How to make events for changing custom made properties (custom control)

问题

I have custom control inheriting from TextBox class , and i have added some properties , for example i have property placeHolderText and i want to have some event which will occur when i change that text?
Like these events

And there is my property in designer view

How to achieve that?

回答1:

To create an event in C# you can follow Standard .NET event patterns.

To create a Changed event for a Something property of a custom control, you can follow these steps:

• Declare an event SomethingChanged. It can be any delegate, as a general delegate you can rely on EventHandler delegate or EventHandler<T>, in case which you want to have a specific event argument rather than using EventArgs.
• Create a protected virtual OnSomethingChanged method which accepts the event args and is responsible to raising the event. So you should raise the event in body if this method.
• In the property setter, check if the value is different from current value, assign it and call OnSomethingChanged to raise the event.

Example

public EventHandler PlaceHolderChanged;
string placeholder;
public string PlaceHolder
{
    get { return placeholder; }
    set
    {
        if (placeholder != value)
        {
            placeholder = value;
            OnPlaceHolderChanged(EventArgs.Empty);
        }
    }
}
protected virtual void OnPlaceHolderChanged(EventArgs e)
{
    PlaceHolderChanged?.Invoke(this, e);
}

来源：https://stackoverflow.com/questions/51004364/how-to-make-events-for-changing-custom-made-properties-custom-control