从 C# 中的另一个表单类更改按钮的文本

Question

I want to modify something in Mission Planner and I want to change button from another class/form in C# in this function :

public void CloseAllConnections()
{
    myButton1.Text = "Disconnecting all";

    ... 
}

function that is located in :

namespace MissionPlanner
{
    public partial class MainV2 : Form
    {
        ...
    }

    ...
}

the idea is that everything works perfectly when i am focused on that menu, but sometimes i get a error

i even made a function like this

public MyButton GetMyButton1 { get { return myButton1; } }

and also created new instance

var myObject = new MainV2(true);
myObject.myButton1.Text = "Disconnecting all";

nothing works ...

i don't even know where is the function called from, because is clear that is not called from MainV2 class ...

An exception of type 'System.NullReferenceException' occurred in MissionPlanner.exe but was not handled in user code

Any ideas? Thank you.

Answer 1

You need to grab an instance of the form where the button resides. Do this by saving a static reference to the form in it's constructor:

namespace MissionPlanner
{
    public partial class MainV2 : Form
    {
        public static MainV2 CurrentForm;
        public MainV2()
        {
            CurrentForm = this;
            InitializeComponent();
        }

Then somewhere else in your code:

public void CloseAllConnections()
{
    MainV2.CurrentForm.myButton1.Text = "Disconnecting all";

    ... 
}

Answer 2

It appears that your click event form object is called (name) myButton1, and that you are calling the following to change it: myobject.myButton1.Text = "Disconnecting all". Try using myButton1.Text = "Disconnecting all" instead.

Answer 3

One thing that you could try is to pass the button from the form to the class that will be modifying the button.

public class Example
{
    public Button MyButton1 { get; set; }

    public Example(Button myButton1)
    {
        MyButton1 = myButton1;
    }

    public void CloseAllConnections()
    {
        MyButton1.Text = "Disconnecting all";
    }
}

This should successfully set the button's text on MainV2.

Answer 4

Are you using any sort of multi-threading in your app? if so: Make sure you either only change the button from the same thread it was created by, or simply use the ControlInstance.Invoke() method to delegate the change.