My problem is, that I can't use my getter in my other class because the getter is in the MainWindow.xaml.cs class.
When I use this Code* in my other class ControlKey.cs I get an exception that the Application is hold on. I think it want's to create an other Window but I just want to use the getter in the class ControlKey.cs
MainWindow.xaml.cs Class:
public bool GetPresentationStarted(){
return presentationsarted;
}
*
ControlKey.cs Class:
MainWindow mWindow = new MainWindow();
bool presentationStarted;
And later I have an if statement where I do something if presentationStarted is true.
...
presentationStarted = mWindow.GetPresentationStarted();
...
if (presentationStarted == true) {
...
}
I don't know how to do it different. I hope someone can help me
Each instance of MainWindow has its own copy of presentationsarted. If you want the value of presentationsarted from the main window of your application, you can't just create a new instance of MainWindow. That new instance has nothing to do with the other instance that's already showing.
But you can get the actual main window itself.
var mWindow = (MainWindow)App.Current.MainWindow;
var x = mWindow.GetPresentationStarted();
That'll work, but it's not the best way to write a WPF application. You should really learn the MVVM ("Model-View-ViewModel") pattern. Then each window would have its own viewmodel that owns properties like that one, and all the viewmodels can share a reference to some common viewmodel that has state everybody cares about. WPF with the MVVM pattern is immensely powerful. The learning curve is rough, however.
Because you don't require any other parameters from the MainWindow class just try to use:
1. Static property. For example, you can create
public static bool? MainWindow.PresentationStarted {get; private set;}
and set the value from any event you prefer.
Or
2.Create shared instance like:
public static bool? SharedClass.MainPresentationStarted {get; set;}.
So you have an access to the value:
if (MainWindow.PresentationStarted == true)
Related
What I want to do:
I want do change a background color of a button from anywhere in my code (other classes Xamarin Forms). For example a button A in Page A changes the color of button B in Page B
on Windows you can use the MethodInvoker Delegat which isn't available on Android/iOS.
Can you give me a hint?
I tried it with the text of the buttons before with the MVVM approach.
in my PageB.xaml:
<Button Name="Button_B" Text="{Binding MyText}"/>
in my PageB.cs in public PageB
BindingContext = new MVVMPageB();
in my MVVMPageB.cs
private string myText;
public string MyText
{
get => mytring;
set
{
mystring = value;
PropertyChanged?
.Invoke(this, new PropertyChangedEventArgs(MyText)));
}
if i call:
MyText("Test");
in my MVVMPageB.cs it works fine. but i dont know how to access this from anywhere else.
i tried:
var Testobjekt = new MVVMPageB() //pretty sure thats not correct
Testobjekt.MyText("Test"); //wont work
Technique 1
This is a Singleton pattern for MVVMPageB.
This works if you never have two "Page B"s. IF there is a Page B on the navigation stack (so you can "Go Back" to it), and you display ANOTHER Page B, THEN this will not work well, because both Page B's will refer to the SAME MVVMPageB instance.
public class MVVMPageB : ...
{
// "Singleton": This is the only instance of MVVMPageB.
private static MVVMPageB _It;
public static MVVMPageB It
{
if (_It == null)
_It = new MVVMPageB();
return _It;
}
// Your constructor.
// It is private; only used via "It" getter above.
private MVVMPageB()
{
...
}
}
Code in another class, to access a member of the MVVMPageB.
MVVMPageB.It.MyText("Test");
Replace this code:
BindingContext = new MVVMPageB();
With this code:
BindingContext = MVVMPageB.It;
NOTE: Because MVVMPageB.It is static, if you go to Page B a second time, it will show the values you had last time (within the same app session).
Technique 2
A more robust approach, which works even if you create another Page B, requires having some way to pass the current instance of MVVMPageB to MVVMPageA or to PageA.
A complete example depends on exactly how/where you create each page. But this shows the idea.
public class MVVMPageB : ...
{
// Your constructor. Add parameters as needed.
public MVVMPageB()
{
...
}
}
public partial class PageB : ...
{
// Convenience property - our BindingContext is type MVVMPageB.
public MVVMPageB VMb => (MVVMPageB)BindingContext;
...
}
public class MVVMPageA : ...
{
// This is here, so both MVVMPageA and PageA can find it.
public MVVMPageB VMb;
}
public partial class PageA : ...
