Return Window handle by it's name / title

Question

I can't solve this problem. I get an error:

The name 'hWnd' does not exist in the current context

It sounds very easy and probably is... sorry for asking so obvious questions.

Here's my code:

public static IntPtr WinGetHandle(string wName)
{
    foreach (Process pList in Process.GetProcesses())
    {
        if (pList.MainWindowTitle.Contains(wName))
        {
            IntPtr hWnd = pList.MainWindowHandle;
        }
    }
    return hWnd;
}

I tried with many different ways and each fails. Thanks in advance.

Solution 1

Update: See Richard's Answer for a more elegant approach.

Don't forget you're declaring you hWnd inside the loop - which means it's only visible inside the loop. What happens if the window title doesn't exist? If you want to do it with a for you should declare it outside your loop, set it inside the loop then return it...

IntPtr hWnd = IntPtr.Zero;
foreach (Process pList in Process.GetProcesses())
{
    if (pList.MainWindowTitle.Contains(wName))
    {
        hWnd = pList.MainWindowHandle;
    }
}
return hWnd; //Should contain the handle but may be zero if the title doesn't match

Or in a more LINQ-y way....

IntPtr? handle = Process
    .GetProcesses()
    .SingleOrDefault(x => x.MainWindowTitle.Contains(wName))
    ?.Handle;
return handle.HasValue ? handle.Value : IntPtr.Zero

Solution 2

As an option to solve this problem:

[DllImport("user32.dll")]
private static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

public IntPtr GetHandleWindow(string title)
{
    return FindWindow(null, title);
} 

Solution 3

Coming several years late to this but, as others have mentioned, the scope of hWnd is only in the foreach loop.

However it's worth noting that, assuming you're doing nothing else with the function, there are two issues with the answers others have provided:

1. The variable hWnd is actually unnecessary since it's only being used for one thing (as the variable for the return)
2. The foreach loop is inefficient as, even after you've found a match, you continue to search the rest of the processes. In actual fact, it'll return the last process it finds that matches.

Assuming that you don't want to match the last process (point #2), then this is a cleaner and more efficient function:

public static IntPtr WinGetHandle(string wName)
{
    foreach (Process pList in Process.GetProcesses())
        if (pList.MainWindowTitle.Contains(wName))
            return pList.MainWindowHandle;

    return IntPtr.Zero;
}

Solution 4

Because you are declaring hWnd inside the if block, it is inaccessible to the return statement which is outside it. See http://www.blackwasp.co.uk/CSharpVariableScopes.aspx for clarification.

The code you've provided can be fixed by moving the declaration of the hWnd variable:

public static IntPtr GetWindowHandleByTitle(string wName)
{
    IntPtr hWnd = IntPtr.Zero;
    foreach (Process pList in Process.GetProcesses())
    {
        if (pList.MainWindowTitle.Contains(wName))
        {
            hWnd = pList.MainWindowHandle;
        }
    }
    return hWnd;
}

Solution 5

hWnd is declared in the foreach loop. Its context is inside foeach loop. To get its value declare it outside foreach loop.

Use it like this,

public static IntPtr WinGetHandle(string wName){
    IntPtr hWnd = NULL;

    foreach (Process pList in Process.GetProcesses())
        if (pList.MainWindowTitle.Contains(wName))
            hWnd = pList.MainWindowHandle;

    return hWnd;
}

View more solutions

Comments

[VixinG]

I tried declaring it before foreach and I got Use of unassigned local variable 'hWnd' in return hWnd line, that's why I asked here.

[Basic]

Then you should initialise it to IntPtr.Zero (see my edit). This is because the window title isn't being matched - so you're never setting the variable which points to an area of memory with undefined contents.

[VixinG]

I see, it should be IntPtr hwnd = IntPtr.Zero; :)

[pinkfloydx33]

That's just a warning in the event that you never assign the variable. You can suppress it in the compiler options, ignore it, or assign it a default value IntPtr.Zero

[VixinG]

It can't be null, because of Cannot convert null to 'System.IntPtr' because it is a non-nullable value type

[Basic]

@VixinG Thanks, nice catch - clearly it's too late and I've had too much coffee to type code without an IDE :) Fixed

[pinkfloydx33]

msdn.microsoft.com/en-us/library/… IntPtr.Zero != null

[AndresRohrAtlasInformatik]

You should add a break inside the if or you will waste a lot of processor time.

[Ivan P.]

So, we are potentially about to iterate over all the active processes. Not sure if it's good

[tigrou]

A much better solution that what is suggested by others answers with GetProcesses() and MainWindowTitle (which sometimes fails).