Call me crazy, but I'm the type of guy that likes constructors with parameters (if needed), as opposed to a constructor with no parameters followed by setting properties. My thought process: if the properties are required to actually construct the object, they should go in the constructor. I get two advantages:
I know that when an object is constructed (without error/exception), my object is good.
It helps avoid forgetting to set a certain property.
This mindset is starting to hurt me in regards to form/usercontrol development. Imagine this UserControl:
public partial class MyUserControl : UserControl
{
public MyUserControl(int parm1, string parm2)
{
// We'll do something with the parms, I promise
InitializeComponent();
}
}
At designtime, if I drop this UserControl on a form, I get an Exception:
Failed to create component 'MyUserControl' ...
System.MissingMethodException - No parameterless constructor defined for this object.
It seems like, to me, the only way around that was to add the default constructor (unless someone else knows a way).
public partial class MyUserControl : UserControl
{
public MyUserControl()
{
InitializeComponent();
}
public MyUserControl(int parm1, string parm2)
{
// We'll do something with the parms, I promise
InitializeComponent();
}
}
The whole point of not including the parameterless constructor was to avoid using it. And I can't even use the DesignMode property to do something like:
public partial class MyUserControl : UserControl
{
public MyUserControl()
{
if (this.DesignMode)
{
InitializeComponent();
return;
}
throw new Exception("Use constructor with parameters");
}
}
This doesn't work either:
if (LicenseManager.UsageMode == LicenseUsageMode.Designtime)
Fine, moving along ...
I have my parameterless constructor, I can drop it on the form, and the form's InitializeComponent will look like this:
private void InitializeComponent()
{
this.myControl1 = new MyControl();
// blah, blah
}
And trust me, because I did it (yes, ignoring the comments Visual Studio generated), I tried messing around and I passed parameters to InitializeComponent so that I could pass them to the constructor of MyControl.
Which leads me to this:
public MyForm()
{
InitializeComponent(); // Constructed once with no parameters
// Constructed a second time, what I really want
this.myControl1 = new MyControl(anInt, aString);
}
For me to use a UserControl with parameters to the constructor, I have to add a second constructor that I don't need? And instantiate the control twice?
I feel like I must be doing something wrong. Thoughts? Opinions? Assurance (hopefully)?
Design decisions made regarding the way Windows Forms works more or less preclude parameterized .ctors for windows forms components. You can use them, but when you do you're stepping outside the generally approved mechanisms. Rather, Windows Forms prefers initialization of values via properties. This is a valid design technique, if not widely used.
This has some benefits, though.
Ease of use for clients. Client code doesn't need to track down a bunch of data, it can immediately create something and just see it with sensible (if uninteresting) results.
Ease of use for the designer. Designer code is clearer and easier to parse in general.
Discourages unusual data dependencies within a single component. (Though even microsoft blew this one with the SplitContainer)
There's a lot of support in forms for working properly with the designer in this technique also. Things like DefaultValueAttribute, DesignerSerializationVisibilityAttribute, and BrowsableAttribute give you the opportunity to provide a rich client experience with minimal effort.
(This isn't the only compromise that was made for client experience in windows forms. Abstract base class components can get hairy too.)
I'd suggest sticking with a parameterless constructor and working within the windows forms design principles. If there are real preconditions that your UserControl must enforce, encapsulate them in another class and then assign an instance of that class to your control via a property. This will give a bit better separation of concern as well.
There are two competing paradigms for designing classes:
Use parameterless constructors and set a bunch of properties afterwards
Use parameterized constructors to set properties in the constructor
The Visual Studio Windows Forms Designer forces you to provide a parameterless constuctor on controls in order to work properly. Actually, it only requires a parameterless constructor in order to instantiate controls, but not to design them (the designer will actually parse the InitializeComponent method while designing a control). This means that you can use the designer to design a form or user control without a parameterless constructor, but you cannot design another control to use that control because the designer will fail to instantiate it.
