文本框输入更改时如何获取行大小以刷新

Question

I have a line that gets drawn on canvas based on the user inputs for the length of the line. The line appears just fine but when I change the number in the textbox, a new line is just drawn on top of the first line without getting rid of the first one.

I've tried calling the method in different places with no luck. Im a beginner so this is all new. I did not use MVVM for this project.

Here is where the user enters the number:

<TextBox PreviewTextInput="NumberValidationTextBox" Text="{Binding ycoord}" Name="y" TextChanged="Y_TextChanged" Height="20" Width="40" Grid.Row="2" Grid.Column="2"/>

Here's my C#:

private double yval;

    public double ycoord
    {
        get => yval;
        set
        {
            yval = value;               
            heightline();

        }
    }

public void heightline()
    {

           Line heightline = new Line();

            heightline.Stroke = new SolidColorBrush(Colors.SteelBlue);
            heightline.StrokeThickness = 2;

            heightline.X1 = 510;
            heightline.Y1 = 110;
            heightline.X2 = 510;
            heightline.Y2 = 110 + rect.Height;
            main.Children.Add(heightline);       

    }

rect.Height is another method that uses the same textbox to create a rectangle but it resizes based on aspect ratio so I need to use rect.Height to draw the line in order to maintain the same height as the rectangle.

expected results are the line refreshes automatically to the new size as soon as the textbox has been changed. This does happen, but the old one stays on the canvas underneath the new line.

Answer 1

You can try to find the line in the canvas and if does not exist add it, otherwise update it:

public void heightline()
{
    List<UIElement> uIElements = mycanvas.Children.Cast<UIElement>().ToList();

    UIElement heightline = uIElements.Where(p => p.Uid == "myLine").FirstOrDefault();

    if (heightline == null)
    {
        heightline = new Line();
        heightline.Uid = "myLine";
    }


        heightline.Stroke = new SolidColorBrush(Colors.SteelBlue);
        heightline.StrokeThickness = 2;

        heightline.X1 = 510;
        heightline.Y1 = 110;
        heightline.X2 = 510;
        heightline.Y2 = 110 + rect.Height;

    if(uIElements.Count == 0)
    {
        mycanvas.Children.Add(heightline);
    }
}