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POWPF/MVVM: Weird behaviour of wpf buttons with Commands disabling
 

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  1. POWPF/MVVM: Weird behaviour of wpf buttons with Commands disabling
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    <p>just some code...: <strong>Question is at bottom.</strong></p> <p><strong>XAML</strong>:</p> <pre><code> &lt;StackPanel Orientation="Horizontal"&gt; &lt;Button Content="Start" Command="{Binding FirstDateCommand}" /&gt; &lt;Button Content="Back" Command="{Binding PreviousDateCommand}" /&gt; &lt;DatePicker SelectedDate="{Binding SelectedDate}" DisplayDateStart="{Binding MinDate}" DisplayDateEnd="{Binding MaxDate}" /&gt; &lt;Button Content="Forward" Command="{Binding NextDateCommand}" /&gt; &lt;Button Content="End" Command="{Binding LastDateCommand}" /&gt; &lt;/StackPanel&gt; </code></pre> <p><strong>ViewModel</strong>:</p> <pre><code>public class LessonPlannerViewModel : ViewModelBase { private ILessonPlannerRepository _lessonplannerRepo; private ObservableCollection&lt;LessonDay&gt; _lessons; private RelayCommand _firstDateCommand; private RelayCommand _lastDateCommand; private RelayCommand _nextDateCommand; private RelayCommand _previousDateCommand; public LessonPlannerViewModel() { _lessonplannerRepo = new LessonPlannerRepository(); MinDate = DateTime.Now.AddDays(-2); MaxDate = DateTime.Now.AddDays(2); SelectedDate = DateTime.Now; } public RelayCommand FirstDateCommand { get { return _firstDateCommand ?? (_firstDateCommand = new RelayCommand(() =&gt; MoveFirstDate(), () =&gt; CanMoveFirstDate())); } } public RelayCommand LastDateCommand { get { return _lastDateCommand ?? (_lastDateCommand = new RelayCommand(() =&gt; MoveLastDate(), () =&gt; CanMoveLastDate())); } } public RelayCommand PreviousDateCommand { get { return _previousDateCommand ?? (_previousDateCommand = new RelayCommand(() =&gt; MovePreviousDate(), () =&gt; CanMovePreviousDate())); } } public RelayCommand NextDateCommand { get { return _nextDateCommand ?? (_nextDateCommand = new RelayCommand(() =&gt; MoveNextDate(), () =&gt; CanMoveNextDate())); } } private void MoveFirstDate() { SelectedDate = MinDate; Lessons = _lessonplannerRepo.GetLessonDayByDate(SelectedDate); } private void MoveLastDate() { SelectedDate = MaxDate; Lessons = _lessonplannerRepo.GetLessonDayByDate(SelectedDate); } private void MoveNextDate() { SelectedDate = SelectedDate.AddDays(1); Lessons = _lessonplannerRepo.GetLessonDayByDate(SelectedDate); } private void MovePreviousDate() { SelectedDate = SelectedDate.AddDays(-1); Lessons = _lessonplannerRepo.GetLessonDayByDate(SelectedDate); } private bool CanMoveFirstDate() { return SelectedDate != MinDate; } private bool CanMoveLastDate() { return SelectedDate != MaxDate; } private bool CanMoveNextDate() { return SelectedDate &lt; MaxDate; } private bool CanMovePreviousDate() { return SelectedDate &gt; MinDate; } private DateTime _selectedDate; public DateTime SelectedDate { get { return _selectedDate; } set { if (_selectedDate == value) return; _selectedDate = value; this.RaisePropertyChanged("SelectedDate"); //Lessons = _lessonplannerRepo.GetLessonDayByDate(SelectedDate); } } public DateTime MinDate { get; set; } public DateTime MaxDate { get; set; } public ObservableCollection&lt;LessonDay&gt; Lessons { get { return _lessons; } set { _lessons = value; this.RaisePropertyChanged("Lessons"); } } ... </code></pre> <p>When I choose in the DatePicker a date which is equal to MinDate then the PreviousDateCommand returns CanExecute = false; t<strong>hats ok and works as expected</strong>.</p> <p>But why is the LastDateCommand <strong>not returning CanExecute = false too?</strong> </p> <p>My CanExecute logic works as expected, when I press the <strong>PreviousDateButton</strong> <em>instead</em> of selecting the date via <strong>datepicker</strong>.</p> <p>What do I wrong?</p> <p><strong>UPDATE</strong>:</p> <p>I have not had any doubts that my logic is wrong but... I tried some things and with this code</p> <p>this is really weird. I changed now the logic of the LastDate and PreviousDate CanExecute method and both buttons work now changing the datepicker.</p> <pre><code>private bool CanMoveFirstDate() { Debug.WriteLine("SelectedDate FirstDate: " + SelectedDate); return SelectedDate &gt; MinDate; } private bool CanMovePreviousDate() { Debug.WriteLine("SelectedDate PreviousDate: " + SelectedDate); return SelectedDate &gt; MinDate; } </code></pre> <p>Is someone knows how to make the NextDate + LastDate button working gets the solution! :P</p> <p><strong>UPDATE 2:</strong></p> <p>Bindings are powerfull but maybe hard to control...</p> <p>I did some crazy logic shit again and now it seems to work:</p> <pre><code> private bool CanMoveNextDate() { Debug.WriteLine("SelectedDate NextDate: " + SelectedDate); return SelectedDate.AddDays(1) &lt; MaxDate; } private bool CanMoveLastDate() { Debug.WriteLine("SelectedDate LastDate: " + SelectedDate); return SelectedDate.AddDays(1) &lt; MaxDate; } </code></pre> <p>If someone can <strong>explain</strong> that weird logic, that would be nice , I think the cause lays in the binding of the datepicker and the commands and which binding gets updated first or is called etc...</p>
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    1. COI'm not sure I understand the question, you seem to be saving that when the selected date == MinDate, PreviousDateCommand.CanExecute() returns false and LastDateCommand.CanExecute() returns true, which sounds right. What's the issue, is it different behaviour depending on whether the date is picked using the DatePicker vs the buttons?
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      1. POWPF/MVVM: Weird behaviour of wpf buttons with Commands disabling
      1. USGrant Crofton
    2. CO"...is it different behaviour depending on whether the date is picked using the DatePicker vs the buttons?" => YES, it is different except for the PreviousDateCommand, that works choosing the datepicker.
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      1. USmsfanboy
    3. CO@msfanboy: If LastDateCommand is creating the issue, then you should counter-check the result with that of LastDateButton and not PreviousDateButton which is already working fine. Despite that the issue seems weird. What does the debugger say?
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      1. POWPF/MVVM: Weird behaviour of wpf buttons with Commands disabling
      1. USAmsakanna
 

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