I have a user control that has a contextmenustrip that is displayed on every right click. When the user select an item on this menu, I have to pass this info to the parent control so it can react according to this.
So I need the parent to mandatory subscribe to this event. Is there a way to tell that?
If there is no way to do that, should I throw an exception or just check for null value (of the event handler) and do nothing?
Thanks.
There is no way to enforce this at compile time - meaning that there is nothing in the .NET framework/C# language that can perform static checks at compilation to ensure that this logic is implemented in your code.
At run-time you can perform the necessary validation. For instance you might inspect the invocation list of the delegate to ensure that the parent is in that list.
You can create a specific constructor for your user control to prevent instantiation unless an event handler is given, like this.
public partial class MyUserControl : UserControl {
public MyUserControl (ToolStripItemClickedEventHandler handler) {
InitializeComponent ();
myContextMenuStrip.ItemClicked += handler;
}
}
Do note though: this won't work very well with Visual Studio's form designer, as the form designer generally expects parameter-less constructors. Instead, you need to manually create the control instance from code.
Related
I have a relatively simple setup. I have a custom usercontrol that has a bunch of components on it, some text boxes, and a listview.
In the designer, I can drag and drop other controls into my usercontrol, and it adds them to the usercontrol instance. I don't want this.
How can I explicitly say "Don't allow additional controls to be added to this usercontrol?"
That's not the way it works. When you drop your user control on a form then adding controls to it isn't supported. That requires a special designer, this answer shows what is required. Maybe it looks like the controls get added but they merely overlap your user control. Their parent is still the form.
If a programmer opens your user control class itself in the designer then, sure, he can add controls as he pleases. The only way to stop that is to not ship the source code and use the sealed keyword to prevent deriving from it.
You could create a boolean property MyContainer.DisableAddControls or something.
If your MyContainer.Controls.Add(..) is overridden, then you can throw some custom exception in that Add() method as follows:
if(DisableAddControls)
{
throw new DisableAddControlsException();
}
If you are inheriting that method straight from ContainerControl, then you can handle the ControlAdded event and throw the exception there.
myContainer.ControlAdded += myContainerControlAdded;
private void Control_Added(object sender, System.Windows.Forms.ControlEventArgs e)
{
if(DisableAddControls)
{
throw new DisableAddControlsException();
}
}
On second thought, this won't throw out your designer at design time... nevermind.
I created a user control with an event. I do not want to add the following code every time I add a new instance of the control to a form.
Control1.Operate += new MyControl.OperateEventHandler(Control1_Operate)
Instead I would like to simply double-click the control and have the above code added by the IDE to the Designer file. By default the Control1_Load event is assigned in the Designer file. Is it possible to change this?
For C# use:
[DefaultEvent("Click")]
public class MyClass : BaseClass
{
//code
}
MS Code:
http://msdn.microsoft.com/en-us/library/system.componentmodel.defaulteventattribute.aspx
It seems you want to set a DefaultEvent for your control.
Use DefaultEventAttribute on your Control class.
A similar question exists:
How can I set the default event to be edited for my custom control in Visual Studio?
Hope it helps!
The behavior you are looking for is more like what you have for buttons. You double click on it and you have the event handler method generated for you. But in here, the event handler code is generated on the fly. In your cae, you want to attach, a pre-defined method with the event of the User Control. Try defining some custom properties or event for your usercontrol and then set the default value. For e.g. : http://msdn.microsoft.com/en-us/library/yhzc935f.aspx .
Currently I have a C# program with a windows form and then a user control template put onto the form. The user control template is really just used as a placeholder. I have a series of other controls which inherit from this user control template.
Each of those controls have navigation buttons like 'Continue' and 'Back' on them and each control knows which control needs to be loaded next. However what I need to figure out is an easier way to have variables that are global to these controls.
The only workaround I have is that I pass the form to each control when they are loaded and use variables inside of the form to read and write to. What would be the proper way to have each of these user control screens be built off of a base control which contained objects all of the controls could get to?
Sorry for the rambling nature of the post but I've been thinking about this problem all morning.
Here is some of the code:
Most of what I have written was based on hiding and showing the user controls so that content in the controls wouldn't be lost during navigation. I won't be needing to do that as eventually it will be loading the fields of data from a database.
Code for initially loading control from form click:
conTemplate1.Controls.Clear();
conInbound Inbound = new conInbound(this);
Inbound.Dock = DockStyle.Fill;
Inbound.Anchor = (AnchorStyles.Left | AnchorStyles.Top);
conTemplate1.Controls.Add(Inbound);
Code for Continue button inside of one of the controls:
if ((Parent.Controls.Count - 1) <= Parent.Controls.IndexOf(this))
{
UserControl nextControl = new conPartialClear();
nextControl.Dock = DockStyle.Fill;
Parent.Controls.Add(nextControl);
this.Hide();
Parent.Controls[Parent.Controls.IndexOf(this) + 1].Show();
}
else
{
this.Hide();
Parent.Controls[Parent.Controls.IndexOf(this) + 1].Show();
}
The best-practice for communicating from a control to a parent is to use events, and for communicating from a parent to a control is to call methods.
