Develop Reference

Making a dynamic set of 3 pickers on Xamarin.Forms

we are developing a cross platform app on Xamarin.Forms.
On one of the pages we need to display a set of 3 pickers with the same list of items. The idea is that when you select an item on one of the pickers it gets removed from the item-source of the other two.
To do this we developed the following code:
We started with a list of Items called BaseList which we get from a web service. We also create 3 separate lists (ListA, ListB and ListC) and 3 Items to store the selected Items of each picker (SelectedA, SelectedB and SelectedC).
private List<Item> BaseList;
private List<Item> _ListA;
private Item _SelectedA;
private List<Item> _ListB;
private Item _SelectedB;
private List<Item> _ListC;
private Item _SelectedC;
…
//Api Calls
private void LoadData()
{
…
BaseList = new List<Item> (ListFromWebServices);
_ListA = new List<Item>(BaseList);
OnPropertyChanged(nameof(ListA));
_ListB = new List<Item>(BaseList);
OnPropertyChanged(nameof(ListB));
_ListC = new List<Item>(BaseList);
OnPropertyChanged(nameof(ListC));
}
…
//Public Fields
public List<Item> ListA
{
get
{
return _ListA;
}
}
public Item SelectedA
{
get
{
return _SelectedA;
}
set
{
SetProperty(ref _SelectedA, value, nameof(SelectedA));
}
}
public List<Item> ListB
{
get
{
return _ListB;
}
}
public Item SelectedB
{
get
{
return _SelectedB;
}
set
{
SetProperty(ref _SelectedB, value, nameof(SelectedB));
}
}
public List<Item> ListC
{
get
{
return _ListC;
}
}
public Item SelectedC
{
get
{
return _SelectedC;
}
set
{
SetProperty(ref _SelectedC, value, nameof(SelectedC));
}
}
This code is on our ViewModel, so we use SetProperty to set the referenced property to the value and invoke PropertyChangedEventArgs from INotifyPropertyChanged
public event PropertyChangedEventHandler PropertyChanged;
protected bool SetProperty<T>(ref T storage, T value,
[CallerMemberName] string propertyName = null)
{
if (Equals(storage, value))
return false;
storage = value;
OnPropertyChanged(propertyName);
return true;
}
protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
In order to update the ItemSource's, whenever a selected item is changed we call OnSelectedItemChanged from the setters of SelectedA, SelectedB and SelectedC. This method receives an index which indicates which Picker triggered it:
private void OnSelectedItemChanged(int index)
{
Item CurrentA = SelectedA;
Item CurrentB = SelectedB;
Item CurrentC = SelectedC;
int i;
switch (index)
{
case 0:
_ListB = new List<Item> (BaseList);
_ListB.Remove(CurrentA);
_ListB.Remove(CurrentC);
OnPropertyChanged(nameof(ListB));
_ListC = new List<Item>(BaseList);
_ListC.Remove(CurrentA);
_ListC.Remove(CurrentB);
OnPropertyChanged(nameof(ListC));
i = ListB.IndexOf(CurrentB);
if (i > -1)
{
_SelectedB = ListB[i];
}
OnPropertyChanged(nameof(SelectedB));
i = ListC.IndexOf(CurrentC);
if (i > -1)
{
_SelectedC = ListC[i];
}
OnPropertyChanged(nameof(SelectedC));
break;
case 1:
_ListA = new List<Item>(BaseList);
_ListA.Remove(CurrentB);
_ListA.Remove(CurrentC);
OnPropertyChanged(nameof(ListA));
_ListC = new List<Item>(BaseList);
_ListC.Remove(CurrentA);
_ListC.Remove(CurrentB);
OnPropertyChanged(nameof(ListC));
i = ListA.IndexOf(CurrentA);
if (i > -1)
{
_SelectedA = ListA[i];
}
OnPropertyChanged(nameof(SelectedA));
i = ListC.IndexOf(CurrentC);
if (i > -1)
{
_SelectedC = ListC[i];
}
OnPropertyChanged(nameof(SelectedC));
break;
case 2:
_ListA = new List<Item>(BaseList);
_ListA.Remove(CurrentB);
_ListA.Remove(CurrentC);
OnPropertyChanged(nameof(ListA));
_ListB = new List<Item>(BaseList);
_ListB.Remove(CurrentA);
_ListB.Remove(CurrentC);
OnPropertyChanged(nameof(ListB));
i = ListA.IndexOf(CurrentA);
if (i > -1)
{
_SelectedA = ListA[i];
}
OnPropertyChanged(nameof(SelectedA));
i = ListB.IndexOf(CurrentB);
if (i > -1)
{
_SelectedB = ListB[i];
}
OnPropertyChanged(nameof(SelectedB));
break;
}
}
What we do here is basically save the current selected item for each picker on a separate variable, copy the BaseList into the two pickers that didn't call the event, then on the each new list remove all the options in use by the other pickers, set again the selected Item on each new list to the one that was selected originally and finally call OnPropertyChanged() to inform the views of the change.
The issue here is that when we change the ItemSource on a Picker it sets the SelectedItem to null. calling OnPropertyChanged() on the setter after OnSelectedItemChanged()was called leads to an infinite loop of one Picker updating the other, and adding a filter that checks if the value isn't null before setting it makes the Picker display no selected item, while the value is already set.

