Re: Access Controls from another class - C# Discussion Boards

4-Feb-06 9:07

I have one form Form1 with some controls. How can I access from Class1 controls in Form1?
I've found that I should to write in Class1 something like this:

class Class1
{
    Form1 _frm1;
    public Class1()
    {
    }

    public Class1(Form1 frm1) : this()
    {
        _frm1 = frm1;
    }
    
    public Form1 frm1
    {
        get
        {
            return _frm1;
        }
        set
        {
            _frm1 = value;
        }
    }
    public void test()
    {
        frm1 = new Form1();
        frm1.comboBox1.Items.Add("test"); // Don't work
    }
}
class Form1
{
    private void callFunctionFromForm()
    {
         Class1 cls1 = new Class1(this);
         cls1.test();
    }
}

This code return no errors, but does not adds "test" to comboBox1...

-- modified at 15:10 Saturday 4th February, 2006

kasik4-Feb-06 11:00

kasik

4-Feb-06 11:00

Try changing the test() function to this:

public void test()
{
    _frm1.comboBox1.Items.Add("test");
}

Cheers,
Will H

tray_gator4-Feb-06 22:44

4-Feb-06 22:44

Thank for anwer, but...dont work Frown | :(

as I undestand right:
class Class1
{
public Class1()
{
}

public Class1(Form1 frm1):this()
{
_frm1 = frm1;
}
public Form1 frm1
{
get
{
return _frm1;
}
set
{
_frm1 = value;
}
}
public void test()
{
_frm1 = new Form1();
_frm1.comboBox1.Items.Add("test"); //dont work
}
}
class Form1
{
public comboBox comboBox1;
public void aaa()
{
Class1 cls1 = new Class1(this);
cls1.test();
}
}

-- modified at 4:51 Sunday 5th February, 2006

Colin Angus Mackay4-Feb-06 15:22

4-Feb-06 15:22

The Form will expose a property called Controls, you can use that to access the controls on the form. You cannot access the control fields directly as they are private or protected.

ColinMackay.net
"Man who stand on hill with mouth open will wait long time for roast duck to drop in." -- Confucius
"If a man empties his purse into his head, no man can take it away from him, for an investment in knowledge pays the best interest." -- Joseph E. O'Donnell

tray_gator4-Feb-06 22:51

4-Feb-06 22:51

First of all Thanks for answer. Your way looks like good and simple Smile | :)

but how does it works?
I have public comboBox1 in Form1
from Class1 I try to access it so:
Form1 frm1 = new Form1();
Console.WriteLine( frm1.Controls.ContainsKey("comboBox1") ); // return false
also by accessing so:
Console.WriteLine(frm1.Controls["comboBox1"].Height) ..returns error: Object reference not set to an instance of an object. Frown | :(

mav.northwind4-Feb-06 23:52

mav.northwind

4-Feb-06 23:52

Controls.ContainsKey("comboBox1") ?
How did you get this to compile? The Controls property of a Control doesn't have a ContainsKey method and a string indexer.

Indeed, you could iterate over the Controls collection, but in your case this isn't a good idea because it'll completely depend on the contents of the collection at run time.

I think you should add a public property to your Form1 class to access the comboBox1 control.

Regards,
mav

--
Black holes are the places where god divided by 0...

tray_gator5-Feb-06 0:41

5-Feb-06 0:41

It has

I cannot find something now in MSDN, but if u will type frm1.Controls.ContainsKey(... it will write:
bool ControlsCollection.ContainsKey(string key)
(frm1 is instance of Form)
but maybe I am wrong and dont understand something general, because I am really new in objective-oriented programming.

In Form1 I have such a code:

public comboBox _comboBox1; 
public comboBox comboBox1; // the comboBox which is displaing
{
    get
    {
       return _comboBox1;
    }
    set
    {
       _comboBox1 = value;
    }
}
public void aaa()
{
    Class1 cls1 = new Class1();
    cls1.test();
}

in Class1 I call comboBox1 so:

public void test()
{
    Form1 frm1= new Form1();
    frm1.comboBox1.DataSource = new string[] {"aaa", "bbb"};
}

but that dont works Frown | :(

.. if you will have a little time, please write some very-very short example... Smile | :)

kasik5-Feb-06 1:28

kasik

5-Feb-06 1:28

In your first post you had a function in your Form1 class like this:

private void callFunctionFromForm()
{
    Class1 cls1 = new Class1(this); // <-- pass the form to cls1 through its constructor
    cls1.test();
}

Now in Class1, you have a variable called _frm1. In Class1's constructor, you do this:

public Class1(Form1 frm1) : this()
{
    _frm1 = frm1;
}

This sets your local variable _frm1 to point at the form that you want altering. Now in your test() method in Class1, you do this:

Form1 frm1= new Form1();
frm1.comboBox1.DataSource = new string[] {"aaa", "bbb"};

The first line of this creates an entirely new form. You then edit this forms combobox. Then the method exits and you loose this form. You need to edit the form that you passed in the constructor, not a new one. If you remove the first line, and then change the second to

_frm1.comboBox1.DataSource = new string[] {"aaa", "bbb"};

it should work. If it doesn't then I must have completely missunderstood your meaning Poke tongue | ;-P

Cheers,
Will H

-- modified at 7:53 Sunday 5th February, 2006

tray_gator5-Feb-06 2:04

5-Feb-06 2:04

Thank You Very Much!! It helped. Works perfectly! Thanks again... Smile | :)

mav.northwind5-Feb-06 3:07

mav.northwind

5-Feb-06 3:07

Oh I see, you're using .NET 2.0 where Control.ControlCollection has been modified compared to 1.1/1.0.

