How to get the “real” value of the Visible property?

问题

If you set the Visible property of a Windows Forms control to true, that property still returns false if any of the control's parent windows are hidden. Is there a way to get the true, underlying visibility flag of the control in case the parent window is hidden?

回答1:

Well, the regular implementation does check up the control stack, to ensure that all parents are visible. The only way I know to dodge this is to cheat with reflection, and ask for GetState(2), but that is brittle:

    // dodgy; not recommended
    Panel query;
    Form form = new Form
    {
        Controls = {
            new Panel {
                Visible = false,
                Controls = {
                    (query = new Panel {Visible = true})
                }
            }
        }
    };
    form.Show();

    // this is the dodgy bit...
    bool visible = (bool)typeof(Control)
        .GetMethod("GetState", BindingFlags.Instance | BindingFlags.NonPublic)
        .Invoke(query, new object[] { 2 });

回答2:

What I did is temporarily remove the button from its parent controls to check its Visible value and then re-add to the parent controls.

If you need you can track the child index to re-add it at the right index.

回答3:

An option that doesn't rely on reflection would be to recurse through the parents of the control hierarchy looking for one with Visible set to false.

EDIT: See comments for significance of code.

var frm2 = new Form {Text = "Form2"};
var lbl = new Label {Visible = true};
frm2.Controls.Add(lbl);
frm2.Show();

var frm1 = new Form {Text = "Form1"};
var lblVis = new Label { Text = lbl.Visible.ToString(), Left = 10, Top = 10};
lbl.VisibleChanged += (sender, args) => MessageBox.Show("Label Visible changed");
var btnShow = new Button {Text = "Show", Left = 10, Top = lblVis.Bottom + 10};
btnShow.Click += (sender, args) =>
                    {
                        frm2.Visible = true;
                        lblVis.Text = lbl.Visible.ToString();
                        };
var btnHide = new Button {Text = "Hide", Left = 10, Top = btnShow.Bottom + 10};
btnHide.Click += (sender, args) =>
                    {
                        frm2.Visible = false;
                        lblVis.Text = lbl.Visible.ToString();
                    };

frm1.Controls.AddRange(new Control[] {lblVis, btnShow, btnHide});

Application.Run(frm1);

回答4:

I have same issue with classes derived from 'ToolStripItem' base class. so I used Available property value to check if item will be displayed or not. problem solved. Sample:

ToolStripItem curItm = menuStrip1.Items[i] as ToolStripItem;
if(curItm is ToolStripItem && curItm.Available) DoAnyThing();

In this sample 'curItm' is an instance of of ToolStripItem derived class.

This problem with Visible/Enabled properties in .Net controls that depend on parent container's Visible/Enabled must be solved by .Net team. I create a costume property named IsVisible/IsEnabled in my own classes that return assigned value for Visible/Enabled properties and not the value that depend on parent container.

来源：https://stackoverflow.com/questions/391888/how-to-get-the-real-value-of-the-visible-property

标签

.net

winforms

visible