As you can see, the class names I used are default names of classes generated by Visual C#. How can I go about changing values in a TextBox named "textBox2" (this TextBox is placed in the Form1 design already) from the "Program" class? I have tried a lot of things and every thing I tried results in this error (or similar to): An object reference is required for the non-static field, method, or property 'WindowsFormsApplication1.Form1.textBox2'
Please, if you can, try to keep your answers simple, thank-you.
First, you generally shouldn't access controls such as textboxes from your Program class. Instead you should do this in the Form1.cs file. Form1 is a class, and it has a protected field for textBox2 so it is inaccessible outside the class. If you want to change the value from Program.cs, you should add a public function to Form1 that sets the value of textBos2.Text.
Secondly, you appear to be just typing class names instead of the name of the instance. The difference is Textbox is a class, textBox1 and textBox2 are instances. Textbox.Text is invalid because you need to specify WHICH textbox you are trying to get or set the text for. It's the same with Form1.textBox2. Form1 is a class and there can be many of them. You must specify the name of the instance of the form to access its public members.
UPDATE:
I'm just going to give you a brief explanation of the difference between a class and an instance of a class, static fields and non-static fields. Please forgive any wordiness.
When you create a new windows forms application Visual Studio will create a Form1 type for you. Form1 is a class. Program then uses Form1 to create a form instance and show it. The code would look something like:
Form1 form = new Form1;
In this case, form is the instance. You can create multiple instances of Form1. Each instance will have the textBox2 you created, which is an instance of the Textbox class. Just like you have to do textBox2.Text to get the text of the second Textbox you created on the form, you must specify form.textBox2 (or your public method that sets the textBox2.Text value). Form1, even though it has a number after it is a class, and form is the instance. They have the same relationship as Textbox and textBox2.
Non-static members are accessible to an instance. Static members are accessible to the class. A static member can not access a non-static member unless it is through an instance.
You'll need to have an instance of your Form1 to do this.
Form1 frm = new Form1();
Then you'll have to build a public method to access to your textbox, cause it's a private member.
Form1.cs:
public void UpdateText(string newValue)
{
this.textbox2.Text = newValue;
}
Finally:
frm.UpdateText("new text");
You have to create a new instance of the Form1 class.
You can't "reach" a non static var without new()
var form1 = new Form1();
form1.textBox2.Text= "aaa";
Make textBox2 public or internal. To do so adjust the Modifier property of it from the designer (Properties). Then do this in Main from "Program" class:
Form1 f = new Form1();
f.textBox2.Text = "sdfsdf";
Application.Run(f);
This is absolutely a bad design anyways.. Tell us why you would want this, we would be helpful in dealing with the real problem.
Related
I have a public class A in a file called A.designer.cs and there is a textbox object called Textbox1 in there that I want to use. It is declared as:
public DevExpress.XtraGrid.Views.Grid.GridView textbox1
I want to use it in my b.cs file, which is of a public partial class b. How do I call the Textbox1 in class A?
I tried
A.Grid.GridView.textbox1.Text = "hi"
but it is giving me the error that the file
"does not contain a definition for "grid"".
It's a public instance member of class A so you need an instance A and you can then access its textbox1 field. You've already done this same thing a hundred times before with various other members of various other types. Why try to make it harder this time?
the scenario doesn't make much sense to me but if that's the case.. Do it as usual.
//get a instance of A, something like
A a = new A();
//access by:
a.textbox1
But really you may want to think about why accessing a gridview from outside.
I have in my opinion thoroughly looked for the answers in this website, but unfortunately I haven't found any or I just suck at looking at it.
I have 2 forms and 1 controller class and 1 model class or data class. In addition, ControllerClass has an array of the model class.
In Form1 I did a reference to the controller like this:
ControllerClass control = new ControllerClass();
In Form2 I want to reference from the ControllerClass I referred to in Form1.
