如何在 C# 事件中区分是代码更改还是用户更改？

Question

I have a simple TextBox that is empty in the beginning. I have a simple event, _TextChanged, to know when the user changed anything in that TextBox . However, the event fires if I do anything with it myself from within code. Like setting textbox.Text = "Test"; or similar.

    private void textNazwa_TextChanged(object sender, EventArgs e) {
        changesToClient = true;
    }

How do I make the event only fire on user interaction and not code changes?

Answer 1

I've been using this process, and it seems to work well. If the event fires and the focus is not in the textbox, then I ignore the request, so when I set the text the focus is elsewhere, but when the user is typing in the textbox, it has the focus, so I acknowledge the changes.

private void textNazwa_TextCanged(object sender, EventArgs e)
{
    if ( !textNazwa.Focused) 
        return; 
}

Answer 2

The event itself does not make a distinction between text entered via user input and text changed via code. You'll have to set a flag yourself that tells your code to ignore the event. For example,

private bool ignoreTextChanged;

private void textNazwa_TextCanged(object sender, EventArgs e)
{
    if (ignoreTextChanged) return;
}

Then use this to set the text instead of just calling Text = "..."; :

private void SetTextboxText(string text)
{
    ignoreTextChanged = true;

    textNazwa.Text = text;

    ignoreTextChanged = false;
}

Judging by your comment to another answer, it sounds like you have quite a number of textboxes. In that case, you could modify the function in this way:

private void SetTextBoxText(TextBox box, string text)
{
    ignoreTextChanged = true;

    box.Text = text;

    ignoreTextChanged = false;
}

Then call it like this:

SetTextBoxText(textNazwa, "foo");

This would accomplish the same thing as just doing textNazwa.Text = "foo" , but will set the flag letting your event handler know to ignore the event.

Answer 3

Well you can't not really anyway. What you can do is remove the handler before you make your change and add it back after you've made the change.

eg

  textNazwa.TextChanged -= textNazwa_TextChanged;
  textbox.Text = "Test";
  textNazwa.TextChanged += textNazwa_TextChanged;

If your method has the same scope as where you're changing the value of the text box as the textNazwa_TextChanged (eg both are in a form) you could set a flag instead or if that's not oopsy enough for you, you could use Chain Of Responsiblity to determine if the textNazwa_TextChanged method should be called

Answer 4

I suggest you use Bindings for your TextBox with a presenter that has properties, so if you need to change your values in the code (for testing for example) you don't to fire events or change to UI code. The only thing you need to do is to set a value on your Presenter.

public class Presenter : INotifyPropertyChanged
{
    public string MyTextValue { get; set; }
    public event PropertyChangedEventHandler PropertyChanged;
    /// Create a method here that raises the event that you call from your setters..
}

And then in you Windows Forms code you need a bindingSource set to your Presenter, and add a Binding to you textBoxes:

EDIT

private BindingSource myPresenterSource ;
this.myPresenterSource = new System.Windows.Forms.BindingSource(this.components);
// Some time later in the

((System.ComponentModel.ISupportInitialize)(this.myPresenterSource )).BeginInit();
// you set the DataSource of your BindingSource
// m_SettingsBindingSource
//
this.myPresenterSource .DataSource = typeof(Presenter );

// and when you create your TextBox you do this :
this.YourTextBox.DataBindings.Add(new System.Windows.Forms.Binding("Text",
   this.myPresenterSource, "MyTextValue", true,
   System.Windows.Forms.DataSourceUpdateMode.OnPropertyChanged));

Then in your InitializeComponent you set the source like this :

myPresenterSource.DataSource = new Presenter();

Check more resources by looking for how to implement the Movel-View-Presenter (MVP) in Windows Forms.

Answer 5

To me I would implement it this way

bool wasUserTyping = false;
private void textNazwa_KeyUp(object sender, KeyEventArgs e){
     wasUserTyping = true;
}

private void textNazwa_TextChanged(object sender, TextChangedEventArgs e){
    if(wasUserTyping){
          //Yaaay!! User did type
    }
}