Method to check which Radio button is checked always returns null

Question

1.00/5 (1 vote)

See more:

So I have a method in my Form class to check which RadioButtons in a GroupBox are selected, and thus return a string.

I then create an instance of Form in another class like this

C#

Form1 form = new Form1();

I then use that object to call my method from the form class

C#

form.whatChecked();

This is my method in the form class

C#

public String whatChecked()
        {
            if (a1.Checked)
            {
                return "a1";
            }
            else if (a2.Checked)
            {
                return "a2";
            }
            else if (a2.Checked)
            {
                return "a3";
            }
            else if (a2.Checked)
            {
                return "a4";
            }
            else if (a2.Checked)
            {
                return "a5";
            }
            else if (a2.Checked)
            {
                return "a6";
            }
            else
            {
                return null;
            }
        }

I've made a check in the other class, and I see that it always returns the "else" value (In this case, Null). I've tested to make sure by having the else return a String, and it does indeed return, even though a1 or a2 are checked.

Posted 22-Aug-15 8:35am

Ridwan Sameer

Add a Solution

Comments

Philippe Mori 23-Aug-15 21:22pm

You should represent your options with an enum. It will be a more maintainable design. Ideally you would also have the mapping between the control and the enumeration value at only once place. That way, if you add options, you only have to do a few localized modifications.

2 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Wendelius · Answer 1 · 2015-08-22T08:41:00

Solution 1

You seem to check the same radio button in most of the cases. Should the code look like:

C#

public String whatChecked()
        {
            if (a1.Checked)
            {
                return "a1";
            }
            else if (a2.Checked)
            {
                return "a2";
            }
            else if (a3.Checked)
            {
                return "a3";
            }
            else if (a4.Checked)
            {
                return "a4";
            }
            else if (a5.Checked)
            {
                return "a5";
            }
            else if (a6.Checked)
            {
                return "a6";
            }
            else
            {
                return null;
            }
        }

ADDED:

C#

private void radioButtons_CheckedChanged(Object sender, EventArgs e)
{
   if (a1.Checked))
   {
      // here execute the code what needs to be done when a1 is selected
      // in the same event handler also add code for other radio buttons since 
      // this event handler will be used for all radio buttons
   }
}

And in the Form_Load event or constructor, wire all the check boxes to use the same event handler

C#

this.a1.CheckedChanged += new System.EventHandler(this.radioButtons_CheckedChanged);
this.a2.CheckedChanged += new System.EventHandler(this.radioButtons_CheckedChanged);
this.a3.CheckedChanged += new System.EventHandler(this.radioButtons_CheckedChanged);
this.a4.CheckedChanged += new System.EventHandler(this.radioButtons_CheckedChanged);
...

Posted 22-Aug-15 8:41am

Wendelius

Updated 22-Aug-15 20:15pm

v2

Comments

Ridwan Sameer 22-Aug-15 14:48pm

Hi, Terribly sorry I had copy pasted an old code.

Yes the code should look like that. However it still does not work

In my other class I call the method and have a check like this

Form1 form = new Form();
parkingspot = form.whatChecked();
if (String.Equals(parkingspot,"a1")){
colour = Color.Gray;
}

Basically, I have a program that prints a moving rectangle of a specific color. So I want it to be such that if a1 is checked, the color will be Gray. However it does not work, but if I changed the else statement in the whatChecked() method to return "a1" it does work, which proves that the method only returns from the else statement, even if a radiobutton is checked.

Wendelius 22-Aug-15 15:05pm

OK I see, but if the method returns say "a5", how do you handle that? Based on the code fragment you only change the color in case of "a1".

Ridwan Sameer 22-Aug-15 15:15pm

Yes, in this specific case I just set it to handle a1 to sort of test out an idea I plan to flesh out later.

I need to be able to get the value of the RadioButton into my current class from the Form Class to build upon my idea. So I basically set it to change the color to Gray if a1 is selected to see if it works.

Ralf Meier 22-Aug-15 16:35pm

Based on which Event do you call the Method (whatChecked) ?
I would prefer to connect the Event CheckedChanged to each Radiobutton and after this you only have to identify the sender ...

