在加載時獲取實際高度

Question

我正在為數據網格創建用戶控件。 該數據網格具有一些新舊條目。 要求新條目顯示在屏幕頂部，但數據順序必須是按時間順序排列的。 因此，我通過添加空行將整個網格向上推。 例如，如果我有8個舊條目和2個新條目，則必須將8個舊條目“隱藏”在兩個新條目中的第一個之上。

要計算空行，我想將用戶控件的實際高度除以行高。 我找到了一種通過依賴項屬性獲取實際高度的方法（請參見下面的代碼）。 我一開始需要它可用，因此我實現了一個觸發器以使我能夠訪問load事件。 但是此時用戶控件的大小仍為0。那么是否還有另一個事件可以讓我根據正確的時間進行計算？

最后一點，我正在使用Galasoft MVVMLight和匹配的mvvm模式。 同樣，在您首次初始化后更改窗口的高度后，dependency屬性的確會提供正確的高度。

風景

<DataGrid x:Class="Kwa.Presentation.Views.AlarmList.AlarmList"
          xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
          xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
          xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
          xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
          xmlns:local="clr-namespace:Kwa.Presentation.Views.AlarmList"
          xmlns:behaviors="clr-namespace:Kwa.Presentation.Behaviors"
          xmlns:Trans="clr-namespace:Kwa.Presentation.Resources"
          xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
          mc:Ignorable="d" 
          d:DesignHeight="500" d:DesignWidth="750"
          ItemsSource="{Binding Alarms}"
          SelectedItem="{Binding SelectedAlarm, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
          SelectionChanged = "AlarmFramework_SelectionChanged"
          IsSynchronizedWithCurrentItem="True"
          CanUserResizeColumns="True" IsReadOnly="True" CanUserReorderColumns="False" CanUserSortColumns="False" SelectionMode="Single" CanUserAddRows="False"
          Background="White" RowHeaderWidth="0" AutoGenerateColumns="False" GridLinesVisibility="None" RowHeight="20" FrozenColumnCount = "1"
          ScrollViewer.CanContentScroll="False" ScrollViewer.VerticalScrollBarVisibility="Auto" ScrollViewer.HorizontalScrollBarVisibility="Auto"
          x:Name="AlarmFramework"
          behaviors:ElementActualSizeBehavior.ActualHeight="{Binding ListHeight}"

          >

        <i:Interaction.Triggers>
            <i:EventTrigger EventName="Loaded">
                <i:InvokeCommandAction Command="{Binding AlarmListLoadedCommand}" />
            </i:EventTrigger>
        </i:Interaction.Triggers>

    <DataGrid.Columns>

        <DataGridTemplateColumn Header="{x:Static Trans:TranslatedResources.AlarmColumnHeaderTime}" Width="auto" HeaderStyle="{StaticResource WithButt}">
            <DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal">
                        <components:FlagControl VerticalAlignment="Center" Height="15" Width="15" FlagColor="{Binding Severity, Converter={StaticResource AlarmSeverityToColorConverter}}"
                                                Visibility="{Binding AckStatus, Converter={StaticResource InvertedBoolToVisibilityConverter}, Mode=TwoWay}"/>
                        <TextBlock Text="{Binding DateTimeString}" Padding="10,0,0,0" HorizontalAlignment="Left" VerticalAlignment="Center"/>
                    </StackPanel>

                </DataTemplate>
            </DataGridTemplateColumn.CellTemplate>
        </DataGridTemplateColumn>

        <DataGridTextColumn Header="{x:Static Trans:TranslatedResources.AlarmColumnHeaderSeverity}" Binding="{Binding SeverityString}" Width="auto" HeaderStyle="{StaticResource WithoutButt}"/>

        <DataGridTextColumn Header="{x:Static Trans:TranslatedResources.AlarmColumnHeaderDescription}" Binding="{Binding Description}"  d:Width="400" Width="*" HeaderStyle="{StaticResource WithoutButt}"/>