If you don't intend to programmatically instantiate your controls (i.e. build your UI "by hand"), then don't worry about creating parameterized constructors, since they won't be used. Even if you are going to programmatically instantiate your controls, you may want to provide a parameterless constructor so they can still be used in the designer if need be.
Regardless of which paradigm you use, it is also generally a good idea to put lengthy initialization code in the OnLoad() method, especially since the DesignMode property will work at load time, but not work in the constructor.
I would recommend
public partial class MyUserControl : UserControl
{
private int _parm1;
private string _parm2;
private MyUserControl()
{
InitializeComponent();
}
public MyUserControl(int parm1, string parm2) : this()
{
_parm1 = parm1;
_parm2 = parm2;
}
}
As this way the base constructor is always called first and any references to components are valid.
You could then overload the public ctor if need be, ensuring the control is always instantiated with the correct values.
Either way, you ensure that the parameterless ctor is never called.
I haven't tested this so if it falls over I apologise!
This is unfortunately a design issue that will occur frequently, not just in the control space.
There are often situations where you need to have a parameterless constructor, even though a parameterless constructor is not ideal. For example, many value types, IMO, would be better off without parameterless constructors, but it's impossible to create one that works that way.
In these situations, you have to just design the control/component in the best manner possible. Using reasonable (and preferably the most common) default parameters can help dramatically, since you can at least (hopefully) initialize the component with a good value.
Also, try to design the component in a way that you can change these properties after the component is generated. With Windows Forms components, this is typically fine, since you can pretty much do anything until load time safely.
Again, I agree - this isn't ideal, but it's just something we have to live with and work around.
Well, in short, the designer is the kind of guy that likes parameter-less constructors. So, to the best of my knowledge, if you really want to use parameter based constructors you are probably stuck with working around it one way or the other.
Just do this:
public partial class MyUserControl : UserControl
{
public MyUserControl() : this(-1, string.Empty)
{
}
public MyUserControl(int parm1, string parm2)
{
// We'll do something with the parms, I promise
if (parm1 == -1) { ... }
InitializeComponent();
}
}
Then the 'real' constructor can act accordingly.
Provide a parameterless constructor for the designer and make it private - if you really must do it this way... :-)
EDIT: Well of course this won't work for UserControls. I obviously wasn't thinking clearly. The designer need to execute the code in InitializeComponent() and it's can't work if the constructor is private. Sorry about that. It does work for forms, however.
It's quite a while since the question was asked, but maybe my approach is helpful to somebody.
I personally also prefer to use parameterized Constructors to avoid forgetting to set a certain property.
So instead of using the actual Constructor I simply define a public void PostConstructor where all things are put you would normally put in the Constructor. So the Actual Constructor of the UserControl always contains only InitializeComponent().
This way you don't have to adjust your favourite programming paradigm to VisualStudios needs to run the Designer properly. For this programming schema to work it has to be followed from the very bottom.
In practice this PostConstructionalizm would look somewhat like this:
Let's start with a Control at the bottom of your UserControl call hierarchy.
public partial class ChildControl : UserControl
{
public ChildControl()
{
InitializeComponent();
}
public void PostConstructor(YourParameters[])
{
//setting parameters/fillingdata into form
}
}
So a UserControl containing the ChildControl would look something like that:
public partial class FatherControl : UserControl
{
public FatherControl()
{
InitializeComponent();
}
public void PostConstructor(YourParameters[])
{
ChildControl.PostConstructor(YourParameters[])
//setting parameters/fillingdata into form
}
}
And finally a Form calling one of the User Control simply puts the PostConstructor after InitializeComponent.
public partial class UI : Form
{
public UI(yourParameters[])
{
InitializeComponent();
FatherControl.PostConstructor(yourParameters[]);
}
}
I have a way to work around it.
Create a control A on the form with the parameterless constructor.
Create a control B with parameterized constructor in the form contstructor.
Copy position and size from A to B.
Make A invisible.
Add B to A's parent.
Hope this will help. I just encountered the same question and tried and tested this method.
