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Showing Winforms on dual-screen setup

I have a winforms application in C#, with about 10 forms to navigate through.
On all of them, I have set StartPosition as CenterScreen but I use a laptop with a second screen plugged in.
Now the application starts randomly on one of my screens. Also even if the app is on one screen, MessageBoxes pop up on the second one. How can I set the application to always start at the main screen, the one set as "1" in Windows.
I also want to bind the application to the screen it is showing at so that MessageBoxes would appear on the same screen as the app. Another thing I would like to have is so that new forms would show on the same position as previous forms, not going back to the screen where the application started.
What should I use to control the positions of the forms?
I tried changing StartPosition to CenterParent, but that doesn't seem to change anything.

Try this out on starting page ( first form):
private void MyForm_Load(object sender, EventArgs e)
{
this.Location = Screen.AllScreens[0].WorkingArea.Location;
this.StartPosition = FormStartPosition.CenterScreen;
}
More information here : Showing a Windows form on a secondary monitor?
This question is about showing program on secondary screen. just change 1 index to 0 on arrays if you used answers of that.
Edit:
Just for emphasize Bryce Wagner comment for other people read this question :
If you're calling it from a form or user control, you'll want to call MessageBox.Show(this, "Message") instead.

Combining all answers here and in similar questions, the working solution for showing app on primary screen is this:
private void FormLogin_Load(object sender, EventArgs e)
{
this.Location = Screen.AllScreens[0].WorkingArea.Location;
ReallyCenterToScreen();
}
protected void ReallyCenterToScreen()
{
Screen screen = Screen.FromControl(this);
Rectangle workingArea = screen.WorkingArea;
this.Location = new Point()
{
X = Math.Max(workingArea.X, workingArea.X + (workingArea.Width - this.Width) / 2),
Y = Math.Max(workingArea.Y, workingArea.Y + (workingArea.Height - this.Height) / 2)
};
}
And to keep the MessageBoxes on the center screen is this:
MessageBox.Show(this, "Message")
Sources are the comment of #Bryce Wagner to my question, the answer from #Mohamad Shahrestani and from this question answer by #Sarsur.A

I have a laptop with a second screen. Windows 10 is in "Extend" mode. None of the code examples helped with my dialog ignoring the manual location.
It turns out that NVidia has some helpful options in their driver. One will decide for you where you want your form or your dialog. If your code just doesn't seem to behave, try the "nView Desktop Manager" -> "Windows Manager" -> "Dialog box repositioning" and Open windows on settings.

C# Two windows on desktop, one window fixed on right - fullscreen is smaller

I creating desktop application in C#. I need fixed window same as image on right, and another windows have size in maximized mode in have width = fullwidth - myWindow.
How do you make it?
Im tried next code, it work good, but another fixed is fullscreen, and my app on top. I need windows fullscreen state as fullwidth - mywindow.
StartPosition = FormStartPosition.Manual;
foreach (var scrn in Screen.AllScreens) {
if (scrn.Bounds.Contains(Location)) {
Height = scrn.WorkingArea.Height;
Location = new Point(scrn.Bounds.Right - Width, scrn.Bounds.Top);
return;
}
}

C# Switch off or cover duplicated monitor

I'm developing an app in C#. This app will run on a PC and also in a WACOM tablet, which is a duplicated monitor of the PC.
I want to switch off or cover the tablet with an image because the client can't see the beginning and the end of the process. When the time is right, the tablet will turn on or the screensaver will be removed so that the client can interact and, once the client's actions are finished, the WACOM tablet returns to the initial state. How can I do this?
I've been searching and I've found how to switch off the principal monitor but I don't know how to switch off only the tablet. Also some kind of screensaver would be right, but I didn't found how to put an image only in one screen.

You didn't mention the framework you are working, assuming you can reference WinForms, here is a way to show a form maximized on a specific screen:
System.Windows.Forms.Screen[] screens;
screens = System.Windows.Forms.Screen.AllScreens;
System.Windows.Forms.Screen selectedScreen = screens[1]; // choose your preffered monitor
// Sets the form to show maximized on the selected screen:
form.Left = currentScreen.Bounds.Width;
form.Top = currentScreen.Bounds.Height;
form.StartPosition = FormStartPosition.Manual;
form.Location = currentScreen.Bounds.Location;
Point p = new Point(currentScreen.Bounds.Location.X, currentScreen.Bounds.Location.Y);
form.Location = p;
form.WindowState = FormWindowState.Maximized;
form.Show();
If you disable form borders and have a PictureBox docked to "Fill" displaying your selected image you will achieve your intended goal and cover your tablet screen with an image.

Form Position (set OnLoad) different when program installed

I have a Windows Forms application that I use the following code to dock it to the lower-right side of the screen when it is launched:
protected override void OnLoad(EventArgs e)
{
var s = Screen.FromPoint(this.Location);
this.Location = new Point(s.WorkingArea.Right - this.Width,
s.WorkingArea.Height - this.Height);
base.OnLoad(e);
}
When I am in Visual Studio debug mode, this works like a charm. When I build an installer and install the application (on the same dev box) and run it, the coordinates are slightly different and the form is not perfectly docked in the corner. So I stuck this in the OnLoad:
MessageBox.Show(this.Location.X + "x" + this.Location.Y);
In development mode it displays 1355x720 but when I install it displays 1365x730
Why the discrepency? Obviously I could just subtract 10 for my code to work but I would like an explanation for this behavior.
Update:
This machine is Windows 8.1 Pro 64-bit with multiple monitors.
It is the form size that is different (not Screen.WorkingArea). In development mode the form size shows 245x140 but when I install it shows 235x130
I am also unable to give the form focus. There is a textbox on the form that receives focus onload. It has the blinking caret, but I cannot type until I physically click on the textbox. This again only happens when I install it; works fine when run from VS. I suspect this is related to the form position going off the screen edge.
The form has TopMost set to True

How to fix the size of a C# Windows Form Application from resizing

I have a C# Windows Form application that I am working on and when I build the form on the development PC it looks fine but when I move the exe onto another machine everything resizes. This then through's out the picturebox and button controls. I have specified the size of the controls in VS but it seems to ignore these. I have also fixed the minimum and maximum sizes to be the same but this has not resolved the issue.
Can anyone point me the direction of something that I have missed as I need to fix the size of the controls.
Thanks in advance.
New PC
Development PC
this.interviewPb.Image = ((System.Drawing.Image(resources.GetObject("interviewPb.Image")));
this.interviewPb.Location = new System.Drawing.Point(771, 366);
this.interviewPb.Margin = new System.Windows.Forms.Padding(3, 2, 3, 2);
this.interviewPb.Name = "interviewPb";
this.interviewPb.Size = new System.Drawing.Size(393, 492);
this.interviewPb.TabIndex = 9;
this.interviewPb.TabStop = false;

Try setting the AutoScaleMode property for the form to none. This should prevent resizing even if the DPI resolution is different on different machines.