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Open and close forms through a menu c#

I've had a look around but none of the answers make any sense to me. I have a menu form which has buttons on; when users come to use the menu form, you can open other forms from the menu. Currently, I can get the form to open, but the menu form stays open too.
private void BtnAddNewCar_Click(object sender, EventArgs e)
{
AddCompanyCar carForm = new AddCompanyCar();
carForm.ShowDialog();
}
The code above opens the form AddCompanyCar from the menu. How do I add to this code so that the form 'Menu' closes when AddCompanyCar opens?

Are you sure want to do this as it impacts usability. If you're using WinForms, then just create a container window, and replace the panels instead. Might be easy and best way
If not and you wanna go-ahead, can take a look on this example

Why not just hide it, then show it again when ShowDialog() returns?
private void BtnAddNewCar_Click(object sender, EventArgs e)
{
this.Visible = false;
AddCompanyCar carForm = new AddCompanyCar();
carForm.ShowDialog(); // execution stops here until "carForm" is dismissed
this.Visible = true;
}

by closing the main window, you destroy the context in which you were previously working. As others suggest, simply hide the main window so you can return to it.

Whats the best way to switch form in C#

So in the project I'm planning, the user will be switching between different screens frequently. These different screens will have different controls with different functions, and really nothing in common.
Should I create a form for each screen and just form.close and form.show(?) to switch screen? Or is it better to keep hiding and showing certain controls, so if a user wants to go to form B from form A, all of form A's controls disappear, and form Bs controls appear? I don't need to know how to do it, I just need to know which is the recommended or proper way, since I haven't really seen it anywhere.

You shouldn't use
form.close();
as this will close the current form (and if its your main form, exit the application) use
form.hide();
instead. An example is given below
from Form1:
private void btnModify_Click(object sender, EventArgs e)
{
Form mod = new modifyForm();
mod.Owner = this;
mod.Show();
this.Hide();
}//end btnModify_Click
from modifyForm:
private void btnCancel_Click(object sender, EventArgs e)
{
this.Owner.Show();
this.Close();
}

You can also try using the TabControl. You can group your different screens into the different tab items. All you have to do is drag it to the form and edit its content in the Properties window.

MDI application issues

General description of application:
Main form as MDI Container. On application start, if there is no xml file for database configuration (it is checked in Main form) Main form i call another form as showdialog() to fill all database info to build connection string. Then i close form and open another for login, then i get back to Main form, which has Split Container (2 panels: 1-menu on top, 2-content from child forms).
I open forms with:
private void PlanButton_Click(object sender, EventArgs e)
{
plan.TopLevel = false;
KontenerMenu.Panel2.Controls.Add(plan);
plan.Dock = DockStyle.Fill;
plan.Show();
}
and close form with:
private void Plan_FormClosing(object sender, FormClosingEventArgs e)
{
e.Cancel = false;
this.Hide();
}
Problems i have with app:
1. When i hit Cancel button when i open ShowDialog() form for database app crashes. Cancel button is simply:
private void cancelButton_Click(object sender, EventArgs e)
{
Application.Exit();
}
2. I have problem with clicking button to open/close/open again child forms. When i hit 'X' and want o open, app crashes with exception that it cannot refer to non-existing object
3. I have several buttons when i hit one and then another one it is always below the first one and not on the top
4. For example my form is 200x200 and in right down corner i have button (so location let's say 190x190) and i hit maximize button. My button is still on 190x190 and i would like to have it on down right corner. I couldn't find any property for that. Is there any or i have to write some code for that.

I'm not sure I understood your questions. Please make them clear.
But as an answer to question #4, there's an anchor property that does what you want.

Instead of trying to exit the application from within the dialog form itself you should return a DialogResult value and test that in the main form. The cancel button on the dialog doesn't need any code, just set its DialogResult property to 'Cancel' and if you have an Ok button set its DialogResult to 'OK'.
DialogForm f = new DialogForm();
DialogResult r = f.ShowDialog();
if (r == DialogResult.Cancel)
{
Close();
}

I can immediately see a number of problems with you code, including:
If you're going to add controls dynamically using Controls.Add, you should make sure the controls you're adding are dynamically created using new(). I get a sense that you don't have a clear understanding of object lifetimes and the WindowForms control life cycle.
The Application.Exit method should be used only in unusual cases. It's purpose is to achieve exactly the result you're observing - to immediately "crash" the application. The easiest way to have a button close a modal dialog is the set the DialogResult property of the button.
Winforms has a very elegant system for placement of control on a variable sized window. In order to use this system, you should familiarize yourself with the Anchor and Dock properties that are available on all controls.
It looks like what you're doing is attempting to learn WinForms by trial and error. You can do this, but it will take much longer and be much more painful that getting a hold of a good tutorial, book, or perhaps even attending a class if you can manage it. That will allow you to take these issues one at a time and have a much more enjoyable learning experience.

