Best practice for sharing variables across forms in VB.NET

I need to share variables across two forms in VB.NET. One of them is the main form and the other is a child form.

I have been searching, and I have found a few methods. I want to use the best method to do this. I have listed a few options below. Please comment on which one would be the best option:

1. Create a static/shared variable in one of the forms and access it in the other forms via:

   Form1 frm = new Form1(); // Creating object of parent to access shared variable
   frm.a = "abc"; // Passing value
   

2. Send an instance of the main form to the child form when creating the child form. The variables can then be accessed via a property function.

3. Create global variables in a module. This seems like the easiest option, but 开发者_Python百科I doubt it is the best option.

4. I also read something about delegates and events, but I don't know how to implement this.

If there is another method I haven't mentioned, please share it with me.

There is no one answer to the question. All the methods you listed should 'work.' Which you should use depends why you want to share the variable. For example:

1. Say you have a form with a list of records, and the user double-clicks a record, so you want to open a new form to edit the record, and you want to pass the record ID. In this case I would add a constructor method to the second form: Sub New(RecordID as String) 'Add code to load the record here End Sub

2. Say some of the forms in your application may want to know the database path or something else global like that. For that, I would make the appropriate variable on the parent form into a Public variable (called a Field) and access it as MainForm.FieldName. (Disclaimer: Purists will say you shouldn't rely on the somewhat messy fact that VB.NET automatically instantiates an instance of the form class and lets you refer to it by the form name, and that you should instead get a pointer to the actual instance of the form and store it in your child form and access the parent form like that. Actually, this is like number '2' in your post. But it's not actually necessary if you don't mind programmatical incorrectness.)

3. Say there is something global in your app, like the time the app was started, so you can tell the user "You've been using the app for 5 hours, go get a life!" These things could be stored in a module. (Or in the application class but that's quite hidden)

Create two forms. Add 3 radio buttons and 1 button to form1. Add a label to form2. In the code for form1 type

    Public rdb As Integer = 1

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
     Form2.Show()
If RadioButton1.Checked Then
            rdb = 1
        ElseIf RadioButton2.Checked Then
            rdb = 2
        ElseIf RadioButton3.Checked Then
            rdb = 3
        End If
End Sub

Then in form2's code

Private Sub Form2_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Label1.Text = Form1.rdb
    End Sub

Store your global variables in a Module1.vb file, they must be publicly declared to be accessible from all forms:

Public X as String
Public Y as Integer

Then just use them as you would any other variable on any page:

X = "Hello"
Y = 10

Textbox1.Text = X
Textbox2.Text = Y

It's not the safest practice so it shouldn't be used for all your variables. But it is very neat and simple.

The child form can have public get and set functions for a private variable, and the parent form can set it when it changes and its end, or get it before it uses it to see if it has changed in the child form.

You can add public properties to either form. They can access those properties from each other. (That is not called shared though, and is not static in most cases.)

Not sure if this answers the question but one thing I found useful was to refer to the variables in form1 while programming in form2 as Form1.variablename and when in Form1 and referring to variables in Form2 to use in Form1 as Form2.variablename Basically, refer to variables in other forms by putting the name of the form they are in followed by a . and then the variable name