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C# forward mouse events to another window without losing focus

My app screencaptures another window that runs on a second monitor. Now I'd also like to forward mouse clicks made in my app to that window. I tried using SendMessage in user32.dll for this, but this also makes window focus switch, which causes some issues, like the two windows rapidly fighting for focus. Is there are way to place those mouse events without making the hidden window active and losing focus on the main app?

Is there are way to place those mouse events without making the hidden window active and losing focus on the main app?
No, there is not even a way to forward mouse input to another receiver. Messages are only part of the input processing. The system also does internal bookkeeping and you cannot replicate that.
The only reliable way to inject input is by calling SendInput. Doing so doesn't allow you to specify a receiver. Input goes to whichever thread is determined to be the receiver by the system.
Although, more often than not, this question is asked when the problem that needs to be solved is a different one altogether: How do you automate a UI? The answer to that question is UI Automation.

Catch when minimize button was pressed on any window

So I'm trying to make window manager that could minimize windows into something like Facebook Messenger chatheads. For that i need to catch minimize event on any window that is open when my program starts, or will be opened later. And that's the tricky part, at least for me. The only way I could think of was global hooks, but as far as I know, they are only applied to windows that are currently opened and not the ones that will open later, which means i would have to actively look for any new windows and hook into their wndproc too which would be performace heavy. Also as I was reading about hooks, I found that it's discouraged to use them as they rather heavily impact performance.
So my question is what is the best way to catch minimize events?
Thanks in advance,
Ignas

WinForms MdiChildren Selection and Activation

I am a fairly experienced WinForms developer. I have an MdiApplication that used to work well. However, recently the main shell of the application, for which we use ComponentOne RibbonForm, has been updated in a big way. This update did affect some of our other 3rd party components, which we established was due to ComponentOne's use of DoEvents() in their event code. I thought I had cleaned up all of the code causing problems but I now have found another...
When I have multiple MdiChildren open and select one of these in code from an button click event on the ribbon form via
document.Activate();
document.EditorControl.Select();
document.EditorControl.Focus();
the other open MdiChildren documents still have focus, that it the forms are highlighted and input is not set on the document I set in code. Two questions:
How can I ensure that the Form I want to make active is the only one that is active?
Linking to the above; setting one form as active using form.Activate() should deactivate the others MdiChildren, but it is not - how can I deactivate the other windows in code?
Thanks for your time.

[Too long for a comment]
I am sick to the hind teeth with fighting C1. Esp. the Ribbon. I have confirmed with their support that they do use DoEvents() which they use to yield on their Gui threads. I am now going to switch to DevExpress which should be straight forward for my MVC application...
C1's use of DoEvents() messes up the normal flow of your application. DoEvents() is asynchronous which means it terminates before the application has actually processed any outstanding events, so if you're using it in a procedure with many sequential statements, calling DoEvents() causes a huge disturbance whenever it's called. This is what I think we are seeing when we perform our MDI operations, but we can never be sure without the C1 source code.
I hope this helps.

c# detect which messagebox (originated in another app) button has been pressed

Another application displays a messagebox (with a unique text inside it), user chooses Yes/No.
How to detect what he pressed in c#? (best in .Net up to 3.5). I could do polling with FindWindowEx (on another thread) but how to detect what button had been pressed? Also I don't think polling is the best way to do the job.
I need to know what the user has chosen in another app, so I can react accordingly in my own app. I don't have access to the other app's source code. Also to make it clear I don't want to click any of the buttons myself. I'm not afraid of a bit of c++, winapi and pinvoke

To monitor UI events in another application you can use UI Automation. To solve your specific problem you need to subscribe to a particular event (see Subscribing to UI Automation Events). To do so call IUIAutomation::AddAutomationEventHandler with a UIA_Invoke_InvokedEventId Event Identifier.
While UI Automation can be used to solve your problem, it is an assistive technology, mainly to enable accessibility needs and automated UI testing.

You could use either Anonymous or Named Pipes or WCF(Windows Communications Foundation).

Handling WM_ events in a windowless C# process

I've been looking around for quite a while, and can't seem to find a good way to do this.
Basically I have a C# process using WPF (which has no visible window), that I need to handle WM_ events in (such as WM_CLOSE or WM_DESTROY for example; so that I can elegantly shutdown when a user chooses to log off or restart their machine).
There are a number of solutions I've seen out there that suggest using System.Windows.InteropServices to call AddHook and provide it a pointer to a function that then becomes the WndProc. The problem with this is, as far as I can tell, it depends on the window actually being visible (and in this case there is no window).
Another way that's suggested but doesn't work is to override the WndProc method of a WinForm, but this process has no visible forms or windows.
I've also found things referring to a Message-only Window. Some kind of invisible window that still receives WM_ events. From what I've seen, this is only available in a Microsoft.WindowsCE.Forms assembly. I added a reference to this assembly in my project and subclassed MessageWindow as indicated at: http://msdn.microsoft.com/en-us/library/microsoft.windowsce.forms.messagewindow.aspx but it still seems to not work. The breakpoints inside the WndProc are not being hit.
Any clue?

Think about what you are asking- if you don't have a window, how could your application receive a window message (considering that messages are sent to a window's handle).
That's like saying "how can I receive email without having an email address?"
Michael Entin covers windows' behavior during shutdown here.
I am 99% sure that all processes running in a user's session are automatically closed when the user logs off anyway, so this shouldn't be an issue. If you really must handle this window message, you can create a hidden window as per Any way to create a hidden main window in C#?