{
// Convenience property - our BindingContext is type MVVMPageA.
public MVVMPageA VMa => (MVVMPageA)BindingContext;
...
}
Code that creates Page B and then Page A:
var pageB = new PageB();
var pageA = new PageA();
// Tell MVVMPageA about MVVMPageB.
pageA.VMa.VMb = pageB.VMb;
Methods in MVVMPageA can now access members of MVVMPageB:
VMb.MyText("Test");
Methods in PageA can now access members of MVVMPageB:
VMa.VMb.MyText("Test");
NOTE: In this dynamic technique, if you go to Page B a second time (in the same app session), it will have a new instance of MVVMPageB.
You need a singleton viewModel for this use. I usually use one for the navbar.
So every scoped page viewModel references the singleton global viewModel inside:
PageAViewModel has property NavBarModel
PageBViewModel has property NavBarModel
and so on..
So it's obvious your button will be bind as
BackgroundColor={Binding NavBarModel.ActionColor} on every different page.
Now to have a singleton and obtain its reference i can see two ways: dependency injection (DI) or single instance creation. You can read a lot about DI on the net, while for a simple case you can have a single instance model with a prop like:
private NavBarModel _current;
public NavBarModel Current
{
get
{
if (_current == null)
_current = new NavBarModel();
return _current;
}
}
then in pages viewModels constructor set NavBarModel = NavBarModel.Current;
You would need DI though to reference more models inside your singleton, or/and make your code more reusable. Good luck.
I have the following Singleton Pattern for the ViewModel of my Options:
private static volatile GeneralOptionsViewModel instance;
private static object syncRoot = new object();
/// <summary>
/// threadsave singleton
/// </summary>
public static GeneralOptionsViewModel Instance
{
get
{
if (instance == null)
{
lock (syncRoot)
{
if (instance == null)
instance = new GeneralOptionsViewModel();
}
}
return instance;
}
}
In my XAML I have a color picker from the extended toolkit package:
<xctk:PropertyGridEditorColorPicker Background="Transparent" Name="face"
Margin="5,0" Width="50" BorderBrush="#32FFFFFF" BorderThickness="1"
SelectedColor="{Binding FaceRectColor, Mode=OneWayToSource,
UpdateSourceTrigger=PropertyChanged}"/>
As you can see it is bound to FaceRectColor property of the GeneralOptionsViewModel class which is defined like follows.
Within the setter there is a conversion to MCvScalar (also a property of the same class), the format I later need for my application:
public Color FaceRectColor
{
get
{
return faceRectColor;
}
set
{
if (faceRectColor != value)
{
faceRectColor = value;
FaceRectColorScalar = new MCvScalar(value.B, value.R, value.G, value.A);
SetProperty(ref faceRectColor, value);
}
}
}
My problem now is, that the binding works and also the correct values are written to the variable, however when I call the singleton with the property from a different class - and from a different thread - it always shows zero for all color channels. However, if I break the program directly within the singleton class I can see the correct values. AFAIK the singleton should be threadsafe, so I'm looking for the reason of this behavior.
My guess is some threading issue, since other properties from the singleton class are displayed correctly, but they are only called in the main thread.
Edit: In my case all property values of the singleton class are set before the worker thread is active. This means no changes during the time the worker thread is active.
Edit II: Here is the complete project for code evaluation.
In the class CameraViewModel in line 202 is the relevant call for a function, where I want to pass the values from the singleton.
Your "singleton" contains a public constructor which effectively makes it a non-singleton. And you are not binding to the singleton in your GeneralOptionsView.
If you really want GeneralOptionsViewModel to be a singleton, you should implement it like this:
public sealed class GeneralOptionsViewModel : ViewModelBase
{
private static readonly GeneralOptionsViewModel _instance = new GeneralOptionsViewModel();
private GeneralOptionsViewModel()
{
GetAvailableCameraList();
DetectorTypeList = new List<string>() { "Cascade Detector" };
SelectedDetectorTypeIndex = 0;
}
public static GeneralOptionsViewModel Instance => _instance;
//...
}
You should then set the DataContext of your view to the singleton:
<Grid DataContext="{Binding Source={x:Static local:GeneralOptionsViewModel.Instance}}">
When your property changes and it does so on a different thread, the calls that are made to notify everybody (in particular the UI) of this change are running in the calling thread. Accessing the UI in a thread that is not the UI thread is a bad idea. It might sometimes work. But it will fail sooner or later.
