Re: DependancyProperty Confusion with Custom Controls and ModelView - WPF Discussion Boards

Re: DependancyProperty Confusion with Custom Controls and ModelView

2-Dec-10 11:58

Well, its a retarded way to do it and he should unretard it. Not make it more retarded Smile | :)

. If he did it the correct way, he wouldn't be trouble shooting wacky issues. Oh wellz Smile | :)

PaulPrice3-Dec-10 0:11

Re: DependancyProperty Confusion with Custom Controls and ModelView

3-Dec-10 0:11

Concerning the Retaded way this is done, can you elaborate? I am not sure I understand what you think is wrong with my MVVM implementation.

I am not shooting or getting upset, please do not misread my comment in that way, I am only trying to learn.

All of the source code is available above. How would you achieve MVVM?

Just racking up the postings

PaulPrice3-Dec-10 0:05

Re: DependancyProperty Confusion with Custom Controls and ModelView

3-Dec-10 0:05

Ian,

You are correct in the way DataContext is set. I am using a method learned from one of the MVVM mechanism described on a tutorial published in CodeProject, I forget the Authors name right now, search WPF MVVM.

As mentioned in another comment, I do somehow have this working and will publish my fixes here when I have got close to understanding how I fixed it. Something to do wth the MetaData part and creating an instance of the list in the constructor. Like I said, I will put my changes up as soon as I can.

I also appreciate that I may have a single list instance issue as mentioned by SledgeHammer.

Again, thanks for your time, there is nothing worse than head butting a brick wall.

Just racking up the postings

SledgeHammer012-Dec-10 6:35

Re: DependancyProperty Confusion with Custom Controls and ModelView

2-Dec-10 6:35

1) First issue I see is that your dependency properties are set up incorrectly.

Think about whats happening here... SelectedItemsProperty and DeSelectedItemsProperty are static (meaning a single instance in this case). You have set the values to new ObservableCollection<object>(). What you end up with is *EVERY* DualListControl in the world is using the same ObservableCollection<object>(). You also allow users to overwrite the collections completely. Not something you want to do.

Use DependencyProperty.RegisterReadOnly() to register the property as a read-only DP and create the ObservableCollection<object>() in the public DualListControl() constructor. Something like:

public DualListControl()
{
SetValue(SelectedItemsPropertyKey, new ObservableCollection<object>());
}

then remove the setters for those properties.

2) Bindings in generic.xaml should be TemplateBinding, not binding.

PaulPrice2-Dec-10 7:05

Re: DependancyProperty Confusion with Custom Controls and ModelView

2-Dec-10 7:05

SledgeHammer, Thanks for your time and comments

Re point one,

DependancyProperties obviously still confuse the life out of me!
I tried making this a readonly collection and then realised what you are suggesting, you have given me the method required if I want a single list for all DualListControls right? but these can no longer be ovverriden by a user.

That is not my intention, what I am trying to achieve and failing is to be allow a developer to do something like this

<Grid>
    <CustomControls:DualListControl Name="List" SelectedItems="{Binding SelectedItemsA}" DeSelectedItems="{Binding DeslectedItemsA}"/>
</Grid>

The problem I appear to have is that the SelectedItems dependancy property is not being bound to the one in the MainAppViewModel.

Re point two,

Ian has already found this and corrected me, the bindings in the Generic.xaml are now as the follows

<ListView Grid.Column="2" Name="ElementSelectedList" ItemsSource="{TemplateBinding SelectedItems}"/>

Have I understood this correctly?

Just racking up the postings

SledgeHammer012-Dec-10 10:04

Re: DependancyProperty Confusion with Custom Controls and ModelView

2-Dec-10 10:04

No, what you have *NOW* will result in every DualListControl sharing the same ObservableCollection instance. I'll assume that you want each one to have its own. The solution I gave you will give each instance its own collection.

The UserControl doesn't have its DataContext set, so those Binding will not work.

The bindings in Generic.xaml should be TemplateBinding.

PaulPrice2-Dec-10 23:59

Re: DependancyProperty Confusion with Custom Controls and ModelView

2-Dec-10 23:59

SledgeHammer,

I appreciate your time.

I understand your point about a single list instance being shared amongst all controls. Please understand that I have been making changes as recommended by yourself and Ian (above).

The complication that arises with the ReadOnly method you describe is that I would like to be able to allow the consumer to use the control in the following way. The ReadOnly method does not allow me to do this.

Any suggestions?

