Question

I hope that the title and this simple example says everything.

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

    public void UpdateLabel(string str)
    {
        label1.Text = str;
       MessageBox.Show("Hello");
    }

    private void buttonIn_Click(object sender, EventArgs e)
    {
        UpdateLabel("inside");
    }

    private void buttonOut_Click(object sender, EventArgs e)
    {
        MyClass Outside = new MyClass();
        Outside.MyMethod();
    }
}

public class MyClass
{
    public void MyMethod()
    {
         Form1 MyForm1 = new Form1();
         MyForm1.UpdateLabel("outside");
    }
}

When I’m trying to change lable1 from MyClass it does nothing. But I can get to the UpdateLable method from outside, it says Hello to me, it just doesn’t change the label.

Answer 1

Use a delegate for setting your label

public class MyClass {
    Action<String> labelSetter;

    public MyClass(Action<String> labelSetter) {
        this.labelSetter = labelSetter;
    }

    public void MyMethod() {
        labelSetter("outside");
    }
}

.

public void buttonOut_Click(object sender, EventArgs e) {
    var outside = new MyClass(UpdateLabel);
    outside.MyMethod();
}