The solution to your current problem is changing the property in the UI thread.
That said, maybe you should think about whether you need a Singleton. That's a huge red flag that something is wrong with the structure of your program. You don't need a Singleton. Nothing bad would happen if some other context had a second settings viewmodel. You seem to want a Singleton because it's so nice and easy to have a global variable. That is the drawback of a Singleton. It's disadvantage that you buy into because you need something from this pattern. If you find you are using this pattern only because it's disadvantage gives you an excuse to have a global variable, you are doing patterns wrong. It's an anti-pattern.
I have a main form and I need in other class get or set field from Main Form. I created public property in Main Form:
public partial class MainForm : Form
{
public string get_txt()
{
return phone.Text; //phone - textbox
}
}
But in other class I can't get this property:
MessageBox.Show(MainForm.get_txt); //there error. It doesn't seemed get_txt property.
I'm sorry for this simpliest question, but I really don't know this. Everywhere wrote that simpliest way to do it - in class of Main Form create public property for needed private field in Main Form. What do I wrong?
So the MessageBox.Show(MainForm.get_txt) won't compile as you're trying to refer to a static property, not an instance method.
I'm not a winforms dev, so this is a bit of a guess:
Somewhere in your code you will have a call like var main = new MainForm(). On that instance i.e. main you will be able to call main.get_txt().
As a side note, given that you're working in C# it'd be good to name the method to something a little more idiomatic, perhaps public string GetPhoneNumber() or better yet make it a property:
public string PhoneNumber
{
get { return phone.Text; }
}
Make instance of MainForm and than call it.
Mainform _mainform=new Mainform();
MessageBox.Show(_mainform.Get_text);
Your MainForm is not static class, you can not use like that. If u want access the MainForm(methods or variables), you have to assing the variable.
MainForm mForm = new MainForm();
MessageBox.Show(mForm.getText());
Thanks to you all.
but when I create a new istance of Main Form all controls in it will be initializing like in my current Main Form?
I'm trying to work with Windows Forms and User Controls and thus far it's been nothing but a headache. I can't make the form or the controls static because the designer doesn't like that and when I use Singleton on my form and controls, the designer still throws errors at me.
My FormMain:
public partial class FormMain : Form
{
private static FormMain inst;
public static FormMain Instance
{
get
{
if (inst == null || inst.IsDisposed)
inst = new FormMain();
return inst;
}
}
private FormMain()
{
inst = this;
InitializeComponent();
}
MainScreen.cs:
public partial class MainScreen : UserControl
{
private static MainScreen inst;
public static MainScreen Instance
{
get
{
if (inst == null || inst.IsDisposed)
inst = new MainScreen();
return inst;
}
}
private MainScreen()
{
inst = this;
InitializeComponent();
}
If the constructor of MainScreen is public the program runs, but when I change it to private I now get an error in FormMain.Designer.cs saying "'Adventurers_of_Wintercrest.UserControls.MainScreen.MainScreen()' is inaccessible due to its protection level". It points to this line:
this.controlMainScreen = new Adventurers_of_Wintercrest.UserControls.MainScreen();
I think this is the instance of the class that the designer makes by default. Should I ditch the designer? Or is there a way around this? Or is there another way to make class properties accessible without using Singleton (since I can't seem to make the form or controls static)? Any help would be greatly appreciated.
You need to keep a reference to each instance of each form if you want to access the public properties of the instantiated form.
One way is to have a class with a static variable for each type of form:
class FormReferenceHolder
{
public static Form1 form1;
public static Form2 form2;
}
This way you would set the static variable whenever you instantiate a form, and then you can access that variable from anywhere in the program. You can go one step further with this and use properties that set up the form if it doesn't already exist:
class FormReferenceHolder
{
private static Form1 form1;
public static Form1 Form1
{
get
{
if (form1 == null) form1 = new Form1();
return form1 ;
}
}
}
...
static void Main()
{
Application.Run(FormReferenceHolder.Form1 );
}
I think I answered a previous question about this, which looks like it is what got you started down this route. The first point is that I wasn't recommending this pattern specifically, just trying to teach you more about how software developers can manage scope.
That said, the problem you are facing isn't insurmountable. You could hobble a public constructor by throwing an exception at runtime and not at design time, for instance, and modify Program.cs to use the static Instance instead of manually constructing the form.