Code for demonstrate:
public Form1()
{
InitializeComponent();
var holder = PositionHolderAlgorithmComboBox;
holder.Visible = false;
fixedKAlgorithmComboBox = new MiCluster.UI.Controls.AlgorithmComboBox(c => c.CanFixK);
fixedKAlgorithmComboBox.Name = "fixedKAlgorithmComboBox";
fixedKAlgorithmComboBox.Location = holder.Location;
fixedKAlgorithmComboBox.Size = new System.Drawing.Size(holder.Width, holder.Height);
holder.Parent.Controls.Add(fixedKAlgorithmComboBox);
}
holder is Control A, fixedKAlgorithmComboBox is Control B.
An even better and complete solution would be to use reflect to copy the properties one by one from A to B. For the time being, I am busy and I am not doing this. Maybe in the future I will come back with the code. But it is not that hard and I believe you can do it yourself.
I had a similar problem trying to pass an object created in the main Windows Form to a custom UserControl form. What worked for me was adding a property with a default value to the UserControl.Designer.cs and updating it after the InitializeComponent() call in the main form. Having a default value prevents WinForms designer from throwing an "Object reference not set to an instance of an object" error.
Example:
// MainForm.cs
public partial class MainForm : Form
public MainForm()
{
/* code for parsing configuration parameters which producs in <myObj> myConfig */
InitializeComponent();
myUserControl1.config = myConfig; // set the config property to myConfig object
}
//myUserControl.Designer.cs
partial class myUserControl
{
/// <summary>
/// Required designer variable.
/// </summary>
private System.ComponentModel.IContainer components = null;
/// <summary>
/// Clean up any resources being used.
/// </summary>
/// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
protected override void Dispose(bool disposing)
{
if (disposing && (components != null))
{
components.Dispose();
}
base.Dispose(disposing);
}
// define the public property to hold the config and give it a default value
private myObj _config = new myObj(param1, param2, ...);
public myObj config
{
get
{
return _config ;
}
set
{
_config = value;
}
}
#region Component Designer generated code
...
}
Hope this helps!
Related
I have a fairly simple application that monitors folder activity and logs it on a server.
In this application I start off with a Form object called Form1. On this form I have a NotifyIcon. Because I need to change the text in the BalloonTip of the NotifyIcon from different Forms along the way, I was thinking of setting a static property of Form1 that will point to the only instance of Form1. This is how it would look in my oppinion:
public partial class Form1 : Form
{
private static Form1 staticRef;
// Other private properties
public Form1()
{
InitializeComponent();
staticRef = this;
// Rest of constructor logic
}
public static void changeNotifyBalloonText(String newText, int timeInMillis)
{
if (staticRef != null && staticRef.notifyIcon1 != null)
{
staticRef.notifyIcon1.BalloonTipText = newText;
staticRef.notifyIcon1.ShowBalloonTip(timeInMillis);
}
}
// Rest of public and private methods
}
Other things to be noted:
a. There will never be more than 1 instance of Form1.
b. I always check the value of staticRef against null, before trying to use it.
c. I cannot afford to make a temporary, local instance of Form1 just to set a BalloonTip message.
d. This solution works very well, i'm more interested in knowing if it's "too hacky" and if so - what would be a better approach to my issue?
e. The closest thing I've found that may answer my question (about static properties) to some degree is here:
Is using a static property in a form bad practice knowing that there's only only one instance of the form?
What you have here is a form of the singleton pattern.
The singleton pattern certainly has its detractors and its defenders (google "singleton anti-pattern").
It is though a very convenient way of doing this.
I would recommend an approach like either::
Create a class that represents operations on a notify icon.
Have that class as the only class that accesses staticRef.notifyIcon1.
Have it do so as a reference to notifyIcon1, not as Form1.
Have a static method or property that gets the icon-controlling class.
Or:
Simply have a static method or property that returns the NotifyIcon object.
Make it the only method that accesses the static reference to the form.
The advantage of one over the other is around whether you want to expose the full interface of NotifyIcon or provide a set of operations that make sense to your application.
