C# WinForms - Cannot access a control in a handler method-CodePudding

I have a form containing two flow layout panels (FLP), which dynamically have buttons added to them. These buttons are actually a class called tagButton which inherits from Button and I have added a handler in the constructor for the click() method. On click, I want to remove the button from the FLP it is currently in then add it to the other FLP.

Below is a trimmed down version of my code for the tagButton class. Note that the tagButton class is defined inside the of the form class both FLPs are in:

    class tagButton : Button
    {
        public string tag = "";
        public bool useTag = false; //tells you which FLP the button is in

        public tagButton(String tag, Boolean useTag)
        {
            this.tag = tag;
            this.Text = tag;
            this.useTag = useTag;

            this.Click  = TagButton_Click;
        }


        private void TagButton_Click(object sender, EventArgs e)
        {
            tagButton tagButton = (tagButton)sender;
            tagButton.useTag = !tagButton.useTag;

            if (tagButton.useTag)
            {
                flowLayoutPanel.Controls.Remove(tagButton);
            }
        }
    }

I'm having problems with the last line:

flowLayoutPanel.Controls.Remove(tagButton);

I can switch it to the following and it works, however there is no way for me to add it to the other FLP. Or at least, not without doing Parent.Parent.Parent.Controls[1]... etc which is clearly a bad idea.

tagButton.Parent.Controls.Remove(tagButton);

I've tried switching different classes and methods to static but nothing I tried worked, the this keyword doesn't seem to work either.

CodePudding user response：

I would recommend having a separate class overriding a parent control that's aware of both FlowLayoutPanels. Then, when your button wants to switch, it can find that custom control in its parents and invoke a custom "switch" function that would move the invoking button from the list it's in to the list it wasn't in.

CodePudding user response：

One of many ways to achieve this outcome is to have MainForm expose a static array of the FlowLayoutPanel candidates as Panels property:

public partial class MainForm : Form
{
    public static Control[] Panels { get; private set; }
    char _id = (char)64;
    public MainForm()
    {
        InitializeComponent();
        Panels = new Control[]{ flowLayoutPanelLeft, flowLayoutPanelRight, };
        buttonAddLeft.Click  = (sender, e) =>
        {
            flowLayoutPanelLeft.Controls.Add(new tagButton
            {
                Height= 50, Width=150,
                Name = $"tagButton{  _id}",
                Text = $"Button {_id}",
            });
        };
        buttonAddRight.Click  = (sender, e) =>
        {
            flowLayoutPanelRight.Controls.Add(new tagButton
            {
                Height= 50, Width=150,
                Name = $"tagButton{  _id}",
                Text = $"Button {_id}",
            });
        };
    }
}

Then, suppose you want to swap between panels when a tagButton gets a right-click (for example).

class tagButton : Button 
{
    protected override void onm ouseDown(MouseEventArgs e)
    {
        base.OnMouseDown(e);

        if (MouseButtons.Equals(MouseButtons.Right))
        {
            Control dest;                if(Parent.Name.Contains("Left"))
            {
                dest = MainForm.Panels.First(_=>_.Name.Contains("Right"));
            }
            else
            {
                dest = MainForm.Panels.First(_ => _.Name.Contains("Left"));
            }
            Parent.Controls.Remove(this);
            dest.Controls.Add(this);
        }
    }
}