But.
As I said in the other question, the better option would be to change architecture so that you don't need your library code to directly manipulate the GUI in the first place.
You can do this either by just having the GUI ask the library questions when it thinks it needs new data (simple functions) or by letting the GUI be notified when something needs to change. Either method would be better than having the library fiddle with labels directly.
A good place to start would be something like an MVC (model-view-controller) architecture, which I was alluding to in my previous answer. It might be best, though, to give us an idea of what your high-level program structure looks like now on a bit more detail. What are the main classes you are using in your system (not just the ones you've mentioned so far)? What is the main responsibility of each, and where does each live? Then our recommendations could be a little more specific.
EDIT
So, I have mocked up a quick demo of a possible alternative architecture, based on your comment.
I have the following in my project:
FormMain (Form)
TitleScreen (UserControl)
InGameMenu (UserControl)
MainScreen (UserControl)
GameController (Class)
GameModel (Class)
I didn't use Date and LoadSave, for now.
FormMain simply has an instance of each UserControl dropped on it. No special code.
GameController is a singleton (since you tried to use this pattern already and I think it would be helpful for you to try using a working version of it) that responds to user input by manipulating the model. Note well: you don't manipulate the model directly from your GUI (which is the View part of model-view-controller). It exposes an instance of GameModel and has a bunch of methods that let you perform game actions like loading/saving, ending a turn, etc.
GameModel is where all your game state is stored. In this case, that's just a Date and a turn counter (as if this were going to be a turn-based game). The date is a string (in my game world, dates are presented in the format "Eschaton 23, 3834.4"), and each turn is a day.
TitleScreen and InGameMenu each just have one button, for clarity. In theory (not implementation), TitleScreen lets you start a new game and InGameMenu lets you load an existing one.
So with the introductions out of the way, here's the code.
GameModel:
public class GameModel
{
string displayDate = "Eschaton 23, 3834.4 (default value for illustration, never actually used)";
public GameModel()
{
// Initialize to 0 and then increment immediately. This is a hack to start on turn 1 and to have the game
// date be initialized to day 1.
incrementableDayNumber = 0;
IncrementDate();
}
public void PretendToLoadAGame(string gameDate)
{
DisplayDate = gameDate;
incrementableDayNumber = 1;
}
public string DisplayDate
{
get { return displayDate; }
set
{
// set the internal value
displayDate = value;
// notify the View of the change in Date
if (DateChanged != null)
DateChanged(this, EventArgs.Empty);
}
}
public event EventHandler DateChanged;
// use similar techniques to handle other properties, like
int incrementableDayNumber;
public void IncrementDate()
{
incrementableDayNumber++;
DisplayDate = "Eschaton " + incrementableDayNumber + ", 9994.9 (from turn end)";
}
}
Things to note: your model has an event (in this case, just one of type EventHandler; you could create more expressive types of events later, but let's start simple) called DateChanged. This will be fired whenever DisplayDate changes. You can see how that happens when you look at the property definition: the set accessor (which you will NOT call from your GUI) raises the event if anyone is listening. There are also internal fields to store game state and methods which GameController (not your GUI) will call as required.
GameController looks like this:
public class GameController
{
private static GameController instance;
public static GameController Instance
{
get
{
if (instance == null)
instance = new GameController();
return instance;
}
}
private GameController()
{
Model = new GameModel();
}
public void LoadSavedGame(string file)
{
// set all the state as saved from file. Since this could involve initialization
// code that could be shared with LoadNewGame, for instance, you could move this logic
// to a method on the model. Lots of options, as usual in software development.
Model.PretendToLoadAGame("Eschaton 93, 9776.9 (Debug: LoadSavedGame)");
}
public void LoadNewGame()
{
Model.PretendToLoadAGame("Eschaton 12, 9772.3 (Debug: LoadNewGame)");
}
public void SaveGame()
{
// to do
}
// Increment the date
public void EndTurn()
{
Model.IncrementDate();
}
public GameModel Model
{
get;
private set;
}
}
At the top you see the singleton implementation. Then comes the constructor, which makes sure there's always a model around, and methods to load and save games. (In this case I don't change the instance of GameModel even when a new game is loaded. The reason is that GameModel has events and I don't want listeners to have to unwire and rewire them in this simple sample code. You can decide how you want to approach this on your own.) Notice that these methods basically implement all the high-level actions your GUI might need to perform on the game state: load or save a game, end a turn, etc.
