Re: Get Variable Type from String - C# Discussion Boards

Re: Get Variable Type from String

SledgeHammer017-Aug-12 18:55

SledgeHammer01

7-Aug-12 18:55

PIEBALDconsult wrote:
I recommend an enumeration:

I wouldn't. You are re-inventing the wheel by re-inventing something that already exists in .Net. .Net has full support for creating instances from types and/or type strings. I provided sample code in my other response. No need to "fake it" with enums.

Re: Get Variable Type from String

SledgeHammer017-Aug-12 18:52

SledgeHammer01

7-Aug-12 18:52

You can re-write all of that code in one or two lines. You didn't mention who is calling the Goto function, but you can convert a string into a Type like this:

Type type = Type.GetType(viewModel);

Then you'd get the workspace:

var workspace = _mainWindow.Workspaces.FirstOrDefault(vm => vm is type);

Then you'd create the VM from the type like this:

Activator.CreateInstance(type, new object[] { claimId });

Re: Get Variable Type from String

PIEBALDconsult8-Aug-12 3:46

PIEBALDconsult

8-Aug-12 3:46

So how do you restrict the allowable types?

Re: Get Variable Type from String

Shameel8-Aug-12 4:49

Shameel

8-Aug-12 4:49

Store the list of allowable types in a string array and check the array before the call to GetType, perhaps?

Re: Get Variable Type from String

SledgeHammer018-Aug-12 7:39

SledgeHammer01

8-Aug-12 7:39

Check if the type is derived from the ViewModelBase or implements an interface, but that wasn't a requirement Smile | :)

Re: Get Variable Type from String

eddieangel8-Aug-12 6:01

eddieangel

8-Aug-12 6:01

This is what I was looking for. I had stumbled across the Activator but was not sure how to use it in this example. I have no need to restrict the allowable types in this instance, so this is perfect.

Cheers, --EA

Re: Get Variable Type from String

eddieangel8-Aug-12 6:23

eddieangel

8-Aug-12 6:23

Solution did not work exactly as I thought it might. This is where I am at right now:

GoTo call:

public ICommand GoToECRsCommand { get { return new RelayCommand(() => GoTo<ECRsViewModel>("ECRsViewModel", _claimId)); } }

Eventually it will be either the <t> or the viewModel argument, not both. Here is the function right now:

private void GoTo<T>(int claimId) where T : new()
{
    var workspace = _mainWindow.Workspaces.FirstOrDefault(vm => vm is T)
        as T;

    if (workspace == null)
    {
        workspace = new T(claimId);
        _mainWindow.Workspaces.Add(workspace); //error Unknown method add(T)
    }
    _mainWindow.SetActiveWorkspace(workspace);
}

Obviously the issue stems from my lack of understanding of generic types (Amongst other things). I can see the problem, I just don't know how to correct it.

Cheers, --EA

Re: Get Variable Type from String

SledgeHammer018-Aug-12 7:44

SledgeHammer01

8-Aug-12 7:44

What is the real error that the debugger is putting out?

"var workspace" should be "T workspace" if you are going that route and you might be able to drop the "as T" part.

When you new up the workspace like that, is it actually returning the correct type and calling the proper constructor? I'm surprised that the compiler didn't error out on that line because it doesn't know that some random T has a constructor(int), although it may do that at compile time...

Re: Get Variable Type from String

eddieangel8-Aug-12 8:54

eddieangel

8-Aug-12 8:54

Having gutted out much of what was there, here is where I am:

private void GoTo(string viewModel, int claimId)
{
    Type type = Type.GetType(viewModel);
    var workspace = _mainWindow.Workspaces.FirstOrDefault(vm => vm is type); //Error on type

    if (workspace == null)
    {
        Activator.CreateInstance(type, new object[] { claimId });
        _mainWindow.Workspaces.Add(workspace);
    }
    _mainWindow.SetActiveWorkspace(workspace);
}

Error is "The type or namespace 'type' could not be found."

