CODEWITHSUNDEEP
xamlmvvmwindows-runtimewinrt-xaml
webdad3
webdad3

Reputation: 9080

MVVM - Summary/Detail

So I'm trying to wrap my head around MVVM and I'm finding that I have more questions than answers. The tutorials don't go far enough for me when it comes to the next step...

Basically I want a list of items and then a way to get the detail of each item.

Below is the examples that I've found online and they work great for displaying the list, but I need to know how I can use my VM to get the detail of this item.

private IList<item> m_items;
private IList<item> m_Item;


private IList<item> getItemDetail(Int32 iId)
{
    var myItem =
        from i in items
        where i.iId == iId
        select i;

    m_Item = new List<item>();
    foreach (var item in myItem)
    {
        m_Item.Add(item);
    }
    return m_Item;
}

public myViewModel()
{

    m_items = new List<item>
    {        
    new item(1, "test,),
    new item(2, "test2"),
    new item(3, "test1")
    };

    m_Item = new List<item>();
    m_Item = getItemDetail(iId);

}

Update:

I updated my View Model code above. I think what I've done is I have added another List where when the user navigates to a detail page the view model gets called with the specific ID which then populates the detail List. I probably don't need a list here but I wanted to try to keep it consistent with the main page code.

In my detail page I'm setting up the VM this way:

    itemViewModel VM = new itemViewModel((Int32)navigationParameter);
    DataContext = VM;

When I break on the VM variable I see my 2 lists. However, my binding doesn't work on the XAML. If I need to post some sample XAML let me know. I can do that but I'm hoping there is something I'm missing here.

I'm trying to learn MVVM and I want to do things right. So instead of continuing down a wrong path I would really like to know the "right" way of doing things. So if you see errors, please let me know.

Thanks!

Upvotes: 0

Views: 429

Answers (2)

Darkside
Darkside

Reputation: 1739

right, i'd suggest you go back to basics first and watch Laurent's Mix sessions about MVVM, you find links to then from the mvvmlight site on codeplex.

but to break it down you've hit a few of the hurdles I did when I first started.

1: (the biggest gotcha) for databinding to work, you must expose data using a property (get and set pattern), just a list variable won't work. this goes for everything you want to bind to. The alternative is to set item sources directly in code but you will loose all the features of databinding, including updates.

2: to understand databinding you need to understand the INotifyProperty changed pattern, this is the underlying gubbins (technical term ;-D) to enable binding to work properly. as suggested start a new "master/details" project template and walk through it, from the viewmodels holding the data to the views (pages) looking at the data in the view model

3: use observablecollections for lists, they are just better for binding and are basically just lists with extras

4: remember you can also bind the "selecteditem" or "selectedindex" of a listbox to capture what the user has selected, just be sure to set the binding to "twoway" so the view can push data to the viewmodel and not just read, like this: {binding myselecteditem, mode="twoway"}

hope this helps but if your still stuck Laurents videos are the best, just watch them a few times and follow what he does line by line

Upvotes: 2

aleph_null
aleph_null

Reputation: 5786

I believe you want to use what Microsoft calls the "master-detail binding scenario", where several controls bind to a single collection or to its selected item. To do so, you need to bind to a so called collection view, which is just a layer on top of the collection used by WPF. For instance, you can bind a ListBox's ItemSource and a ContentControl's Content to the same collection view, and the ContentControl will display the details of the the ListBox's selected item.

see: http://msdn.microsoft.com/en-us/library/ms752347.aspx#master_detail_scenario

P.S. you may want to use an ObservableCollection instead of a List, and make sure your view model implements INotifyPropertyChanged.

Upvotes: 1

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