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C# Geting null value from other form [duplicate]

I have two forms. First one has one textbox.Second one has a devexpress data grid.
I want to achieve that:
first click a button and form2 opens.
if I click a row in the data grid in form2, this value should be shown inside the textbox in form1.(form1 is already opened.)
ı m a beginner. thanks for your help.
Form1 frm1 = new Form1();
frm1.textBox1.Text = gridView1.GetFocusedRowCellValue("ID").ToString();
frm1.Show();
when I do that, a new form opens. I dont want to open a new form. Form1 is already opened. I want to add values to its textbox.

Pass form1 as a reference to form2:
In your button click handler on form 1 to open form 2
private void Button_Click(object sender, EventArgs e)
{
Form2 frm2 = new Form2(this);
frm2.Show();
}
form2 code
private Form1 frm1;
// constructor (pass frm1 as reference)
public Form2(Form1 frm1) {
this.frm1 = frm1;
}
//put this in your event handler for a row click in the grid
frm1.textBox1.Text = gridView1.GetFocusedRowCellValue("ID").ToString();

you can try something like this.
When you click on frm1.SimpleButton this function will be called a show your Form2. On Form2 you have to set InnerProperty (from your datagrid?) a when you close Form2 you can use this property.
private void SimpleButton_Click(object sender, EventArgs e)
{
using (Form2 frm = new Form2())
{
frm.InnerProperty = "default text";
DialogResult result = frm.ShowDialog();
SimpleButton.Text = frm.InnerProperty;
}
}

Finally, I solved the problem.
Application.OpenForms["form1"].Controls["textBox1"].Text =
gridView1.GetFocusedRowCellValue("ID").ToString();
Thanks for help.

Switching between forms and sending variable correctly

I am wondering how can I correctly switch between forms by button click event.
I have Form1 and Form2.
Form1 have: -TextBoxForm1
-ButtonForm1
Form2 have: -TextBoxForm2
-ButtonForm2
I would like to on_click ButtonForm1 event go to the Form2. Then I want to write some message to TextBoxForm2 and press ButtonForm2 it will go to the Form1 again and message from TextBoxForm2 will appear in TextBoxForm1.
Everything works fine, but I have one problem. When I close application and I wanna debug and start it again, some errors appear like:"application is already running".
Form1:
public static string MSG;
public Form1()
{
InitializeComponent();
TextBoxForm1.Text = MSG;
}
private void ButtonForm1_Click(object sender, EventArgs e)
{
Form2 form2 = new Form2();
this.Hide();
//There is probably my fault but when I was trying this.Close(); everything shutted down
form2.Show();
}
Form2:
private void ButtonForm2_Click(object sender, EventArgs e)
{
Form1.MSG = TextBoxForm2.Text;
Form1 form= new Form1();
form.Show();
this.Close();
}
How can I do this correctly please? :) I am beginner, thank you!

I would not go the route of using a STATIC for passing between forms as you mention you are a beginner, but lets get the closing to work for you.
In your main form create a new method to handle an event call as Hans mentioned in the comment. Then, once you create your second form, attach to its closing event to force form 1 to just become visible again.
// Inside your Form1's class..
void ReShowThisForm( object sender, CancelEventArgs e)
{
// since this will be done AFTER the 2nd form's click event, we can pull it
// into your form1's still active textbox control without recreating the form
TextBoxForm1.Text = MSG;
this.Show();
}
and where you are creating form2
private void ButtonForm1_Click(object sender, EventArgs e)
{
Form2 form2 = new Form2();
form2.Closing += ReShowThisForm;
this.Hide();
form2.Show();
}
and in your second form click, you should only need to set the static field and close the form
private void ButtonForm2_Click(object sender, EventArgs e)
{
Form1.MSG = TextBoxForm2.Text;
this.Close();
}

