How Can I Access and Modify Form Controls from Another Form in C#?

Accessing a Form Control from Another Form

Problem

Accessing controls from one form in another can be challenging. Consider two forms, "Form 1" with a ListBox and "Form 2" which needs to access its SelectedIndex property.

Best Practice Solution

Rather than using a Singleton pattern, consider passing a reference from one form to another. This allows direct communication between them.

Example

In Form1:

// ...
public int MyListBoxSelectedIndex
{
    set { lsbMyList.SelectedIndex = value; }
}
// ...

In Form2:

// ...
private Form1 mainForm; // Reference to "Form 1"

public AddNewObjForm()
{
    InitializeComponent();
    mainForm = new ControlForm();           
}

public void SomeMethod()
{
    mainForm.MyListBoxSelectedIndex = -1;
}
// ...

Alternative Solution with Passing a Reference

Another approach involves passing a reference from Form1 to Form2, allowing Form2 to modify the LabelText property of Form1's Label control:

Form1:

// ...
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        Form2 frm = new Form2(this); // Pass reference to Form2
        frm.Show();
    }

    public string LabelText
    {
        get { return Lbl.Text; }
        set { Lbl.Text = value; }
    }
}
// ...

Form2:

// ...
public partial class Form2 : Form
{
    public Form2()
    {
        InitializeComponent();
    }

    private Form1 mainForm = null;
    public Form2(Form callingForm)
    {
        mainForm = callingForm as Form1; // Cast to Form1
        InitializeComponent();
    }

    private void Form2_Load(object sender, EventArgs e)
    {
        this.mainForm.LabelText = txtMessage.Text; // Modify LabelText
    }

    private void button1_Click(object sender, EventArgs e)
    {
        // ...
    }
}
// ...

The above is the detailed content of How Can I Access and Modify Form Controls from Another Form in C#?. For more information, please follow other related articles on the PHP Chinese website!