Ridwan Sameer 22-Aug-15 23:34pm

I'm sorry I don't exactly get what you mean.
I don't call the method based on an event. I just call it to return a strong based on what is checked, making use of the "radiobutton.Checked()" method, which I was informed would return true or false based on whether it was checked or not.

I read about this checkedChanged event, currently all my checkedChanged events are empty. Could you provide some snippets based on this scenario as to how I could implement it?

Wendelius 23-Aug-15 2:16am

SO do I understand correctly that you call this only once, when the form is loaded? If that is correct, you need to define event handlers which react whenever the state of the checked is changed. Have a look at the updated solution.

Ridwan Sameer 23-Aug-15 2:45am

I get the following error when attempting to run the program

An unhandled exception of type 'System.NullReferenceException' occurred in Parking sim.exe

The line of code which produces the error is

this.a1.CheckedChanged += new System.EventHandler(this.radioButtons_CheckedChanged);

Wendelius 23-Aug-15 2:59am

Probably a1 hasn't been created yet. This happens for example if you place the code before InitializeComponent.

I think the safes place is Window_Loaded so open the window in the designer and add an event handler for the Loaded event.

Ridwan Sameer 23-Aug-15 3:36am

Hi, While waiting for your reply, I actually found a small workaround.

I passed my radio button(s) as a parameter when instantiating an object of the class I was trying to access the radio buttons from. I then used it within the class to get the Checked value and it seems to work.

Is this bad code design? Or is it accepted?

Thanks for all the help Mika!

Wendelius 23-Aug-15 3:39am

Good that you found a solution. However, do you mean that the radio buttons are on another form as your code. If this is the case, then the two forms shouldn't communicate directly. Otherwise you introduce a dependency which may be hard to handle in future.

For example, have a look at Passing Data between Windows Forms[^]

Ridwan Sameer 23-Aug-15 3:56am

Practically, Yes. The RadioButtons are in the "Form" class. I pass those RadioButtons into my drawRectangle class. Which is a custom made class which draws a rectangle.

So I pass it as a parameter

drawRectangle p1 = new drawRectangle (RadioButton a1);
(there are more parameters than this, I'm just doing this to show you what I've done.)

Then in the drawRectangle class I get the information from the constructor

this.a1 = a1;

I then check within the drawRectangle Class

if (a1.Checked) {
colour = Color.Gray;
}

And it works!
It may cause a dependency, but I don't foresee a clash with the way my program is going to be going.

Would your checkedChanged solution that you posted provide me with the same outcome without a dependency? I may have to try it again in that case.

Wendelius 23-Aug-15 6:35am

The solution I posted handles on what happens inside the form when the checked value is changed. How communication between separate classes is done is a whole different story.

If the drawRectangle class doesn't directly use objects from the form but only gets them as parameters the I'd say it's ok.

Ralf Meier 23-Aug-15 14:31pm

You could modify the suggestion from Mika :
The sender from the Eventhandler gives you the Control which changes. Perhaps this is a soltion too for you.
In this case you only have to cast the sender to a Radiobutton. See my solution for this (2).

Philippe Mori 23-Aug-15 21:19pm

It seems that you are creating a new form instead of getting values from the already created form... In which case you will indeed always get null since no radio buttons would initially be checked.

Ralf Meier · Answer 2 · 2015-08-23T08:34:00

This code I have taken from the posted Solution from Mika to change it a little bit (I hope you will forgive me Mika).

C#

private void radioButtons_CheckedChanged(Object sender, EventArgs e)
{
   RadioButton mySender = sender ;
   if (mySender.Checked) && (mySender.Name="A1")
   {
      // here execute the code what needs to be done when a1 is selected
      // in the same event handler also add code for other radio buttons since 
      // this event handler will be used for all radio buttons
   }
}

this could also look like this :

C#

private void radioButtons_CheckedChanged(Object sender, EventArgs e)
{
	if (! object.ReferenceEquals(Sender.gettype, typeof(radiobutton))) return;  // if incomming object is not radiobutton


radiobutton mySender = Sender;
if (mySender.Checked) 
   {

   switch (mySender.name) {
	case "a1":
                // do the Action here
		break;
	case "a2":
                // do the Action here
		break;
      }
   }
}