如何删除事件处理程序? [英] How to remove an event handler?

问题描述

我的程序的此阶段有一个绘制到画布上的地图，并提示用户选择他们想要放置项目的位置.

This stage of my program has a map that is drawn to a canvas and the user is prompted to choose the location they would like an item to be placed.

我设置了一个事件处理程序来记录鼠标单击的x，y坐标，但这是我只需要记录一次的事情.

I set up an event handler to record the x,y co-ordinates of the mouse click, but this is something I only need to record once.

这是我当前的事件处理程序:

This is my event handler currently:

EventHandler boatHandler = new EventHandler<javafx.scene.input.MouseEvent>(){
        public void handle(javafx.scene.input.MouseEvent event){
            newX = event.getSceneX();
            newY = event.getSceneY();
            System.out.printf("setOnMouseClicked X = %f, Y = %f\n", newX, newY);
            newX = Math.round(newX/16) *16;
            newY = Math.round(newY/16) *16;
            System.out.printf("Rounded to multiple of 16 X = %f, Y = %f\n", newX, newY);
            if(newX > 0 || newY > 0){
                gc.drawImage(wItemset[0], newX, newY);
            }
        }
    };

检索到x，y值后，我希望事件处理程序停止侦听，但不确定如何.通过阅读其他人的问题，我发现我可以使用以下方式删除事件处理程序:

I would like the event handler to stop listening once I have retrieved the x,y values but I'm unsure as to how. From reading other's questions I've found that I could potentially remove the event handler using:

canvas.removeEventHandler(MouseEvent.MOUSE_PRESSED, boatHandler);

但这不能写在 if 语句中，因此我不确定如何触发它.

But this can't be written within the if statement, so I'm unsure as to how i would trigger it.

记录完x，y值后，我打算为另一个项目准备一个类似的代码块，并且需要确保:

After the x,y values have been recorded, I plan to have a similar block of code for another item and I need to ensure that:

1. 放置正确的物品
2. x，y值用于该项目，而不是前一项

修改:这是我用来添加EventHandler的行

This is the line I used to add my EventHandler

canvas.addEventHandler(MouseEvent.MOUSE_PRESSED, boatHandler);

推荐答案

您可以在事件处理程序中触发它

you could trigger it within your event handler

会是这样的

EventHandler boatHandler = new EventHandler<javafx.scene.input.MouseEvent>(){
        public void handle(javafx.scene.input.MouseEvent event){
        //code used for retrieving x,y values
        canvas.removeEventHandler(MouseEvent.MOUSE_PRESSED, this);

        }
}

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