<CustomControls:DualListControl SelectedItems="{Binding SelectedItemsA}" DeSelectedItems="{Binding DeSelectedItemsA}" Width="300" Height="300"/>

Regarding the DataContext, the control template does not appear to require the DataContext specifically set as the ViewModel is implicitly bound to the parent view and therefore to this control, I have verified this while debugging.

I do have the control working as intended but only tested as a single instance at the moment, I will test with mutiple instances to enable me to fix the single list instance issue you have kindly pointed out.

Once again, thanks for your time.

Just racking up the postings

SledgeHammer013-Dec-10 14:33

3-Dec-10 14:33

Ok... So, what you are initially doing is having every instance of your control share the same instance of ObservableCollection. However, you do allow the user to overwrite said instance through your property setter. That will cause you *many* problems down the road with data binding. One area where WPF crumbles hard is when you start switching around instances of objects or creating temporary objects, etc. because it depends on those being the same object to function.

Now, C# doesn't have pointers, but I will use them to illustrate what I am trying to explain.

1) you create your control, your control creates an ObservableCollection() [0x1000]
2) a user of your control subscribes to [0x1000].CollectionChanges
3) a user calls your setter with a new ObservableCollection() [0x2000]

Guess what happened? Everybody subscribing to the [0x1000] collection events is now broken. Everybody making changes to the [0x1000] collection is broken as well. [0x1000] is now orphaned.

What you want is for each instance of your control to create its own ObservableCollection and *NEVER* let anybody change that. It is important that if you created [0x1000], that it remains [0x1000] for the lifetime of your control. Otherwise bad things will happen.

Now, the read-only DP will not fulfil your just mentioned requirement of binding to collections. Fair enough.

What you are trying to do here is combining TWO techniques into ONE which will cause you the problems just mentioned.

If you look at the ListView or TreeView for example, you will see the proper way to lay out your control.

public ObservableCollection<???> Items // this *MUST* be read-only
{
get { ... }
}

public IEnumerable ItemsSource /// this is how people will pass in collections
{
get { ... }
set { ... }
}

So what happens here is that people can add items manually to the Items collection OR use the ItemsSource to pass in collections.

If you only need to allow passing in collections, use the IEnumerable ItemsSource method instead.

If you want to support both, you need to add some "protection" code...

i.e. don't allow use of Items if ItemsSource is not null and vice versa, etc.

vs 2010 settings

arkiboys1-Dec-10 21:43

1-Dec-10 21:43

Hi,

I am building a silverlight app in vs2010 premium edition.
I do not seem to be able to find the option where I can change the windows from the default tabs to mdi windows.

Any thoughts please?

Re: vs 2010 settings

Abhinav S1-Dec-10 22:34

Abhinav S

1-Dec-10 22:34

You could have done better to post this question in the Visual Studio section[^].

However, for your answer, just double clicking on the window should make it 'float'.
Or you could right click on the code window title bar and select 'float'.

The funniest thing about this particular signature is that by the time you realise it doesn't say anything it's too late to stop reading it.

My latest tip/trick

Visit the Hindi forum here.

Re: vs 2010 settings

arkiboys1-Dec-10 23:54

1-Dec-10 23:54

Solved.
Thank you.

GUI guidance

arkiboys1-Dec-10 21:35

1-Dec-10 21:35

I am in the process of building a monitoring application for the daily import processes...
The app should check the status of the services running on various servers.
It should also keep track of the errors, frequency of loads, etc.
So basically it acts like an admin/control page.
Can you recommend a UI for me to look at so that I can get a feel of what the UI should look like to cater for such requirements ?

Regards

Re: GUI guidance

phil.o3-Dec-10 0:09

phil.o

3-Dec-10 0:09

Nagios / Centreon would be a good start obviously.

Re: GUI guidance

arkiboys3-Dec-10 1:48

How do I Invalidate or repaint the Window in WPF.

3-Dec-10 1:48

Do not understand what you mean.
Please explain.
Thanks

Re: GUI guidance

phil.o4-Dec-10 2:46

phil.o

4-Dec-10 2:46

arkiboys wrote:
Can you recommend a UI for me to look at so that I can get a feel of what the UI should look like to cater for such requirements ?

I was just answering your question Smile | :)

Nagios is a web solution to monitor servers and services accross networks ; Centreon is a web interface to configure Nagios. If you are searching for ideas about UI design with such requirements, you should take a look at these products.

o1010wanabe1-Dec-10 12:25

o1010wanabe

1-Dec-10 12:25

I have code that leaves garbage on the window. need to rePaint .
couldnt find an invalidate that I knew how to use.

I probably clean up nice.

Re: How do I Invalidate or repaint the Window in WPF.

SledgeHammer012-Dec-10 6:22