Now the rest is easy.
TitleScreen:
public partial class TitleScreen : UserControl
{
public TitleScreen()
{
InitializeComponent();
}
private void btnLoadNew(object sender, EventArgs e)
{
GameController.Instance.LoadNewGame();
}
}
InGameMenu:
public partial class InGameMenu : UserControl
{
public InGameMenu()
{
InitializeComponent();
}
private void btnLoadSaved_Click(object sender, EventArgs e)
{
GameController.Instance.LoadSavedGame("test");
}
}
Notice how these two do nothing but call methods on the Controller. Easy.
public partial class MainScreen : UserControl
{
public MainScreen()
{
InitializeComponent();
GameController.Instance.Model.DateChanged += Model_DateChanged;
lblDate.Text = GameController.Instance.Model.DisplayDate;
}
void Model_DateChanged(object sender, EventArgs e)
{
lblDate.Text = GameController.Instance.Model.DisplayDate;
}
void Instance_CurrentGameChanged(object sender, EventArgs e)
{
throw new NotImplementedException();
}
private void btnEndTurn_Click(object sender, EventArgs e)
{
GameController.Instance.EndTurn();
}
}
This is a little more involved, but not very. The key is, it wires up the DateChanged event on the model. This way it can be notified when the date is incremented. I also implemented another game function (end turn) in a button here.
If you duplicate this and run it, you'll find that the game date is manipulated from lots of places, and the label is always updated properly. Best of all, your controller and model don't actually know anything at all about the View-- not even that it's based on WinForms. You could as easily use those two classes in a Windows Phone or Mono context as anything else.
Does this clarify some of the architecture principles I and others have been trying to explain?
In essence the problem is that when the application runs, it's going to try to instantiate the main form-window. But by using the Singleton pattern, you're essentially forbidding the application from doing that.
Take a look at the sample code here:
http://msdn.microsoft.com/en-us/library/system.windows.forms.application.aspx
You'll notice in particular this section:
[STAThread]
public static void Main()
{
// Start the application.
Application.Run(new Form1());
}
Notice how the program is trying to instantiate Form1. Your code says, nah, I don't really want that since you mark the constructor as private (same holds true for static forms as well). But that's counter to how windows forms is supposed to work. If you want a singleton form-window, just don't make any more. Simple as that.
I have a method that executes inside one form, but I need to retrieve data from another form to pass into the method.
Whats the best way of doing this?
You can expose a property on one form and call it from the other. Of course you'll need some way of getting the instance of form1. You could keep it as a static property in the program class or some other parent class. Usually in this case I have a static application class that holds the instance.
public static class Application
{
public static MyForm MyFormInstance { get; set; }
}
Then when you launch the first form, set the application MyFormInstance property to the instance of the first Form.
MyForm instance = new MyForm();
Application.MyFormInstance = instance;
Add a property to the second form.
public String MyText
{ get { return textbox1.Text; }
set { textbox1.Text = value; }
}
And then you can access it from your second form with:
Application.MyFormInstance.MyText
On the form that has the textbox you need data from, expose either a Property or a Method that returns the text. IE:
internal string TextBoxTest
{
get{ return this.textBox1.Text;}
}
There is a similar post here
The videos below will clear up a lot of your concepts about passing data between 2 forms.
There are multiple ways to pass data between 2 forms check these links which has example videos to do this
FormToForm Using Properties - http://windowsclient.net/learn/video.aspx?v=108089
FormToForm Using Parameters - http://windowsclient.net/learn/video.aspx?v=105861
HTH
Assuming that formB is initialized in formA I would recommend adding a string to the constructor of formB sending the Texbox1.Text
as in
class formB: Form{
private string data;
public formB(string data)
{
InitializeComponent();
this.data = data;
}
//rest of your code for the class
}
Don't do this.
Longer version: Why is your view directly interacting with another view?
Much longer version:
Rather than making a public property that exposes the field, it would provide better encapsulation and insulation from change if the form with the field of interest interacted with some form of data object, which was then passed to the interested method.
The location of the interested method should be carefully considered - if it controls aspects of the view (WinForm, in your case), then it may be appropriately a member of that class - if not, perhaps its real home is in the data object?