Best way to access a control on another form in Windows Forms

Question

First off  this is a question about a desktop application using Windows Forms  not an ASP NET question   I need to interact with controls on other forms  I am trying to access the controls by using  for example  the following     otherForm Controls  nameOfControl   Visible   false    It doesn t work the way I would expect  I end up with an exception thrown from Main  However  if I make the controls public instead of private  I can then access them directly  as so     otherForm nameOfControl Visible   false    But is that the best way to do it  Is making the controls public on the other form considered  best practice   Is there a  better  way to access controls on another form   Further Explanation   This is actually a sort of follow-up to another question I asked  Best method for creating a    tree-view preferences dialog    type of interface in C    The answer I got was great and solved many  many organizational problems I was having in terms of keeping the UI straight and easy to work with both in run-time and design-time  However  it did bring up this one niggling issue of easily controlling other aspects of the interface   Basically  I have a root form that instantiates a lot of other forms that sit in a panel on the root form  So  for instance  a radio button on one of those sub-forms might need to alter the state of a status strip icon on the main  root form  In that case  I need the sub-form to talk to the control in the status strip of the parent  root  form   I hope that makes sense  not in a  who s on first  kind of way

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Change modifier from public to internal   Net deliberately uses private modifier instead of the public  due to preventing any illegal access to your methods properties controls out of your project  In fact  public modifier can accessible wherever  so They are really dangerous  Any body out of your project can access to your methods properties  But In internal modifier no body  other of your current project  can access to your methods properties   Suppose you are creating a project  which has some secret fields  So If these fields being accessible out of your project  it can be dangerous  and against to  your initial ideas  As one good recommendation  I can say always use internal modifier instead of public modifier   But some strange   I must tell also in VB Net while our methods properties are still private  it can be accessible from other forms class by calling form as a variable with no any problem else    I don t know why in this programming language behavior is different from C   As we know both are using same Platform and they claim they are almost same Back end Platform  but as you see  they still behave differently   But I ve solved this problem with two approaches  Either  by using Interface  Which is not a recommend  as you know  Interfaces usually need public modifier  and using a public modifier is not recommend  As I told you above      Or   Declare your whole Form in somewhere static class and static variable and there is still internal modifier  Then when you suppose to use that form for showing to users  so pass new Form   construction to that static class variable  Now It can be Accessible every where as you wish  But you still need some thing more   You declare your element internal modifier too in Designer File of Form  While your Form is open  it can be accessible everywhere  It can work for you very well   Consider This Example   Suppose you want to access to a Form s TextBox    So the first job is declaration of a static variable in a static class  The reason of static is ease of access without any using new keywork at future     Second go to designer class of that Form which supposes to be accessed by other Forms  Change its TextBox modifier declaration from private to internal  Don t worry   Net never change it again to private modifier after your changing   Third when you want to call that form to open  so pass the new Form Construction  to that static variable--  static class   Fourth   from any other Forms  wherever in your project  you can access to that form control while From is open   Look at code below  We have three object   1- a static class  in our example we name it A    2 - Any Form else which wants to open the final Form  has TextBox  in our example FormB     3 - The real Form which we need to be opened  and we suppose to access to its internal TextBox1  in our example FormC     Look at codes below   internal static class A       internal static FormC FrmC     FormB                      A FrmC   new FormC                  FormC  Designer File                internal System Windows Forms TextBox TextBox1      You can access to that static Variable  here FormC  and its internal control  here Textbox1  wherever and whenever as you wish  while FormC is open     Any Comment idea let me know  I glad to hear from you or any body else about this topic more  Honestly I have had some problems regard to this mentioned problem in past  The best way was the second solution that I hope it can work for you   Let me know any new idea suggestion

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With the property  highlighted  I can get the instance of the MainForm class  But this is a good practice  What do you recommend    For this I use the property MainFormInstance that runs on the OnLoad method   using System  using System Collections Generic  using System ComponentModel  using System Data  using System Drawing  using System Linq  using System Text  using System Windows Forms  using LightInfocon Data LightBaseProvider  using System Configuration   namespace SINJRectifier        public partial class MainForm   Form               public MainForm                         InitializeComponent                       protected override void OnLoad EventArgs e                        UserInterface userInterfaceObj   new UserInterface                this chklbBasesList Items AddRange userInterfaceObj ExtentsList this chklbBasesList                MainFormInstance MainFormInstanceSet   this    Here I get the instance                    private void btnBegin Click object sender  EventArgs e                        Maestro ConductSymphony                ErrorHandling SetExcecutionIsAllow                         static class MainFormInstance    Here I get the instance               private static MainForm mainFormInstance           public static MainForm MainFormInstanceSet   set   mainFormInstance   value               public static MainForm MainFormInstanceGet   get   return mainFormInstance

User · Answer

Use an event handler to notify other the form to handle it  Create a public property on the child form and access it from parent form  with a valid cast   Create another constructor on the child form for setting form s initialization parameters Create custom events and or use  static  classes    The best practice would be  4 if you are using non-modal forms

