C# – Validating or Validated event

cwinforms

I have some textboxes databound to a BindingSource to custom business object. Databinding is done as the following code-

  txtBookNo.DataBindings.Add("Text", bs, "BookNo", true, DataSourceUpdateMode.OnPropertyChanged, null, "G", GlobalVariables.CurrentCultureInfo);

Now I would like to validate user input. Which event is best for this purpose- Textbox.Validating or Textbox.Validated? And, what should be DatasourceUpdateMode- OnPropertyChanged or OnValidation?

Thanks.

Best Answer

Validating is fired just before the validation process starts, this is the place to put the actual validation code.
Validated is fired after the validation process has finished and is designed to be the place to something based on the validation result.

If DataSourceUpdateMode.OnPropertyChanged is used then:

Data source is updated whenever the value of the control property changes.

If DatasourceUpdateMode.OnValidation is used then:

Data source is updated when the control property is validated, After validation, the value in the control property will also be re-formatted.

If you want only valid (that means it has been validated by your code) data to be sent to your custom business objects you shuld use DataSourceUpdateMode.OnValidation.

Here is an article explaining how to do validation in Windows Forms.

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I found a solution on the MSDN forums. The sample code below will remove all Click events from button1.

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

        button1.Click += button1_Click;
        button1.Click += button1_Click2;
        button2.Click += button2_Click;
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    private void button1_Click(object sender, EventArgs e)  => MessageBox.Show("Hello");
    private void button1_Click2(object sender, EventArgs e) => MessageBox.Show("World");
    private void button2_Click(object sender, EventArgs e)  => RemoveClickEvent(button1);

    private void RemoveClickEvent(Button b)
    {
        FieldInfo f1 = typeof(Control).GetField("EventClick", 
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        object obj = f1.GetValue(b);
        PropertyInfo pi = b.GetType().GetProperty("Events",  
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        EventHandlerList list = (EventHandlerList)pi.GetValue(b, null);
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C# – Winforms DataBinding vs PropertyChanged Event Ordering Issue

The method you're using returns an instance of a Binding. Why not listen to the BindingComplete event of the returned binding and call the Refresh method from there? The code will probably need to evaluate fields such as BindingCompleteContext and Exception to ensure the event is being triggered on a datasource change. You don't need to call listBox.DataBindings.Clear(). The bindings get removed when the control is disposed. You usually don't need to manually unregister the event, and I think in you're case, you don't need to manually unregister the event.

Best Answer

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C# – How to remove all event handlers from an event

C# – Winforms DataBinding vs PropertyChanged Event Ordering Issue

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