This way you are still using the singleton pattern, but in restricting the way that it is accessed the fact that there is global state has less of a global impact, relates more directly to the purpose of that global state (the icon itself), and is more readily extended to different uses. e.g. if you some day need to have two icons, you change the method that static method or property to one that does a lookup of some sort, and change all the current calls to use the key for the first icon. Meanwhile, implementation changes up to and including completely changing which form provides that icon can be done quickly in one place.
I think your current design is tightly coupled to other classes sending the notification and it requires your form to be a single instance as well.
You can decouple this a great deal by using an event broker to send the notification to any interested parties. Many frameworks have event brokers, I have used one from Prism but there are others as well.
Your code will then only know about the event broker and what events your class is interested in.
public partial class Form1 : Form
{
private static IEventBroker eventBroker;
// Other private properties
public Form1(IEventBroker eventBroker)
{
InitializeComponent();
this.eventBroker = eventBroker;
this.eventBroker.Register<NotifyBaloonText>(changeNotifyBalloonText);
}
public static void changeNotifyBalloonText(NotifyBaloonText args)
{
notifyIcon1.BalloonTipText = args.NewText;
notifyIcon1.ShowBalloonTip(args.TimeInMillis);
}
// Rest of public and private methods
}
I'm getting a warning message in Visual Studio 2010 (the one in the title)
Basically I've made a generic form which has a bunch of variables, virtual functions.
It takes a class I made as a parameter and assigns it to a local variable (which is then put as a propety using getters and setters)
I then made another form which inherits from this form. All is well, it runs, but when I attempt to look at the designer of it, I get that error message.
public TAGeneric(TAManager iManager)
{
ControlHelper.SuspendDrawing(this);
mManager = iManager;
SetStyle(ControlStyles.OptimizedDoubleBuffer |
ControlStyles.UserPaint |
ControlStyles.AllPaintingInWmPaint, true);
InitializeComponent();
SetupCommandBar();
ControlHelper.ResumeDrawing(this);
}
Thats the parent.
public TAAddInterval(TAManager iManager) : base(iManager)
{
InitializeComponent();
}
This is a child. Forget the fact I'm using a "manager" when it is frowned upon. Anyone shed some light on the problem? Literally works fine to run, but when it comes to trying to edit the graphical side in designer, It won't load it.
Thanks for the help.
I suspect you need to provide a parameterless constructor for the designer to use:
public TAAddInterval(TAManager iManager) : base(iManager)
{
InitializeComponent();
}
[Obsolete("This constructor only exists for the benefit of the designer...")]
public TAAddInterval() : this(null)
{
}
If you have some sort of fake TAManager you could provide instead, that might avoid NullReferenceException being thrown if the designer happens to hit some code which uses the manager.
You likely just need a parameterless constructor and the designer will work fine.
I'm getting a warning message in Visual Studio 2010 (the one in the title)
Basically I've made a generic form which has a bunch of variables, virtual functions.
It takes a class I made as a parameter and assigns it to a local variable (which is then put as a propety using getters and setters)
I then made another form which inherits from this form. All is well, it runs, but when I attempt to look at the designer of it, I get that error message.
public TAGeneric(TAManager iManager)
{
ControlHelper.SuspendDrawing(this);
mManager = iManager;
SetStyle(ControlStyles.OptimizedDoubleBuffer |
ControlStyles.UserPaint |
ControlStyles.AllPaintingInWmPaint, true);
InitializeComponent();
SetupCommandBar();
ControlHelper.ResumeDrawing(this);
}
Thats the parent.
public TAAddInterval(TAManager iManager) : base(iManager)
{
InitializeComponent();
}
This is a child. Forget the fact I'm using a "manager" when it is frowned upon. Anyone shed some light on the problem? Literally works fine to run, but when it comes to trying to edit the graphical side in designer, It won't load it.
Thanks for the help.