Until now I have been doing something like:
ControllerClass control = new ControllerClass();
in Form2 but this just makes a new copy of the ControllerClass which is not very helpful to me.
So how can I use the ControllerClass that I instantiated in Form1 in Form2?
If you only need a single object from a class, you could use a singleton.
Then ofc, you will always have the same object.
There are several ways how you can implement your control as a singleton
here some examples:
http://csharpindepth.com/articles/general/singleton.aspx
For C# i prefer the nested version.
If you don't want to pass the object to other forms through the constructor (Communicate between two windows forms in C#), as others have suggested here, you can use a static object within the Form1.
For example, you could declare
public static ControllerClass control = new ControllerClass();
and then access the object like:
ControllerClass temp = Form1.control;
You can also make a second, static, class which will have the ControllerClass object (the class should be in the same namespace and not in the Form1 class), like so:
public static class ControllerStaticClass
{
public static ControllerClass control = new ControllerClass();
}
Then you can access the ControllerClass object like:
ControllerClass temp = ControllerStaticClass.control;
I have a function named private void QuizReset() on a form called FormMain and I was wondering if there was a way to access it on a form named Form2 without getting build errors? Might seem like a really simple question or something I'm missing, but I've tried changing it from private to public and I mustn't be doing it right as I get build errors and such. I'm all up for modifying it if it can be done without errors. If anyone could help me out that'd be great.
Thank you.
The current code for the function is:
private void QuizReset()
{
//resets the difficulty selection control and shows it again upon resetting the quiz
difficultySelectionControl.Reset();
difficultySelectionControl.BringToFront();
btnNext.Enabled = false;
lblStatus.Text = "Please select a difficulty";
iCorrectACount = 0;
iCurrentQIndex = 0;
}
If you want to access the method it can't be private. static public is a simple work around. Then you can call it with MainForm.LoadQuiz(). Another option is to move the logic into a helper class.
Put them in a public common class. Then put LoadQuiz function as a private static method that belongs to that class. You can also make LoadQuiz a static public, which is quick and dirty. I don't recommend that, because exposing methods publically could cause memory and allocation problems down the road.
I think you cannot put this function in common static class, because, if I understand right, the function use a controls of the form(btnNext.Enabled = false;). This mean that function can/must be used only with instance of the FormMain class.
If you want call this function from Form2, then Form2 must to have a reference of FormMain.
My approach will be next:
Create a variable in Form2:
private FormMain frmMain;
Then create a constructor of Form2 where i assign a reference of FormMain in Form2
public Form2(FormMain inFrmMain)
{
this.frmMain = inFrmMain;
}
Code for opening of Form2 will be then:
Form2 frm2 = New Form2(this);
frm2.Show();
After this you can call your FormMain function from Form2:
this.frmMain.QuizReset()
And of course, at first change function QuizReset to public
I search a easy way to access different controls on different forms without any workarounds like I would do this e. g. in Visual Basic 6.
Example:
Form3.pictureBox1.Image = MyImage;
But somehow C# doesn't allow accessing another controls on another forms not even from my own classes. I already changed the "pictureBox1" in Form3 to public and still C# doesn't know this control if I type "Form3.".
What I have to do, to access my controls? I already run Visual Studio with elevated privileges (Microsoft answered me on my question in their support area, that elevated privileges are important for accessing the other forms and the controls on it) but nothing helped me sofar. So I stay now with the one form always in C# and this is not suitable to develop any application. Most applications need multiple forms and therefor should be a easy way to access controls from any context in a class or another form. I don't want to use any "set...or get properties" - I do not know even how! Somewhere I found this specific workaround but I usually have so many controls and labels to access in my application, that this would generate a lot of useless overhead, if each control property needs a get- and set-statement or whatever to write to it.
Maybe someone of you knows a more elegant method to do this in a more simple way even if elevation needed.
