问题
Little problem with my Android application and I don't know how to solve it with MVVM Cross.
Here is my Model
public class Article
{
string Label{ get; set; }
string Remark { get; set; }
}
My ViewModel
public class ArticleViewModel: MvxViewModel
{
public List<Article> Articles;
....
}
My layout.axml ...
<LinearLayout
android:layout_width="0dip"
android:layout_weight="6"
android:layout_height="fill_parent"
android:orientation="vertical"
android:id="@+id/layoutArticleList">
<EditText
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:id="@+id/editSearch"
android:text=""
android:singleLine="True"
android:selectAllOnFocus="true"
android:capitalize="characters"
android:drawableLeft="@drawable/ic_search_24"
local:MvxBind="{'Text':{'Path':'Filter','Mode':'TwoWay'}}"
/>
<Mvx.MvxBindableListView
android:id="@+id/listviewArticle"
android:choiceMode="singleChoice"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
local:MvxItemTemplate="@layout/article_rowlayout"
local:MvxBind="{'ItemsSource':{'Path':'Articles'}}" />
</LinearLayout>
...
And here comes my problem, the "article_rowlayout"
...
<TableRow
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="@color/blue">
<TextView
android:id="@+id/rowArticleLabel"
android:layout_width="0dip"
android:layout_weight="14"
android:layout_height="wrap_content"
android:textSize="28dip"
local:MvxBind="{'Text':{'Path':'Label'}}" />
<ImageButton
android:src="@drawable/ic_modify"
android:layout_width="0dip"
android:layout_weight="1"
android:layout_height="wrap_content"
android:id="@+id/rowArticleButtonModify"
android:background="@null"
android:focusable="false"
android:clickable="true"
local:MvxBind="{'Click':{'Path':'MyTest'}}"
/>
...
The "Click" command called "MyTest" is linked on the item given by the MvxBindableListView. In other words, Click search for a command "MyTest" in my model "Article", instead of my ViewModel. How can I change that behaviour in order to link my ViewModel "ArticleViewModel" which is responsible of my MvxBindableListView?
Any suggestions?
回答1:
Your analysis is definitely correct about where the click event is trying to bind.
There are two approaches I generally take:
- Use ItemClick on the List
- Continuing using Click but do some redirection on the ViewModel side.
So...1
The Main Menu in the tutorial has a ViewModel a bit like:
public class MainMenuViewModel
: MvxViewModel
{
public List<T> Items { get; set; }
public IMvxCommand ShowItemCommand
{
get
{
return new MvxRelayCommand<T>((item) => /* do action with item */ );
}
}
}
This is used in axml as:
<Mvx.MvxBindableListView
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:local="http://schemas.android.com/apk/res/Tutorial.UI.Droid"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
local:MvxBind="{'ItemsSource':{'Path':'Items'},'ItemClick':{'Path':'ShowItemCommand'}}"
local:MvxItemTemplate="@layout/listitem_viewmodel"
/>
This approach can only be done for ItemClick on the whole list item - not on individual subviews within the list items.
Or...2
Since we don't have any RelativeSource binding instructions in mvx, this type of redirection can be done in the ViewModel/Model code.
This can be done by presenting a behaviour-enabled wrapper of the Model object rather than the Model object itself - e.g. using a List<ActiveArticle>:
public ActiveArticle
{
Article _article;
ArticleViewModel _parent;
public WrappedArticle(Article article, ArticleViewModel parent)
{
/* assignment */
}
public IMvxCommand TheCommand { get { return MvxRelayCommand(() -> _parent.DoStuff(_article)); } }
public Article TheArticle { get { return _article; } }
}
Your axml would then have to use bindings like:
<TextView ...
local:MvxBind="{'Text':{'Path':'TheArticle.Label'}}" />
and
<ImageButton
...
local:MvxBind="{'Click':{'Path':'TheCommand.MyTest'}}" />
One example of this approach is the Conference sample which uses WithCommand
However... please note that when using WithCommand<T> we discovered a memory leak - basically the GarbageCollection refused to collect the embedded MvxRelayCommand - which is why WithCommand<T> is IDisposable and why BaseSessionListViewModel clears the list and disposes the WithCommand elements when views are detached.
Update after comment:
If your data list is large - and your data is fixed (your articles are models without PropertyChanged) and you don't want to incur the overhead of creating a large List<WrappedArticle> then one way around this might be to use a WrappingList<T> class.
This is very similar to the approach taken in Microsoft code - e.g. in virtualizing lists in WP7/Silverlight - http://shawnoster.com/blog/post/Improving-ListBox-Performance-in-Silverlight-for-Windows-Phone-7-Data-Virtualization.aspx
For your articles this might be:
public class ArticleViewModel: MvxViewModel
{
public WrappingList<Article> Articles;
// normal members...
}
public class Article
{
public string Label { get; set; }
public string Remark { get; set; }
}
public class WrappingList<T> : IList<WrappingList<T>.Wrapped>
{
public class Wrapped
{
public IMvxCommand Command1 { get; set; }
public IMvxCommand Command2 { get; set; }
public IMvxCommand Command3 { get; set; }
public IMvxCommand Command4 { get; set; }
public T TheItem { get; set; }
}
private readonly List<T> _realList;
private readonly Action<T>[] _realAction1;
private readonly Action<T>[] _realAction2;
private readonly Action<T>[] _realAction3;
private readonly Action<T>[] _realAction4;
public WrappingList(List<T> realList, Action<T> realAction)
{
_realList = realList;
_realAction = realAction;
}
private Wrapped Wrap(T item)
{
return new Wrapped()
{
Command1 = new MvxRelayCommand(() => _realAction1(item)),
Command2 = new MvxRelayCommand(() => _realAction2(item)),
Command3 = new MvxRelayCommand(() => _realAction3(item)),
Command4 = new MvxRelayCommand(() => _realAction4(item)),
TheItem = item
};
}
#region Implementation of Key required methods
public int Count { get { return _realList.Count; } }
public Wrapped this[int index]
{
get { return Wrap(_realList[index]); }
set { throw new NotImplementedException(); }
}
#endregion
#region NonImplementation of other methods
public IEnumerator<Wrapped> GetEnumerator()
{
throw new NotImplementedException();
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
public void Add(Wrapped item)
{
throw new NotImplementedException();
}
public void Clear()
{
throw new NotImplementedException();
}
public bool Contains(Wrapped item)
{
throw new NotImplementedException();
}
public void CopyTo(Wrapped[] array, int arrayIndex)
{
throw new NotImplementedException();
}
public bool Remove(Wrapped item)
{
throw new NotImplementedException();
}
public bool IsReadOnly { get; private set; }
#endregion
#region Implementation of IList<DateFilter>
public int IndexOf(Wrapped item)
{
throw new NotImplementedException();
}
public void Insert(int index, Wrapped item)
{
throw new NotImplementedException();
}
public void RemoveAt(int index)
{
throw new NotImplementedException();
}
#endregion
}
来源：https://stackoverflow.com/questions/12682082/mvvmcross-changing-viewmodel-within-a-mvxbindablelistview