从另一个表单引用一个表单上的控件

Question

As you can guess, I'm kind of new to .NET and just want to reference a control on one form from another.

Usually I would just do Form.Control.Property but that doesn't work and every example I've found through Google doesn't work for me.

It just seems overly complicated with public classes, etc.

Is there a more simpler way to do this? I'm ready to throw in the towel and just use a global variable at this point.

I have the form containing the control I want to reference, frmGenerate which has a textbox called txtCustomerNo.

From this form through a button's click event I want to show another form, frmCustomers, and have that form reference the value in txtCustomerNo.

frmCustomers.ShowDialog()

It has to be something simple that I'm just not grasping.

Answer 1

In the form with the control you want to reference:

Public Property CustomerNo() As TextBox
    Get
        Return txtCustomerNo
    End Get
    Set(ByVal Value As TextBox)
        txtCustomerNo = Value
    End Set
End Property

In the form you wish to reference the control:

Dim CustomerNo as string = _sourceForm.CustomerNo.Text

It's a bad design to do this, but it's the simplest method - and should set you on your way.

If you are only interesting in the value entered in the text box then the following might be better:

Public ReadOnly Property CustomerNo() As String
    Get
        Return txtCustomerNo.Text
    End Get
End Property

The above will require the second form to have a reference to the actual instance of the first form. Add the below to the second form:

Private _sourceForm as frmGenerate

Public Property SourceForm() As frmGenerate 
    Get
        Return _sourceForm
    End Get
    Set(ByVal Value As frmGenerate)
        _sourceForm = Value
    End Set
End Property

Now you can do the following where you handle the creation and startup of your second form:

Dim customersForm as new frmCustomers
customersForm.SourceForm = Me
customersForm.Show()    

EDIT: I have constructed a sample project for you here:

http://www.yourfilelink.com/get.php?fid=595015

Answer 2

My.Forms.frmGenerate.txtCustomerNo.Text

Answer 3

您需要确保添加的属性是public ，否则其他类将无法访问它们。

Answer 4

You should be able to make whatever you need to reference outside the form public. In many cases that's all that's needed.

Sometimes, it's useful to create a separate public property or method. And have the method take care of the details. For example, if you just want to able able to access the text, you could create a property something like this (in C#).

public string CustomerNo
{
    get
    {
        return txtCustomerNo.Text;
    }
    set
    {
        txtCustomerNo.Text = value;
    }
}

Answer 5

Make a private field. Right click 'Refactor', select 'Encapsulate Field'. This will automatically create a public property for the field.

Another approach is to overload the public constructor.

public CustomersForm(string property1, string property2...)
{
     //Get the properties and do what is necessary.
}

//Parent Form

CustomersForm frmCustomers = new CustomersForm(property1, property2..);

Also sending the complete control to another form is not a good strategy. Share only the fields that are necessary via public properties/constructors.

Answer 6

A better way to approach this is to pass a reference of a control into your class, change any property of it there with your logic, then "send" it back to the calling form.

The trick here is to make sure the class code is using the "ByRef" argument in the called class or else this will not work. In memory you are referencing the same control without creating new properties for it, and that lessens code creep.

For instance here is how you can disable a button from your class code.

In the form, call your class and pass it the button (or any other control):

' new the class your calling
Dim CallClass As New ProgramCall
' pass the control as a by reference argument
CallClass .SetUpTheCall("HOURLY", btnSendToBank)  

Then, in your class:

Public Sub SetUpTheCall(ByVal ParmToPass As String, ByRef btnSendToBank As Button)

' your class logic goes here...

' disable the send button on the calling form
btnSendToBank.Enabled = False

' change the button text on the calling form
btnSendToBank.text = "Disabled"

Answer 7

I save the name of the person logging in to a textbox on the next form after they login like this. My login button has the last lines: Me.Hide() ( Not Me.Close() ) Admin.Show() End

When the user enters a correct username and password, it hides the login form and opens the next page, Admin.vb

In the Admin_Load of the Admin.vb page as the last lines I put:

Dim logged As String logged = Login.txtUser.Text Login.Close(). 'Close hidden login.vb' End Sub

So, the user presses the login button and it hides the login form with the value I want in the txtUser textbox. Then it opens the Admin page. The load event of the Admin page, gets my value from the hidden login page in the txtUser textbox and puts it in the parameter "logged." Once the value is grabbed, it closes the login page and leaves the sub. It all happens in the blink of an eye! Now anywhere I want to use the name of the person that logged in, like in a textbox I just use "logged."

txtchangesby.Text = logged

Very simple and works.

Answer 8

While you can create a property on your second form that will return the data needed, you can just as easily change the Modifier property of that control. By default, the modifiers of controls are private, and therefore not accessible to anything other than the current form. Click on the control, and find the Modifier property. Set that to Public, and you'll be able to access it from outside the form, such as:

Dim f As New SecondForm
f.FirstNameTextBox.Text = "Bob"