如何创建一个持续更新的文本框，以在添加项目后立即显示更新的小计？

Question

I want to create a textbox that, when a new value is added to a variable (for example: Price1 is assigned the value of 3.5), a textbox with the code

CheckP7_TextChanged(sender As Object, e As EventArgs) Handles checkP7.TextChanged
        Dim subTotal As Double
        subTotal = (price1 * quant1 * taxRate) + (price2 + quant2 + taxRate)
    End Sub

would calculate the subtotal continuously until the user presses the checkout button. How would I go about doing this?

As far as I've tried, I can only get the textboxes to update when clicking a button saying "Calculate".

I expect the output to just continuously update the textbox with the current subtotal until the user hits either "Calculate" or "Checkout".

(eg I have 2 hotdogs in the cart, each at a price of $2.5 . The subtotal shows $5 [before taxes], and I add a hamburger at $3.5 each. The subtotal is immediately updated to show the new price [$8.5])"

Answer 1

As far as I can tell by interpreting your current implementation, you are trying to achieve a real-time calculation/display on Winform/WPF -- correct me if i am wrong...

In general, you can achieve the real time calculation/display by handling the various events of the controls, but i would advise you to try create your won view/business models that implement INotifyPropertyChanged interface: * if any of the properties (like price, quantity, etc.) is changed, then raise a property changed event * and also raise a property changed event for the property of "Total"

and in your frontend, just bind all the fields to the various controls, with two way bindings.

so all the input at frontend will be taken into the object and causes a chain of updating, which would eventually result in the display of the total/sub-totals..

i believe you could find plenty of examples online...