Re: Get Variable Type from String

Pete O'Hanlon8-Aug-12 9:27

Pete O'Hanlon

8-Aug-12 9:27

Change that line to:

var workspace = _mainWindow.Workspaces.FirstOrDefault(vm => vm.GetType().Equals(type));

*pre-emptive celebratory nipple tassle jiggle* - Sean Ewington

"Mind bleach! Send me mind bleach!" - Nagy Vilmos

CodeStash - Online Snippet Management | My blog | MoXAML PowerToys | Mole 2010 - debugging made easier

Re: Get Variable Type from String

SledgeHammer018-Aug-12 9:32

SledgeHammer01

8-Aug-12 9:32

Oh... DUH... you can't do the "is type" part because is expects an actual type, not a Type. How's that for confusing Smile | :)

. I.e. you do blah is Window, not blah is window.GetType().

So you can either change it to:

vm.GetType() == type

Or go back to your generic method you had before and do:

vm is T

but with the above code, you need to do the vm.GetType() == type.

Re: Get Variable Type from String

SledgeHammer018-Aug-12 9:33

SledgeHammer01

8-Aug-12 9:33

btw, you are missing a:

workspace = Activator.CreateInstance(type, new object[] { claimId });

Re: Get Variable Type from String

eddieangel8-Aug-12 13:24

eddieangel

8-Aug-12 13:24

Unfortunately making that changes causes an error.

An instance of type 'object' can not be assigned to a variable of type WorkspaeViewModel.

Re: Get Variable Type from String

SledgeHammer018-Aug-12 13:44

SledgeHammer01

8-Aug-12 13:44

Ok, so you need the T casts Smile | :)

workspace = (T)Activator.CreateInstance(type, new object[] { claimId });

Re: Get Variable Type from String

eddieangel9-Aug-12 6:46

eddieangel

9-Aug-12 6:46

I needed that and also:

private void GoTo<T>(string viewModel, int claimId) where T: WorkspaceViewModel

However, this line:

Type type = Type.GetType(viewModel);

That returns null so everything else falls apart. How does it get a type from a string name? And can I pull out the string? It seems redundant since I am already giving it the type.

I can use T here:

var workspace = _mainWindow.Workspaces.FirstOrDefault(vm => vm is T);

and that gets rid of the need for type up until here:

workspace = (T)Activator.CreateInstance(type, new object[] { claimId });

Ayudame.

Cheers, --EA

Incidentally, without the "where T: WorkspaceViewModel I get an error on the workspace = (T)Activator... line.

Re: Get Variable Type from String

eddieangel9-Aug-12 6:55

eddieangel

9-Aug-12 6:55

Blargh.

For no apparent reason I had to use the fully qualified name.

So, the call looks like this:

GoTo<ClaimReportsViewModel>("litMan.ClaimReportsViewModel", _claimId)

Not sure why I have to do it that way, but it works. C'est la vie.

Re: Get Variable Type from String

SledgeHammer019-Aug-12 7:58

SledgeHammer01

9-Aug-12 7:58

Lol, you keep switching between the two methods haha... now you are combining both of them... you should do:

GoTo<ClaimReportsViewModel>(_claimId)

Now you don't need the Type.GetType() line anymore. Your var workspace... line is correct. To fix the Activator.CreateInstance line, do:

workspace = (T)Activator.CreateInstance(typeof(T), new object[] { claimId });

Now you are using the generic method throughout Smile | :)

Re: Get Variable Type from String

eddieangel9-Aug-12 8:02

eddieangel

9-Aug-12 8:02

I had a strong desire to get away from the mix and match, but I did not have the typeof(T) piece, I assumed you could just put the T in there and it did not work.

I tried Type.GetType(T) and T.GetType() to no avail. There are too many methods to find a type.

Regardless, thank you for the extensive help.

This is the final reslt:

public ICommand GoToECRsCommand { get { return new RelayCommand(() => GoTo<ECRsViewModel>(_claimId)); } }

private void GoTo<T>(int claimId) where T: WorkspaceViewModel
		{	
			var workspace = _mainWindow.Workspaces.FirstOrDefault(vm => vm is T);

			if (workspace == null)
			{
				workspace = (T)Activator.CreateInstance(typeof(T), new object[] { claimId });
				_mainWindow.Workspaces.Add(workspace);
			}
			_mainWindow.SetActiveWorkspace(workspace);
		}

Cheers, --EA

Re: Get Variable Type from String

Pete O'Hanlon7-Aug-12 22:27

Pete O'Hanlon

7-Aug-12 22:27

In my Goldlight[^] project, I have included a WorkspaceManager that might just be of help. Basically, any VM that needs to be treated as though it should be in a workspace inherits from WorkspaceViewModelBase (this provides things like the ability to close the particular workspace).

