CODEWITHSUNDEEP
wpfwpf-controls
serhio
serhio

Reputation: 28586

WPF: Determine if a Panel is visible to the user

I have a WPF usercontrol (myGraphicControl) in a tab (WPF application).

When the form size changes, I redraw the graph in myGraphicControl.

Since the redrawing operation is a I need to do it only the control in in the visible tab.

How the WPF (user)control can detect if it's "visible" actually or not?

PS.

by Visible I mean that user can see it. say, if a Visible TextBox is located in the currently invisible tab, this textBox is not visible by the user.

Upvotes: 4

Views: 4248

Answers (3)

ivanatpr
ivanatpr

Reputation: 1880

I've found that while Steve's method generally works, it works much more reliably if you get a point from somewhere in the middle of the child control. I'm guessing that maybe layout rounding somewhere along the way makes the InputHitTest check somewhat inexact. So, change his first line to the following and you're golden:

var childTopLeft = childControl.TranslatePoint(new Point(childControl.RenderSize.Width/2, childControl.RenderSize.Height/2), parentControl);

Upvotes: 2

Marat Khasanov
Marat Khasanov

Reputation: 3848

Maybe UIElement.IsVisible will be helpful? It works for tab contents well. Anyway you can use a solution described here.

I have one more solution. The current implementation of TabControl removes inactive tabs from visual tree. So, another way to determine whether your element is visible is to find PresentationSource. It will be null for elements of inactive tabs.

Upvotes: 1

Steve Greatrex
Steve Greatrex

Reputation: 16009

I don't believe there is a quick-fix solution here, but you may be able to do something using UIElement.InputHitTest(Point).

You could make a call similar to

//get the coordinates of the top left corner of the child control within
//the parent
var childTopLeft = childControl.TranslatePoint(new Point(), parentControl);
//check whether or not the child control is returned when you request the element
//at that coordinate through hit testing
var isVisible = (parentControl.InputHitTest(childTopLeft) == childControl);

However, I should point out that I haven't tried this myself, and that it probably won't work in the following scenarios:

  • Transparent items - generally, transparent backgrounds cause hit testing of a control to pass to the parent
  • Partially occluded items - you can only hit-test one point at a time, so if only part of your child control is visible you will have to check the correct point

Upvotes: 3

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