just in case anyone has the same issue, we found a solution for this. Turns out if you make CurrentA, CurrentB and CurrentC global variables and add on each case an if ((CurrentA != SelectedA) && (!(SelectedA is null))) { ... (do all the stuff) } break; and at the end you set
_SelectedA = CurrentA;
OnPropertyChanged(nameof(SelectedA));
_SelectedB = CurrentB;
OnPropertyChanged(nameof(SelectedB));
_SelectedC = CurrentC;
OnPropertyChanged(nameof(SelectedC));
it works. We don't know why tho :)

Add ToolTip to "Word" in a context menu

I want to add a tooltip to a menu item. On the menu there is the word "DELETE" and when the mouse hovers over the word I want a tooltip displayed. I though of using 'ToolTipService.SetToolTip();'.
This is where the items contained in the menu are set...
protected virtual void SetContextMenuItems()
{
// -- Add condition for ReadOnly + ReadOnly Attribute to AreaEntity
if (this.ViewMode == Common.Core.ViewModes.RealTime)
{
AreaEntity ae = viewModel.EntityViewContext as AreaEntity;
if (((UserContext.Instance.IsAdmin() && (ae.Scope.Value == "global" || ae.Scope.Value == string.Empty)) ||
ae.OwnerPosition.Value == CoreServices.Instance.CurrentPosition.Configuration.Name)
&& !((this.MapInstance.Parent as Grid).Parent is PIPMap))
{
menuItem = new ContextMenuItem();
//menuItem.DisplayText = "Delete"; // -- Could be dynamic based off type "Edit Polygon (Circle, etc.)"
menuItem.DisplayText = CoreServices.Instance.GetString("Delete");
cmd = new MR.CommandBridge.Common.Command.DelegateCommand(DeleteShape, CanDelete);
menuItem.Command = cmd;
this.ContextMenu.MenuItems.Add(menuItem);
}
}
}
Methods 'DeleteShape' and 'CanDelete':
public void DeleteShape(object param)
{
EntityStore.Instance.DeleteEntity(this.ViewModel.EntityViewContext);
}
public bool CanDelete(object param)
{
GetRulesForShape();
bool isInFilter = false;
EntityCollection<Entity> lists = EntitySync.Instance.Cache["entityCollection"];
foreach (Entity list in lists)
{
isInFilter = (list as ListEntity).FilterList.Filters.Count(a => (a.FilterType == FilterTypes.WithinZone && a.Value == this.viewModel.EntityViewContext.Uri) ||
(a.FilterType == FilterTypes.MultipleFilter && a.Filters.Count(b => b.FilterType == FilterTypes.WithinZone && b.Value == this.viewModel.EntityViewContext.Uri) > 0)) > 0;
if (isInFilter) break;
}
return !HasRules && !CoreServices.Instance.ZoneFilters.Contains(this.viewModel.Area.Uri) && gfEditor.dm != GeofenceEditor.DrawMode.DrawEdit && !isInFilter;
}