Easy solution is to use modal form. Display Form2 temporarily, when it is displayed Form1 is invisible.
var form2 = new Form2();
this.Visible = false; // or Hide();
form2.ShowDialog(this);
this.Visible = true;
And to pass data you can define property in Form2, to example:
public string SomeData {get; set;}
Form1 has to set SomeData, which you take in Shown and display. Same property can be used to get data from Form2 (before closing).
// form 1 click
var form2 = new Form2() { SomeData = TextBoxForm1.Text; }
this.Visible = false;
form2.ShowDialog(this);
this.Visible = true;
TextBoxForm1.Text = form2.SomeData;
// form 2 shown
TextBoxForm2.Text = SomeData;
// form 2 click
SomeData = TextBoxForm2.Text;
Close();

show a form at its current state instead of new form()

I have created a C# application.
Here I have two forms, form1 and form2.
form2 is called from form1.
Later form2 is made hidden.
Now I want to show form2 from form1.
Please give me some idea.

You need to keep reference to Form2 object, and when you want it to be visible, just call frm2.Show() - don't construct the new Form2 object with new Form2() - use the existing one.
// You need to contruct Form2 before calling Show().
Form2 frm2 = new Form2();
// Some handler somewhere
void btnShowForm2_Click(..., ...)
{
frm2.Show();
}
Edit: As Micah pointed out, you will want to hide Form2 instead of closing it:
private void Form2_FormClosing(object sender, FormClosingEventArgs e)
{
this.Hide();
e.Cancel = true; // this cancels the close event.
}

You will want to use form.hide() when hiding form2 instead of form.close
keep a reference to form2 and call form.show when you want to show it again

take form2 instance variable at class level
example
Public Class Form1
{
Form frm2;
//Show form here
protected void Button1_Clik
{
frm2=new Form2();
frm2.Show();
}
//Even the form is hidden, you may show the same instance /same state of form again
protected void Button2_Click()
{
frm2.Show();
}
}

Open an existing form from the main form

I designed two forms: Form1 and Form2. Form1 is the main form. There is a button in Form1, if I click the button, then Form2 will pop out. I want to do something on Form2.
// click button in Form1.
private void button1_Click(object sender, EventArgs e)
{
Form form2= new Form();
form2.ShowDialog();
}
But Form2 is a new form rather than an existing form.
It is wrong.
How? Thanks.

You are creating instance of Form class not the Form2 which you have in your project. Create instance of Form2 which you created earlier and then call ShowDialog in it.
You might have notice the in the program.cs something like Application.Run(new Form1()); Here we create the instance of Form1 and pass to Run method.
Do it this way by creating instance of Form2 and calling ShowDialog() method to show it
Form2 form2= new Form2();
form2.ShowDialog();

You create blank form with
Form Form2= new Form();
You should use
Form2 form2= new Form2();
Complete code:
private void button1_Click(object sender, EventArgs e)
{
Form2 form2= new Form2();
form2.ShowDialog();
}

Declare
Form2 form2= new Form2();
like your class member and use it like this:
private void button1_Click(object sender, EventArgs e)
{
form2.ShowDialog(); //blocking call
//or form2.Show() //non blocking call
}
EDIT
Based on correct comments, to make this work instead of executing the Close() on the function which will lead to Dispose() you need to use form2.Hide() to make is simply invisible

private void button1_Click(object sender, EventArgs e)
{
InputForm form1 = new InputForm();
form1.Show();
}
Here InputForm means which form you want to open.

The question is "Open an existing form from the main form"
Okay lets change it a little, Open an existing instance of form from the main form.
when you show a form
new Form2().Show();
lets say you hid it using
Form2.Hide();
you guys can use this
var Form2_instance = Application.OpenForms.OfType<Form2>().Single();
Form2_instance.Show();

C# windows forms child window creation with VS

Let's say I have a basic form, there's a button and when I click it, it opens a new window.
How can I do this? I tried creating a new form instance on button click event, but it gives me exception, that something is wrong.

Form frm = new Form();
frm.ShowDialog();
//frm.Show();
Or please share your code..

//assuming that ur first form is named Form1 and ur second form is Form2
//assuming that ur button is button1
//inside form1 something like this is shown
Button1.Click += new EventHandler(this.Button1_Click);
void Button1_Click(Object sender, EventArgs e){
Form2 form = new Form2();
//you do either
Form2.Show();
//or focus remains on form2 do this
Form2.ShowDialog();
}
//hope this help