In VB6 you could access the default instance of your form by using the Class name, in VB.Net they have continued that behavior. C# doesn't have that behavior, therefore you have to create your own instance of your Form. Otherwise you are trying to use it like a static Class. Even though you do not want to, the best way to do want you want is to expose them through properties it keeps everything encapsulated.
Form3 frm3 = new Form3();
frm3.pictureBox1.Image = Image.FromFile("ImageName");
frm3.Show();
I think I know what is wrong. Form1 and Form3 are in fact classes, so typing Form1.something means that something must be a static member. In order to be able to access the picture, you need an instance of the class.
To explain this better, here is an example:
string a;
string is the class type, and a is an instance of that class.
A method to do this would be to modify the startup code (in windows forms that would be in the Program.cs source file), and save the form in a static class, and access it from there.
This is what Program.cs probably looks like:
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1());
}
You can see that a new instance of Form1 is being created, that is what the new keyword does. You could also do the following:
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Form1 f = new Form1();
Application.Run(f);
}
The variable f contains the form being displayed.
I don't really know how your program works, but anyway... to be able to access members of Form3, you need to find the instance. Maybe you have new Form3().Show() somewhere in your code, I don't know exactly... but you need to save that to a variable, and that's how you can access it.
You need to change the modifier property of the objects to public, than you make a instance of the form and call the object you want
Form2 frm2 = new Form2();
frm2.show();
frm2.pictureBox1.Image = "MyImage";
Form3 may refer to the class. You need to use an object to access picturebox1 (or make the field static)
I'm trying to change a listbox in my main form from another file (nodes.cs) which contains another class. I created a class in my main form that changes the textbox for me so all I need to do it pass the string to it. Unfortunately, I can't access the function from the other class unless I make the String-changing-class static. If I make it static, I can't change the listbox without getting an error:
An object reference is required for the non-static field, method, or property...
I know this means I need to create the object or make it non-static. I find the whole class thing rather confusing. I have to initiate a whole new form object to access it? Anyways.
How do I go about accessing a Listbox from another Class, contained in another file? The two classes are in the same namespace.
there's no real point in adding what I have, it's a huge amount of code, and i erased everything I've tried already...
MAIN.CS
namespace neuralnetwork
{
public partial class mainform : Form
{
yada yada
public static void changetext(string text)
{
listbox1.items.add(text);
}
}
}
Secondary.cs
namespace neuralnetwork
{
class lolercopter
{
public static void dolol()
{
//here is where I want to change the mainforms textbox.
mainform.changetext(s);
}
}
}
This is essentially what I have. I've been reading for over an hour on this...
You can pass a reference to mainform into your method:
public static void dolol(mainform frm)
{
frm.changetext(s);
}
Your question leads me to suspect that you have some serious architecture issues with this application, but hopefully this solution can work for you.
classes are like blueprints.
What you're asking is like asking how to open the door down the hall on the blueprint.
It sounds like you want action on one form to trigger action or changed state on another form. That could be achieved by storing state in a database, or in memory, but ideally by having a reference to the instantiated mainform.
How is your nodes class created? Is it created by the form? If so, you could pass in a reference to the form when you create the nodes class.
For example, say you have this code in a callback in the form.
var nodes = new Nodes();
nodes.UpdateSomething( args );
You could change the constructor for the Nodes class so that it takes a reference to form. This is called Dependency Injection, specifically constructor injection. Your class has a dependency on the form, you provide the form when you create the class.
var nodes = new Nodes( this ); // "this" is a reference to the form
nodes.UpdateSomething( args );
Your Nodes class would then use the helper as:
public class Nodes
{
private Form TheForm { get; set; }
public Nodes( Form form )
{
this.TheForm = form;
}
public void UpdateSomething( EventArgs args )
{
...
this.Form.ChangeText( newValue );
...
}
}
The basic idea is to provide the class the resources that it needs access to via the constructor so you don't have to make use of long-lived object references and static classes.
EDIT: I've updated this to reflect your code sample. Note that you're not providing a new class in the form to change the list box, but rather a method.