But nevertheless, although it's easily possible to access another Form's controls directly (for example by making them public or exposing a public property for them), it's better style (and easier to maintain/modify) if you don't rely on a certain control to display your data but let the other Form handle it.

So instead of writing something like

frm1.comboBox1.DataSource = new string[] {"aaa", "bbb"};

(given that comboBox1 is visible, of course) I'd suggest NOT exposing comboBox1 but instead adding a property to transfer the strings to display, for example similar to this:

...somewhere in Form1...
protected string[] _choices;
public string[] Choices
{
  get { return _choices; }
  set
  {
    _choices = value;
    comboBox1.DataSource = value;
  }
}

and then in your test write:

frm1.Choices = new string[] { "aaa", "bbb" };

That way you've separated your data from the presentation of this data and can easily change the comboBox to a different control for showing your strings without breaking compatibility with your callers.

Regards,
mav

--
Black holes are the places where god divided by 0...

tray_gator5-Feb-06 4:22

5-Feb-06 4:22

Thanks for answer, I think its better way too.
I dont know why, but by me that dont works...
I do so:

class Form1
{
    private comboBox comboBox1; //its visible
    protected string _choices;
    public string[] Choices
    {
        get  {  return _choices;  }
        set
        {
            _choices = value;
            comboBox1.DataSource = value;
        }
    }
    public void someFunctionInForm1
    {
         Class1 cls1 = new Class1();
         cls1.test();
    }
}
class Class1
{
    public void test()
    {
        Form1 frm1 = new Form1();
        frm1.Choices = new string {"aaa", "bbb"}; // dont work
    }
}

If I make the same from Form1 class:

...somewhere in Form1
Choices = new string[] {"ccc", "ddd"}; // Works

all works, but when I do this in Class1 (like above) - dont work.

kasik5-Feb-06 4:57

kasik

5-Feb-06 4:57

You're doing it again. In your test() method you still have this:

public void test()
{
    Form1 frm1 = new Form1(); // <--!
    frm1.Choices = new string {"aaa", "bbb"};
}

Remove the first line, as it is creating a new instance of Form1, and refer to the instance that you've stored locally from the constructor call (called _frm1 i think?).

Cheers,
Will H

tray_gator5-Feb-06 6:04

5-Feb-06 6:04

Thanks, I've thinked after creating properties I can access it so Smile | :)

but then I dont understand what is the advantage of using properties to access controls? Because in this case its look like the same, but through property.

Colin Angus Mackay5-Feb-06 10:42

5-Feb-06 10:42

Back in November I blogged about why you should use properties rather than just make the field public[^].

ColinMackay.net
"Man who stand on hill with mouth open will wait long time for roast duck to drop in." -- Confucius
"If a man empties his purse into his head, no man can take it away from him, for an investment in knowledge pays the best interest." -- Joseph E. O'Donnell

tray_gator5-Feb-06 22:05

joining the server with my application

5-Feb-06 22:05

Thanks. Very good article.

moonangel_bio4-Feb-06 7:39

moonangel_bio

4-Feb-06 7:39

hi,
i'm a beginner in c# & SQL server 2000, and i did a project with them but i need to make an .exe file that don't force the user to have sql or any thing else.
just to run the exe and he can use the project.
thanx

Colin Angus Mackay4-Feb-06 15:18

4-Feb-06 15:18

If you want to embed the database in your setup program then SQL Server isn't going to work for you. As the name suggests it is a server product. There is MSDE which can be distributed with your application but I think it is still a separate install.

You might want to consider something more along the lines of Vista DB[^]

ColinMackay.net
"Man who stand on hill with mouth open will wait long time for roast duck to drop in." -- Confucius
"If a man empties his purse into his head, no man can take it away from him, for an investment in knowledge pays the best interest." -- Joseph E. O'Donnell

[Message Deleted]

emran8344-Feb-06 19:48

emran834

4-Feb-06 19:48

[Message Deleted]

Colin Angus Mackay4-Feb-06 23:45

4-Feb-06 23:45

emran834 wrote:
Is that you meant My application will be running stand alone in the user's computer or The user must have SQL server installed !!

The latter, SQL Server must be installed.

emran834 wrote:
Whenever i build my solution, the RELEASE Folder is Stand Alone and My .mdf file is inside the RELEASE Folder which made sense to me that it will run stand alone. Ain't I right ?

No, that isn't right. The database file is useless without SQL Server to open it and server data from it and allow changes to it. In your application you never access the file directly. SQL Server is the only thing that accesses the file. Your application accesses SQL Server not the file.

ColinMackay.net
"Man who stand on hill with mouth open will wait long time for roast duck to drop in." -- Confucius
"If a man empties his purse into his head, no man can take it away from him, for an investment in knowledge pays the best interest." -- Joseph E. O'Donnell

moonangel_bio5-Feb-06 1:42

moonangel_bio

5-Feb-06 1:42

i don't think that user must have SQL in his PC.
i need a way to let the project stand alone without SQL
am i obvious !!!?
thanx

Colin Angus Mackay5-Feb-06 1:51