I then use this information to look the workspace up. Basically, the workspaces are maintained in an ObservableCollection and the UI binds to this.

It's all pretty simple to use. If you have any questions about the code, please feel free to ask.

*pre-emptive celebratory nipple tassle jiggle* - Sean Ewington

"Mind bleach! Send me mind bleach!" - Nagy Vilmos

CodeStash - Online Snippet Management | My blog | MoXAML PowerToys | Mole 2010 - debugging made easier

Re: Get Variable Type from String

eddieangel8-Aug-12 6:02

eddieangel

8-Aug-12 6:02

I am using a Workspace viewModel right now that works as you have described. I can't recall where I got it, I think was an MSDN article from a year or two ago. Still, I will check out your framework is the workspace setup is a bit clunky, requiring a lot of defining throughout the project. Something more concise would be great.

Thanks for the heads up, I am always trying to find pieces like this.

Cheers, --EA

Re: Get Variable Type from String

eddieangel8-Aug-12 6:42

eddieangel

8-Aug-12 6:42

I just have to come back and say this framework is great. It is very feature rich. I am so deeply invested in the architecture right now (including MVVMLight) that I am apprehensive about switching over. There are a lot of tempting pieces though. This is definitely going to require some additional looking into.

Re: Get Variable Type from String

Pete O'Hanlon8-Aug-12 7:31

Pete O'Hanlon

8-Aug-12 7:31

Thanks. I wouldn't recommend switching over, Laurent did a really great job with MVVM Light - I mainly pulled it together to make it easy to combine MVVM with some of the things that you would typically use PRISM to do (as well as providing inbuilt support for theming). Please feel free to cannibalise it to your hearts content.

*pre-emptive celebratory nipple tassle jiggle* - Sean Ewington

"Mind bleach! Send me mind bleach!" - Nagy Vilmos

CodeStash - Online Snippet Management | My blog | MoXAML PowerToys | Mole 2010 - debugging made easier

FarsiLibrary

amin_alexi7-Aug-12 2:02

amin_alexi

7-Aug-12 2:02

hi I used the farsilibrary of code project but have error on my project,that namespace of Win does nor exist!
I add the dll of farsiLibrary and add FArsiLibrary.Win in my tools and drag the persiandatepicker on my form but when i want run my project it gets this error!I paste dll of all in my bin folder but nothin happen!
how can i solve it?

Re: FarsiLibrary

Dave Kreskowiak7-Aug-12 2:11

Dave Kreskowiak

7-Aug-12 2:11

Ask this question in the forum at the bottom the article you got the library from.

You might also want to paste in the text of the error message you got. Just saying "it doesn't work" doesn't give enough information for anyone to help you.

A guide to posting questions on CodeProject[^]

Dave Kreskowiak

Video Recording from a DVR using EMGU or DirectShow C#

Gertlaub26-Aug-12 23:26

Gertlaub2

6-Aug-12 23:26

SQL

Hi. I'm in need of recording video from a 4 channel DVR from .net C#. I've looked at EMGU a Opencv .net wrapper as well as the DirectShow .net library to do this. I've decided to give EMGU a go and is quite happy with it when using webcams. Now I want to use a 4 channel H.264 Usb DVR for the same purpose, but I don't know how to select a video channel on the DVR. When running the sample capture application of EMGU I only get a black screen. I have the same problem with DirectShow. It picks up the DVR as a DR 3101_3104 Video Capture device, but is also showing me the black screen.
Note that the camera is working fine, when I use "SuperDVR"(software that came included with the DVR).

I think there must be a way to specify the channel of which camera you want in both of these libraries, but I have no idea. Could someone shed some light on my problem please.

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