However, if you don't want to or can't follow this practice, here's what I would recommend.
Each UserControl has a ParentForm property that returns the Form that contains the control. If you know that the UserControl will always be attached to MyParentForm, you just cast the ParentForm and then you can access all public controls, methods, etc.
Here's what I mean:
public class conTemplate
{
public MyParentForm MyParentForm
{
get
{
return (MyParentForm)this.ParentForm;
}
}
}
This way, you can easily access any public members of MyParentForm. Your conInbound class could have code such as this.MyParentForm.GlobalSettings.etc..., and could even have access to any public controls.
I'm not totally sure I understand your problem. It sounds like you want the user control to "do something" with it's parent form. If that's the case, you may want to consider adding events to the UC and then handle them on the form itself.
Basically, for your UC's "continue", you'll have an event that's fired when it's pressed. You'll want to handle that in your form. I'm not real sure about the syntax from memory, or I'd work something out for you code-wise. But I think that's the route you'll want to take. Think of your UC like any other windows form control. If you add a button to your form, you assign it it's event method. Do the same with the UC.
I found this and thought it may be helpful. Scroll down to where it talks about UC's and events.
http://www.akadia.com/services/dotnet_user_controls.html
Hope this helps.
EDIT after new info from OP.
You could declare a global variable inside the UC of type yourForm and then set that variable to the ParentForm at run-time, if I'm understanding you correctly.
So, inside your UC Class, you could do:
private parentFormInstance;
then inside the constructor of the UC, you could set it as such:
parentFormInstance = this.ParentForm; (or whatever the property name is).
This allows you at design-time to use:
parentFormInstance.DoSomething();
without the compiler yelling at you.
Just basic advice, but if you can go back and make it easier on yourself, even if it takes some additional time re-working things, it'd be worth it. It may save you time in the long run.
I have a parent control (main form) and a child control (user control). The child control has some code, which determines what functions the application can perform (e.g. save files, write logs etc.). I need to show/hide, enable/disable main menu items of the main form according to the functionality. As I can't just write MainMenu.MenuItem1.Visible = false; (the main menu is not visible from the child control), I fire an event in the child control and handle this event on the main form. The problem is I need to pass what elements of the menu need to be shown/hidden. To do this I created an enum, showing what to do with the item
public enum ItemMode
{
TRUE, FALSE, NONE
}
Then I created my eventargs which have 6 parameters of type ItemMode (there are 6 menu items I need to manage). So any time I need to show the 1st item, hide the 2nd and do nothing with the rest I have to write something like this
e = new ItemModeEventArgs(ItemMode.TRUE, ItemMode.FALSE, ItemMode.NONE, ItemMode.NONE, ItemMode.NONE, ItemMode.NONE);
FireMyEvent(e);
This seems like too much code to me and what's more, what if I need to manage 10 items in future? Then I will have to rewrite all the constructors just to add 4 more NONEs.
I believe there's a better way of doing this, but I just can't figure out what it is.
you could create an EventArgs which takes an ItemMode[] or a List<ItemMode> or a Dictionary<string, ItemMode> for those items (instead of the current 6 arguments) - that way you don't need to change much when adding more items...
The chain child->parent can be reversed. In such scenario requests will be passed from the mainform to its child controls.
Controls participating in the command processing must implement a special interface:
interface ICommandHandler
{
bool CanInvoke(int commandId);
void InvokeCommand(int commandId);
bool UpdateCommand(int commandId, MenuItem item);
}
The advantage of this approach is that only active controls must be traversed, not all the children.
The weak point - UpdateCommand() method, which could be called from Application.Idle event or timer.
hope this helps
Well, I can't speak to a "best" way unless except in specific cases, since there are often several equally good ways. My first thought, though, would be to create a class that has a property which the parent assigns a reference of its MainMenu, and which has functions for enabling/disabling individual menus or items. In a very simple case, this could be as simple as passing a list of strings like "OptionsScreen=enabled" etc. and then inside the class manually handling those cases, to something more generic like passing strings such as "mnuToolsOptions=enabled" and then finding the menu item via the .Name property. So, on startup, create an instance of your menu handler class, then do something like MenuHandlerHelper.MenuToHandle = MainMenuStrip;.
On the child side, you could perhaps have your classes that update the MainMenu be derived UserObjects that derive from a common one you create that has a public MyMainMenuHandlerHelper MenuHandlerHelper property, and set that in your Parent form's constructor so the Child controls could call the menu updating function. Or, you could have an event that just passed back a List<string> containing all the rules, and fire that as you are doing now.
This is a very simple idea, and doesn't handle things like possible collisions, so you would probably either want to throw an exception (easiest). You might also want to have rule priorities (easy), or try to chain functionality (could be hard to determine orders and such).
I would be happy to implement some examples of my thinking if you can constrain the problem a little for me (desired collision handling, etc.) and I actually wanted to see what some basic code would look like and try perhaps to test a couple of ideas, so if those come to anything I will post the code here for those as well.