Ok I made some adjustments to your class.
Somehow I got the feeling your mixing up things like control and bindings.
We'll see. ;)
I've also made some comments, maybe you can shed some light over then.
public class ContextMenuItem : MenuItem
{
public ContextMenuItem()
:base()
{
}
//Replace by Header
//
//public string DisplayText { get; set; }
//Can this be replaced by build in CommandParameter
//
private Dictionary<string, object> _parameters = new Dictionary<string, object>();
private Func<ContextMenuItem, List<ContextMenuItem>> _getMenuItems = null;
//Already available
//public DelegateCommand Command { get; set; }
//What does this function do?
public Func<ContextMenuItem, List<ContextMenuItem>> GetMenuItems
{
get
{
return _getMenuItems;
}
set
{
_getMenuItems = value;
}
}
public Dictionary<string, object> Parameters
{
get
{
return _parameters;
}
}
//Can be replaced by base Items
//
//private List<ContextMenuItem> _menuItems = new List<ContextMenuItem>();
//public List<ContextMenuItem> ChildMenuItems
//{
// get
// {
// return _menuItems;
// }
//}
private bool _isChecked = false;
public bool IsChecked
{
get { return _isChecked; }
set { _isChecked = value; }
}
// -- Command or implementer could provide a handler for all commands - might be simpler for now
// -- I think there could be a better way to route commands but I'll thin on it.

Could this simply be done in .css?
.yourclass:hover{
cursor:pointer;
}
or target it with jquery?

Have you tried this?
menuitem.ToolTip = "Delete";
Normally a contextmenu can exist of regular MenuItems. I used it often.
;)

Context menu items have the ToolTipText property:
menuItem.ToolTipText = "ToolTip Text Here";

use string value of mvvm message as variable in viewmodel

I'm filtering a listcollectionview in viewModel 1 based on selectionchanged of datagrid in viewModel 2. To do this I use mvvm messaging. Each time the selection of the datagrid changes a message is send to update my listcollectionview. This all works well.
Now I need to use the string value of this message to pass into the filter. The problem is that I can only use the string value in the updateShotList method but not into the bool IsMatch. How can I make this work, or how can I use the string value of the message as a variable in my viewmodel.
This is how my viewmodel looks like.
private ObservableCollection<Shot> _allShots = new ObservableCollection<Shot>();
public ObservableCollection<Shot> AllShots
{
get { return _allShots; }
set { _allShots = value; RaisePropertyChanged();}
}
private ListCollectionView _allShotsCollection;
public ListCollectionView AllShotsCollection
{
get
{
if (_allShotsCollection == null)
{
_allShotsCollection = new ListCollectionView(this.AllShots);
}
return _allShotsCollection;
}
set
{
_allShotsCollection = value; RaisePropertyChanged();
}
}
private void UpdateShotList(string SceneNr) // value sceneNr comes from message from viewmodel 2
{
_allShotsCollection.IsLiveFiltering = true;
_allShotsCollection.Filter = new Predicate<object>(IsMatchFound);
}
bool IsMatchFound(object obj)
{
=====> if (obj as Shot != null && (obj as Shot).SceneNumber == "?????") // Here I need the value of string ScenNr that comes from the message.
{
return true;
}
return false;
}
public ShotListViewModel()
{
Messenger.Default.Register<string>(this, "UpdateShotList", UpdateShotList);
}

You can create your predicate as a lambda expression and close over SceneNr to capture it:
_allShotsCollection.Filter = o =>
{
var shot = o as Shot;
return shot != null && shot.SceneNumber == SceneNr;
};
Alternatively, simply introduce an instance variable to contain your filter string and update it each time you receive a message:
private string _sceneNr;
private void UpdateShotList(string sceneNr)
{
// ...
_sceneNr = sceneNr;
}
bool IsMatchFound(object obj)
{
var shot = obj as Shot;
return shot != null && shot.SceneNumber == _sceneNr;
}

