegistration firstHandler = null;
HandlerRegistration secondHandler = null;
public void onKeyUp(KeyUpEvent event) {
if (countSpaceChar(textBox.getText()) == 0) {
// code to check if MyFirstHandler is already attached?
firstHandler = textBox.addKeyUpHandler(new MyFirstHandler(this));
} if (countSpaceChar(textBox.getText()) == 1) {
firstHandler.removeHandler();
// code to check if MySecondHandler is already attached?
secondHandler = textBox.addKeyUpHandler(new MySecondHandler(this));
}
}
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if (firstHandler != null)将完成这项工作，当您删除处理程序时，将其注册设为 null：if (firstHandler != null)will do the job, and when you remove handler, null it registration: