为什么在通过canvas.getWidth（）方法进行x坐标处理后，仍未绘制该对象？

Question

I created a class named MyButton, to help me draw rect and doing some actions when its beeing pressed, but when Im passing to the x and y coordinates values, using math on the canvas.getWidth() and canvas.getHeight() method, the button is not being drawn:

This is the methoed to set the coordinates and the height and width of the button:

public void setVars(float x, float y, float width, float height)
    {
        this.x = x;
        this.y = y;
        this.width = width;
        this.height = height;
    }

this is what I tried and didnt work:

this.buttonHint.setVars((float)0, (float)(canvas.getHeight() - canvas.getHeight()/20), (float)(canvas.getWidth()/2), (float)(canvas.getHeight()/20));
this.buttonSuperHint.setVars((float)(canvas.getWidth()/2), (float)(canvas.getHeight() - canvas.getHeight()/20), (float)(canvas.getWidth()/2), (float)(canvas.getHeight()/20));

but when I try this, it works:

    this.buttonHint.setVars((float)0, (float)(20), (float)(canvas.getWidth()/2), (float)(canvas.getHeight()/20));
    this.buttonSuperHint.setVars((float)(20), (float)(20), (float)(canvas.getWidth()/2), (float)(canvas.getHeight()/20));

Answer 1

probably the width/height of the canvas you are calling is still 0 at that time. add some listeners of the width/height of the canvas and make sure it has it's height/width set other than 0, then try calling that button attributes.