How can I tell if a given hWnd is still valid?

c# winforms handle hwnd
Ian P picture Ian P · Apr 29, 2010 · Viewed 14.8k times · Source

I'm using a third-party class that spawns an instance of Internet Explorer. This class has a property, hWnd, that returns the hWnd of the process.

Later on down the line, I may want to reuse the instance of the application if it still exists, so I need to tell my helper class to attach to it. Prior to doing that, I'd like to know if the given hWnd is still valid, otherwise I'll spawn another instance.

How can I do this in C# & .NET 3.5?

Answer

Francisco Soto picture Francisco Soto · Apr 29, 2010

If it is a window handle, you can call isWindow(hWnd);

From msdn:

Return Value

BOOL

If the window handle identifies an existing window, the return value is nonzero.

If the window handle does not identify an existing window, the return value is zero. Remarks

A thread should not use IsWindow for a window that it did not create because the window could be destroyed after this function was called. Further, because window handles are recycled the handle could even point to a different window.

By the way since you are in .NET you'll have to do something like:

[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool IsWindow(IntPtr hWnd);

Related questions

How to capture mousemove events beneath child controls

I am trying to handle a mouseclick event on a particular form that should fire if the mouse cursor falls between a set of coordinates - lets say a square. I understand that if I had an empty form I …

Read More
How do I make a textbox that only accepts numbers?

I have a windows forms app with a textbox control that I want to only accept integer values. In the past I've done this kind of validation by overloading the KeyPress event and just removing characters which didn't fit the …

Read More
ComboBox: Adding Text and Value to an Item (no Binding Source)

In C# WinApp, how can I add both Text and Value to the items of my ComboBox? I did a search and usually the answers are using "Binding to a source".. but in my case I do not have a …

Read More