从另一个 class c# 调用方法

Question

I have a simple problem when calling methods in another classes.
I have a lot of similar code in different class files and I thought that I could create a global class with methods that I use often.
But I don't know how to do it correctly.
Please check my code below and tell me what it could be wrong.
In addtion, please tell me if I could do it differently?.
The Form1 contains only one button.

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

    public void ChangeTextInButton1(string newText)
    {
        button1.Text = newText;
    }
    private void Button1_Click(object sender, EventArgs e)
    {
        GlobalMethods gm = new GlobalMethods();
        gm.ChangeTextButtonFromOtherClass();
    }
}

public class GlobalMethods
{
    public void ChangeTextButtonFromOtherClass()
    {
        Form1 f1 = new Form1();
        f1.ChangeTextInButton1("NEW BUTTON NAME");
    }
}

}

When I call the methods works perfect and the string is passed to the ChangeTextInButton1() but the Text in button does not change and I don't know why.

Answer 1

instead of creating a new form, you should provide a reference to the existing one in order to modify it. To do this inject the dependency to the constructor of GlobalMethods :

class GlobalMethods
{
    private readonly Form1 form;
    public GlobalMethods(Form1 f) { this.form = f; }
}

Now you can reference that form within your ChangeTextButtonFromOtherClass -method:

public void ChangeTextButtonFromOtherClass()
{
    this.form.ChangeTextInButton1("NEW BUTTON NAME");
}

Finally you need to provide that reference from within your click-eventhandler:

private void Button1_Click(object sender, EventArgs e)
{
    GlobalMethods gm = new GlobalMethods(this);
    gm.ChangeTextButtonFromOtherClass();
}

Alternativly to passing the reference to the constructor of GloablMethods you can also provide it to the ChangeTextButtonFromOtherClass -method itself.

Answer 2

You are creating a new instance of From1 within you GlobalMethods.

So if you expect that the existing instance of Form1 from where you call globalmethods is going to change, then this is incorrect.

If you want to "share" code like this then static methods is one way to do this. So you also don't need to create a new GlobalMethods instance each time, and then you just pass in the Form1 instance you want to update.

public static class GlobalMethods
{
    public static void ChangeTextButtonFromOtherClass(Form1 f1)
    {
        f1.ChangeTextInButton1("NEW BUTTON NAME");
    }
}

(I assume that there are no other methods in this class and that you don't need to initiate an instance of it for other purposes)

Having said that. If it is only really 1 line of code, as simple as this, then although you are technically breaking the "Do not repeat yourself" rule, it is not worth having a new class to do this. Just repeat the same single line of code.

Having said that!

If you have multiple forms which do exactly this same thing. Then you should instead create a new Form class which implements this functionality, and then all your forms can inherit from that new Parent Form instead.