Filter a property by the value of another property

I have two drop down lists. Niether of them have a relation ship with each other. But I need to filter one drop down list based on the chosen value of another drop down list.
I can filter it in code. When I debug I can see the filtered results on the property. However when I run the app, it does not work. Here is my code so far:
private BindingList<Commodity> _AllocationCommodities;
[Browsable(false)]
public BindingList<Commodity> AllocationCommodities
{
get
{
if (_AllocationCommodities == null)
{
_AllocationCommodities = new BindingList<Commodity>();
ChangeCommodities();
}
return _AllocationCommodities;
}
}
private SourceEntity _SourceEntity;
[ImmediatePostData]
[Association("SourceEntity-LimitAllocations")]
[RuleRequiredField("RuleRequiredField_LimitAllocation_SourceEntity", DefaultContexts.Save)]
public SourceEntity SourceEntity
{
get
{
return _SourceEntity;
}
set
{
//New Code
if (SetPropertyValue<SourceEntity>("SourceEntity", value))
{
if (IsSaving || IsLoading) return;
ChangeCommodities();
}
}
}
private Commodity _Commodity;// This is the drop down to be filtered
[ImmediatePostData]
[DataSourceProperty("AllocationCommodities")] //// This Attribute Should filter Commodities
[RuleRequiredField("RuleRequiredField_LimitAllocation_Commodity", DefaultContexts.Save)]
public Commodity Commodity
{
get
{
return _Commodity;
}
set
{
SetPropertyValue("Commodity", ref _Commodity, value);
if (Commodity.Oid != Guid.Empty)
AllocationVolumeUnits.Reload();
}
}
private void ChangeCommodities()
{
if (!this.IsLoading && _SourceEntity != null)
{
_AllocationCommodities.RaiseListChangedEvents = false;
_AllocationCommodities.Clear();
OperandValue[] _params;
System.Collections.Generic.List<CMSBOD.SourceCommodity> _sc = new System.Collections.Generic.List<SourceCommodity>();
BindingList<Commodity> _Commodities = new BindingList<Commodity>();
foreach (SourceCommodityEntity _tempSCE in _SourceEntity.SourceCommodityEntities)
{
if (_tempSCE.SourceCommodity != null)
_sc.Add(_tempSCE.SourceCommodity);
}
foreach (SourceCommodity _tempSC in _sc)
{
if (_tempSC.Commodity != null && !_Commodities.Contains<Commodity>(_tempSC.Commodity) && _tempSC.Commodity.IsActive)
_Commodities.Add(_tempSC.Commodity);
}
_AllocationCommodities.RaiseListChangedEvents = true;
_AllocationCommodities = _Commodities;///This is where I can see the filtered list when debugging.
}
}

You can find a DataSourceCriteria useful in this scenario, instead of DataSourceProperty.
Assuming you have collection properties that associates Commodity back to SourceCommodityEntity, you can use this criteria:
[DataSourceCriteria("IsActive And SourceCommodities[SourceCommodityEntities[SourceEntity = '#SourceEntity'] ]")]
Even if its designed to be a 1x1 assocation, you can find that associations can be useful for filtering purposes.

NotifyPropertyChanged of a Calculated property when Items in List Changes

I Have a model SupplierInvoice as follows:
public class SupplierInvoice
{
public bool Use { get; set; }
public ApInvoice Invoice { get; set; }
}
And a ViewModel with a list of this model:
private List<SupplierInvoice> _SupplierInvoices;
public List<SupplierInvoice> SupplierInvoices
{
get
{
return this._SupplierInvoices;
}
set
{
if (this._SupplierInvoices != value)
{
this._SupplierInvoices = value;
this.RaisePropertyChanged("SupplierInvoices");
}
}
}
within this ViewModel I have a calculated property too:
public decimal ApTotal
{
get
{
decimal total = 0;
if (this.SupplierInvoices != null)
{
foreach (SupplierInvoice invoice in this.SupplierInvoices)
{
if (invoice.Use)
{
total += invoice.Invoice.MthInvBal1;
}
}
}
return total;
}
}
this calculated property returns the sum of the balance of all the invoices (if the invoice's Use property is true). The Use property is selected to be true on the view with a checkbox in a grid.
Now... the question is: How do I NotifyPropertyChanged of this calculated property (ApTotal) when the Use property of the SupplierInvoice model has been changed?

I think replacing your List<TObject> by an ObservableCollection<TObject> will do the trick.
From what I remember the List isn't propagating the PropertyChangedEvent to the UI thread.

This may be a bit naughty, but you could always do this:
private List<SupplierInvoice> _SupplierInvoices;
public List<SupplierInvoice> SupplierInvoices
{
get
{
return this._SupplierInvoices;
}
set
{
if (this._SupplierInvoices != value)
{
this._SupplierInvoices = value;
this.RaisePropertyChanged("SupplierInvoices");
this.RaisePropertyChanged("ApTotal");
}
}
}

Whenever you have a calculated property, you just need to raise the INotifyPropertyChanged.PropertyChanged event from the other properties that are involved in the calculation. So as your ApTotal property is calculated from just the SupplierInvoices property, then you can just notify the interface from that property setter:
public List<SupplierInvoice> SupplierInvoices
{
get
{
return this._SupplierInvoices;
}
set
{
if (this._SupplierInvoices != value)
{
this._SupplierInvoices = value;
this.RaisePropertyChanged("SupplierInvoices");
this.RaisePropertyChanged("ApTotal");
}
}
}