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This looks like a prime candidate for separating the presentation from the data model   In this case  your preferences should be stored in a separate class that fires event updates whenever a particular property changes  look into INotifyPropertyChanged if your properties are a discrete set  or into a single event if they are more free-form text-based keys    In your tree view  you ll make the changes to your preferences model  it will then fire an event   In your other forms  you ll subscribe to the changes that you re interested in   In the event handler you use to subscribe to the property changes  you use this InvokeRequired to see if you are on the right thread to make the UI call  if not  then use this BeginInvoke to call the desired method to update the form

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I personally would recommend NOT doing it    If it s responding to some sort of action and it needs to change its appearance  I would prefer raising an event and letting it sort itself out     This kind of coupling between forms always makes me nervous  I always try to keep the UI as light and independent as possible    I hope this helps  Perhaps you could expand on the scenario if not

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I would handle this in the parent form   You can notify the other form that it needs to modify itself through an event

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You should only ever access one view s contents from another if you re creating more complex controls modules components   Otherwise  you should do this through the standard Model-View-Controller architecture   You should connect the enabled state of the controls you care about to some model-level predicate that supplies the right information   For example  if I wanted to enable a Save button only when all required information was entered  I d have a predicate method that tells when the model objects representing that form are in a state that can be saved   Then in the context where I m choosing whether to enable the button  I d just use the result of that method   This results in a much cleaner separation of business logic from presentation logic  allowing both of them to evolve more independently     letting you create one front-end with multiple back-ends  or multiple front-ends with a single back-end with ease   It will also be much  much easier to write unit and acceptance tests for  because you can follow a  Trust But Verify  pattern in doing so    You can write one set of tests that set up your model objects in various ways and check that the  is savable  predicate returns an appropriate result  You can write a separate set of that check whether your Save button is connected in an appropriate fashion to the  is savable  predicate  whatever that is for your framework  in Cocoa on Mac OS X this would often be through a binding     As long as both sets of tests are passing  you can be confident that your user interface will work the way you want it to

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You can   Create a public method with needed parameter on child form and call it from parent form  with valid cast  Create a public property on child form and access it from parent form  with valid cast  Create another constructor on child form for setting form s initialization parameters Create custom events and or use  static  classes   Best practice would be  4 if you are using non-modal forms

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Suppose you have two forms  and you want to hide the property of one form via another   form1 ob   new form1    ob Show this   this Enabled  false    and when you want to get focus back of form1 via form2 button then   Form1 ob   new Form1    ob Visible   true  this Close

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Lars  good call on the passing around of Form references  seen it as well myself  Nasty  Never seen them passed them down to the BLL layer though  That doesn t even make sense  That could have seriously impacted performance right  If somewhere in the BLL the reference was kept  the form would stay in memory right   You have my sympathy         Ed  RE your comment about making the Forms UserControls  Dylan has already pointed out that the root form instantiates many child forms  giving the impression of an MDI application  where I am assuming users may want to close various Forms   If I am correct in this assumption  I would think they would be best kept as forms  Certainly open to correction though

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Instead of making the control public  you can create a property that controls its visibility   public bool ControlIsVisible        get   return control Visible         set   control Visible   value        This creates a proper accessor to that control that won t expose the control s whole set of properties

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I agree with using events for this  Since I suspect that you re building an MDI-application  since you create many child forms  and creates windows dynamically and might not know when to unsubscribe from events  I would recommend that you take a look at Weak Event Patterns  Alas  this is only available for framework 3 0 and 3 5 but something similar can be implemented fairly easy with weak references   However  if you want to find a control in a form based on the form s reference  it s not enough to simply look at the form s control collection  Since every control have it s own control collection  you will have to recurse through them all to find a specific control  You can do this with these two methods  which can be improved    public static Control FindControl Form form  string name        foreach  Control control in form Controls                Control result   FindControl form  control  name            if  result    null              return result             return null     private static Control FindControl Form form  Control control  string name        if  control Name    name            return control             foreach  Control subControl in control Controls                Control result   FindControl form  subControl  name            if  result    null              return result             return null

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The first is not working of course  The controls on a form are private  visible only for that form by design   To make it all public is also not the best way   If I would like to expose something to the outer world  which also can mean an another form   I make a public property for it   public Boolean nameOfControlVisible       get   return this nameOfControl Visible        set   this nameOfControl Visible   value        You can use this public property to hide or show the control or to ask the control current visibility property   otherForm nameOfControlVisible   true    You can also expose full controls  but I think it is too much  you should make visible only the properties you really want to use from outside the current form   public ControlType nameOfControlP       get   return this nameOfControl        set   this nameOfControl   value

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public void Enable Usercontrol1         UserControl1 usercontrol1   new UserControl1        usercontrol1 Enabled   true            Put this Anywhere in your Form and Call it by Enable Usercontrol1        Also  Make sure the Usercontrol1 Modifiers is Set to Protected Internal

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Do your child forms really need to be Forms   Could they be user controls instead   This way  they could easily raise events for the main form to handle and you could better encapsulate their logic into a single class  at least  logically  they are after all classes already     Lars   You are right here   This was something I did in my very beginning days and have not had to do it since  that is why I first suggested raising an event  but my other method would really break any semblance of encapsulation    Rob  Yup  sounds about right      0 2 on this one

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After reading the additional details  I agree with robcthegeek  raise an event  Create a custom EventArgs and pass the neccessary parameters through it

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