How to invalidate the child panel alone in windows forms?

Question

I have created the two custom panels (ParentPanel and ChildPanel) and added the ChildPanel as children of the ParentPanel. Now i want to invalidate the child panel alone. But while calling ChildPanel.Invalidate(), OnPaint method have been called for both panels (ParentPanel and ChildPanel).

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        private ParentPanel parentPanel;
        public Form1()
        {
        InitializeComponent();

        parentPanel = new ParentPanel();
        parentPanel.Size = new Size(300, 200);
        parentPanel.Location = new Point(3,30);

        var button1 = new Button();
        button1.Text = "Invalidate Child";
        button1.Size = new Size(130, 25);
        button1.Location = new Point(3,3);
        button1.Click += button1_Click;

        this.Controls.Add(parentPanel);
        this.Controls.Add(button1);
    }

    private void button1_Click(object sender, EventArgs e)
    {
        this.parentPanel.ChildPanel.Invalidate();
    }
}

public class ParentPanel : Panel
{
    public ChildPanel ChildPanel { get; set; }

    public ParentPanel()
    {
        BackColor = Color.Yellow;
        ChildPanel = new ChildPanel();
        this.Controls.Add(ChildPanel);

        SetStyle(ControlStyles.OptimizedDoubleBuffer | ControlStyles.Selectable |
                 ControlStyles.UserPaint |
                 ControlStyles.AllPaintingInWmPaint, true);
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        MessageBox.Show("Parent Panel invalidated");
        base.OnPaint(e);
    }
}

public class ChildPanel : Panel
{
    public ChildPanel()
    {
        BackColor = Color.Transparent;
        Anchor = AnchorStyles.Left | AnchorStyles.Top;
        Dock = DockStyle.Fill;

        SetStyle(ControlStyles.OptimizedDoubleBuffer | ControlStyles.Selectable |
                 ControlStyles.UserPaint |
                 ControlStyles.AllPaintingInWmPaint, true);

    }

    protected override void OnPaint(PaintEventArgs e)
    {
        MessageBox.Show("Child Panel Invalidated");
    }
}
}

I have tried to skip the drawing of ParentPanel by using WM_SETREDRAW. But it will suspend drawing of both panels.

[DllImport("user32.dll")]
public static extern int SendMessage(IntPtr hWnd, Int32 wMsg, bool wParam, Int32 lParam);

private const int WM_SETREDRAW = 11;

public static void SuspendDrawing(Control parent)
{
    SendMessage(parent.Handle, WM_SETREDRAW, false, 0);
}

public static void ResumeDrawing(Control parent)
{
    SendMessage(parent.Handle, WM_SETREDRAW, true, 0);
//parent.Refresh();
}

Can anyone please suggest me any solution to redraw the child panel alone without affecting parent?

Thanks in advance.

Regards, Pannir

score -1 · Answer 1 · answered Feb 24 '16 at 12:17

-1

I cant replicate the problem, the child doesnt trigger onpaint for the parent. That message box isnt triggering a repaint is it, or the button press if its on the panel?

answered Feb 24 '16 at 12:17

tim

114
1

Consider providing a comment to OP rather than an other problem in the form of an answer – jolySoft Feb 24 '16 at 12:22
@tim, Just copy paste the first code snippet into the application and run. When click the "Invalidate Child" button, I have invalidated the ChildPanel alone. But OnPaint method is invoked for both panels and shows the message box. – Selvamz Feb 24 '16 at 12:24
A panel onpaint is triggered when another form, such as a messagebox invalidates it. That is not a problem to answer, that is a fact. Invalidating a child control does not trigger an onpaint for the parent another fact. If a button is on the parent panel then pressing it will invalidate the panel it is on, another fact. Please rather than abusing or patronising me, re-read what I said. – tim Feb 29 '16 at 06:11

How to invalidate the child panel alone in windows forms?

1 Answers1