I suspect you need to provide a parameterless constructor for the designer to use:
public TAAddInterval(TAManager iManager) : base(iManager)
{
InitializeComponent();
}
[Obsolete("This constructor only exists for the benefit of the designer...")]
public TAAddInterval() : this(null)
{
}
If you have some sort of fake TAManager you could provide instead, that might avoid NullReferenceException being thrown if the designer happens to hit some code which uses the manager.
You likely just need a parameterless constructor and the designer will work fine.
I've created a custom control, based on the Picturebox:
public class Timebar : System.Windows.Forms.PictureBox
This works correctly if I create the control manually/set all values etc. etc, at the Form's initialization method.
Now I also found this, at the top of the Toolbox: http://i.imgur.com/4KUc0.png
When I try to insert it via msvc, I get an error however.
Failed to create component 'Timebar'. The error message follows:
'System.MissingMethodException: Constructor on type 'SC.Timebar' not found.
This isn't exactly a huge problem with my component Timebar (as I will add that component manually), but it is with the custom Button class I want to make (something more fancy then the default).
There IS a constructor in the class:
public Timebar(Data refr)
{
this._refr = refr;
}
How can I fix the above error?
Thanks,
~ Tgys
Controls used in the designer must have a parameterless constructor. The designer needs to create one of your controls to display and allow you to manipulate it, but it has no clue as to how it should call a constructor that requires parameters.
So, what I would do is create a parameterless constructor which chains the other constructor using a default value, i.e.,
class Foo
{
public Foo() : this(SomeType.Value) { }
public Foo(SomeType whatever) : { /* do stuff /* }
}
I have this classes on the same namespace:
public partial class BaseForm : Form
{
bool isNew = false;
public BaseForm() {}
public BaseForm(bool isNew)
{
InitializeComponent();
this.isNew = isNew;
}
.
.
.
}
public partial class BitSetForm : BaseForm
{
public BitSetForm(bool isNew) : base(isNew)
{
InitializeComponent();
}
new private void InitializeComponent()
{
.
.
.
}
}
1) And I got this warning: Could not find type "..BaseForm," Please make sure that the assembly that contains this type is referenced. If this type is a part of your development project, make sure that the project has been successfully built using the setting for your current platform or Any CPU.
2) Design-Time Errors in the Windows Forms Designer appears and hiding the design pane of the "BitSetForm" win-form.
What does this mean? What can I do to make the design pane of the "BitSetForm" win-form display again?
You need to add a parameterless constructor to your BaseForm.
It can even be private; it just needs to exist.
Without one, the designer is unable to create an instance of the BaseForm to show in the design surface.
Remember to call InitializeComponent in the constructor.
Well a couple things...
You need to build your application before the designer can instantiate your base class. This can be very difficult if your subclass form has a bunch of errors.
The designer can only instantiate a class that has a default parameterless constructor. So that means your base class's BaseForm(bool isNew) will never be called by the designer. Which means InitializeComponent will not either. You should move InitializeComponent to the parameterless constructor and have the second constructor call the first.
InitializeComponent is private by default. You should not change its visibility to protected and since it's private, no new modifier is needed.
InitializeComponent should never be chained that way to the base class. It should only be called by the constructor.
Given all those issues, I would highly recommend either giving up on Windows Forms inheritance or at least moving your base class into a separate assembly. I've tried it many times and it's more trouble than it's worth.
The key thing to remember is that when you're viewing a form in the designer, the designer is not creating an instance of the form you see - it's creating an instance of the base class. At runtime that is obviously not the case. So it's very common to see different runtime/design time behavior.
As mentioned by #SLaks, you need the InitializeComponent in the constructor of your class. I would actually have it in the no-parameter instance. Then, in the constructor of you boolean, i would change to
public partial class BaseForm : Form
{
bool isNew = false;
public BaseForm()
{
InitializeComponent();
}
public BaseForm(bool isNew) : this()
{
this.isNew = isNew;
}
}
So if you had other stuff you wanted performed within your BaseForm definition regardless of a parameerized startup, that too would be called. This way, the InitializeComponent is triggeed in EITHER case.