Click to new window.xaml

im learning wpf for the first time,
i have made this far
private void Button_Click(object sender, System.Windows.RoutedEventArgs e)
{
// TODO: Add event handler implementation here.
}
lets say its my click button 'home' some how i have made a new window store.xaml at the same product.
how can i connect them ?
heres a sc

Your question seems a bit vague to me, if you simply want to display the store inside the same window you should not implement the content of the window directly but only use the window as a shell for your content, if your store is a window as well you should refactor it into a UserControl which then can be added to the window.
You can also use Pages, see the Navigation Overview for more info on that.

How do you return the focus to the last used control after clicking a button in a winform app?

I'm working on a windows forms application (C#) where a user is entering data in a form. At any point while editing the data in the form the user can click one of the buttons on the form to perform certain actions. By default the focus goes to the clicked button so the user has to click back on to the control they want to edit in order to continue modifying the data on the form. What I need to be able to do is return the focus to the last edited control after the button click event has been processed. Here's a sample screenshot that illustrates what I'm talking about:
The user can be entering data in textbox1, textbox2, textbox3, etc and click the button. I need the button to return the focus back to the control that most recently had the focus before the button was clicked.
I'm wondering if anyone has a better way of implementing this functionality than what I've come up with. Here's what I'm doing right now:
public partial class Form1 : Form
{
Control _lastEnteredControl;
private void textBox_Enter(object sender, EventArgs e)
{
_lastEnteredControl = (Control)sender;
}
private void button1_Click(object sender, EventArgs e)
{
MessageBox.Show("Do something here");
_lastEnteredControl.Focus();
}
}
So basically what we have here is a class variable that points to the last entered control. Each textbox on the form is setup so the textBox_Enter method is fired when the control receives the focus. Then, when the button is clicked focus is returned to the control that had the focus before the button was clicked. Anybody have any more elegant solutions for this?

For a bit of 'simplicity' maybe try.
public Form1()
{
InitializeComponent();
foreach (Control ctrl in Controls)
{
if (ctrl is TextBox)
{
ctrl.Enter += delegate(object sender, EventArgs e)
{
_lastEnteredControl = (Control)sender;
};
}
}
}
then you don't have to worry about decorating each textbox manually (or forgetting about one too).

You could do the following
Change the button to a label and make it look like a button. The label will never get focus and you don't have to do all the extra coding.

I think what you're doing is fine. The only thing I could think of to improve it would be to store each control into a stack as they are accessed. That would give you a complete time line of what was accessed.

Your approach looks good. If you want to avoid having to add an the event handler to every control you add, you could create a recursive routine to add a GotFocus listener to every control in your form. This will work for any type of control in your form, however you could adjust it to meet your needs.
private void Form_OnLoad(object obj, EventArgs e)
{
AddGotFocusListener(this);
}
private void AddGotFocusListener(Control ctrl)
{
foreach(Control c in ctrl.Controls)
{
c.GotFocus += new EventHandler(Control_GotFocus);
if(c.Controls.Count > 0)
{
AddGotFocusListener(c);
}
}
}
private void Control_GotFocus(object obj, EventArgs e)
{
// Set focused control here
}

Your implementation looks good enough -- what I do want to know is why you want to do this in the first place? Won't it be preferrable for the focus to cycle back to the first entry? Is the data in the last text box so malleable that once they click the button it is "remembered"? Or do you have some sort of operation that the button does to that specifici text box data -- in that case shouldn't the focus go to a subsequent control instead?
I'm interested in finding out why you want to do this in the first place.

Yeah, I admit the requirement is a bit unusual. Some of the information that the users will be entering into this application exists in scans of old documents that are in a couple of different repositories. The buttons facilitate finding and opening these old docs. It's difficult to predict where the users will be on the form when they decide to pull up a document with more information to enter on the form. The intent is to make the UI flow well in spite of these funky circumstances.

Create a class called CustomTextBox that inherits from TextBox. It has a static variable called stack. When the textbox loses focus push onto the stack. When you want to find the last focused control then just pop the first item from the stack. Make sure to clear the static Stack variable.