If you want to handle all changes from the user control: you could inherit your own user control class and add a reference to the form/collection of menu entries you want to be able to modify. You would pass this reference to its constructor and then you'll be able to easily modify the menu from inside your user control
If, on the other hand, you would like to manage this on an event basis in your form, you could implement your own EventArgs class, but I would do it like this:
class ItemModeEventArgs
{
MenuItemClass target;
EnumType change;
}
So basically for each menu item a separate event is risen. Every event args knows about what item menu is changing and how it is changing. Ofc, if you only have two states for the menu items, the 'change' field is kinda useless.
This way you don't have to hardcode functions with n parameters where n is the number of menu items.
There truly are many ways this could be done. The easiest way, although some will shout "bad practice", would be to just pass a pointer to the main menu when the control is created. Your control would have some code like this:
MenuStrip MainMenu;
internal void SetMainMenu(MenuStrip mainMenu)
{
MainMenu = mainMenu;
}
and when you create the control:
void CreateControl()
{
MyUserControlType MyControl = new MyUserControlType();
MyControl.SetMainMenu(mainMenuStrip); //or whatever you called your main menu
}
This will give your child form unlimited access to the mainform's menu (which is why it's technically a bad practice). From the child form you can access the submenus by name, eg:
if (MainMenu != null)
{
ToolStripMenuItem fileMenu =
(ToolStripMenuItem)MainMenu.Items["fileToolStripMenuItem"];
fileMenu.DropDownItems["exportFileToolStripItem"].Visible = false;
}
If you created the control in the designer, then you can add the SetMainMenu call into the .design file, or add it in the Form's load event.
i want to fire an event manually using c#. For instance, say if i want to fire a Form_closing event of Form A from Form B. How to do it ??
After getting some comments. I think i need to explain more on this.
Since my Form A is reference to a .dll which creates a custom taskbar in the desktop,
There is a situation for me to close the that custom taskbar from Form B.
i already tried FormA.Close() from Form B. when i do this, the .dll is unloaded from the app domain and due to this the space occupied by the custom task bar is blocked.
But that is not the case when i click the close button in the custom task bar. when i do this the space is freed up.
This is the reason i want to fire the close event of Form A manually from Form B which will solve my issue.
Thanks.
We did the following in one project:
There was a GlobalNotifier class, which defined events we wanted to use in different modules of the application, like this
public static class GlobalNotifier
{
public static event VoidEventHandler EnvironmentChanged;
public static void OnEnvironmentChanged()
{
if (EnvironmentChanged != null)
{
EnvironmentChanged();
}
}
}
Then, you could raise this event anywhere when you needed to let the rest of the application know that the environment has changed, like this
GlobalNotifier.OnEnvironmentChanged();
And also you could subscribe to this event wherever you wanted to be notified about the fact that the environment has changed.
public ReportingService()
{
GlobalNotifier.EnvironmentChanged += new VoidEventHandler(GlobalNotifier_EnvironmentChanged);
}
void GlobalNotifier_EnvironmentChanged()
{
//reset settings
_reportSettings = null;
}
So, whenever you changed the environment, you raised the event, and everyone who needed to know about that and perform some actions, was notified.
Might be similar to what you need to achieve.
Also, if you need to pass parameters, you can define the event any way you like, basically -
public static event VoidEventHandler<SomeObject, List<OtherObject>> SomethingUpdated;
public static void OnSomethingUpdated(SomeObject sender, List<OtherObject> associations)
{
if (SomethingUpdated != null)
{
SomethingUpdated(sender, associations);
}
}
// ...
MyClass.SomethingUpdated+= new VoidEventHandler<SomeObject, List<OtherObject>>(MyClass_SomethingUpdated);
// ...
void MyClass_SomethingUpdated(SomeObject param1, List<OtherObject> param2)
{
//do something
}
You would call the OnFormClosing() method of the Form class. You can do this with any event that has a paired On...() method.
It sounds to me, from your comments, like you don't want to raise one form's event from the other; you just want to handle one form's event from the other.
Yes, you can do that. FormB needs to have a reference to FormA. There are several ways you can do this; one easy way is to have a FormA type property in your FormB class, like this:
public FormA TheOtherForm { get; set; }
You set that property to your instance of FormA, and then you add the event handler as you've described in the comments.
You don't have to use FormA as the type of your property; any form has the FormClosing event, so you can just use Form as the type if you want.
Close the form. That will raise the event. If you want to raise the event separately from closing the form, you're doing something wrong; move that code to a separate method that you can call from the event and from FormB.
FormAInstance.Close()
Starting with Visual Studio 2005 (.Net 2.0), forms have automatic default instances. It sounds like that's what you're using. You should know that this feature exists mainly for backwards compatibility with VB6. You're really better off creating and using a new instance of the form. When you do that, you should just be able to call the .Close() method on that instance without it's app domain closing.
If you want to re-use this space, you might also try simply .Hide()-ing the form rather than closing it.