    </DataGrid.Columns>
</DataGrid>

依賴屬性獲取實際高度

public class ElementActualSizeBehavior
{

    public static double GetActualWidth(DependencyObject obj)
    {
        return (double)obj.GetValue(ActualWidthProperty);
    }

    public static void SetActualWidth(DependencyObject obj, double value)
    {
        obj.SetValue(ActualWidthProperty, value);
    }

    public static double GetActualHeight(DependencyObject obj)
    {
        return (double)obj.GetValue(ActualHeightProperty);
    }

    public static void SetActualHeight(DependencyObject obj, double value)
    {
        obj.SetValue(ActualHeightProperty, value);
    }

    public static readonly DependencyProperty ActualWidthProperty = DependencyProperty.RegisterAttached("ActualWidth", typeof(double), typeof(ElementActualSizeBehavior), new FrameworkPropertyMetadata(double.NaN, new PropertyChangedCallback(ActualWidthChanged)) { BindsTwoWayByDefault = true });
    public static readonly DependencyProperty ActualHeightProperty = DependencyProperty.RegisterAttached("ActualHeight", typeof(double), typeof(ElementActualSizeBehavior), new FrameworkPropertyMetadata(double.NaN, new PropertyChangedCallback(ActualHeightChanged)) { BindsTwoWayByDefault = true });

    private static void ActualHeightChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
    {
        Control w = source as Control;
        if (w != null)
        {
            w.SizeChanged += (se, ev) =>
            {
                SetActualHeight((DependencyObject)se, ev.NewSize.Height);
            };
        }
    }

    private static void ActualWidthChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
    {
        Control w = source as Control;
        if (w != null)
        {
            w.SizeChanged += (se, ev) =>
            {
                SetActualWidth((DependencyObject)se, ev.NewSize.Width);
            };
        }
    }
}

視圖模型

public class AlarmListViewModel : MainViewModelBase
    {
    #region Properties

    private double _listHeight;
    public double ListHeight
    {
        get { return _listHeight; }
        set
        {
            if (Double.IsNaN(value))
            {
                //Debug.WriteLine("nan");
                return;
            }

            _listHeight = value;
            //Debug.WriteLine(value);
            RaisePropertyChanged(() => ListHeight);
        }
    }


    private ObservableCollection<AlarmEntryViewModel> _alarms;
    public ObservableCollection<AlarmEntryViewModel> Alarms
    {
        get { return _alarms; }
        set { Set(() => Alarms, ref _alarms, value); }
    }

    private AlarmEntryViewModel _selectedAlarm;
    public AlarmEntryViewModel SelectedAlarm
    {
        get { return _selectedAlarm; }
        set { Set(() => SelectedAlarm, ref _selectedAlarm, value); }
    }

    private int _acknowledgeAllowed;
    public int AcknowledgeAllowed
    {
        get { return _acknowledgeAllowed; }
        set { Set(() => AcknowledgeAllowed, ref _acknowledgeAllowed, value); }
    }

    private int _acknowledgableAlarms;
    public int AcknowledgableAlarms
    {
        get { return _acknowledgableAlarms; }
        set { Set(() => AcknowledgableAlarms, ref _acknowledgableAlarms, value); }
    }

    private int _rowHeight;
    public int RowHeight
    {
        get { return _rowHeight; }
        set { Set(() => RowHeight, ref _rowHeight, value); }
    }

    private readonly IActionCommand _acknowledgeCommand;
    public IActionCommand AcknowledgeCommand
    {
        get { return _acknowledgeCommand; }
    }

    private readonly IActionCommand _alarmListLoadedCommand;
    public IActionCommand AlarmListLoadedCommand
    {
        get { return _alarmListLoadedCommand; }
    }

    public int MaxAcknowledgedAlarm;
    public int AlarmToSendIndex { get; set; }

    #endregion

    #region Constructor

    public AlarmListViewModel()
    {
        //Lock collection to stop inconsistent item source exception
        Alarms = new ObservableCollection<AlarmEntryViewModel>();
        BindingOperations.EnableCollectionSynchronization(Alarms, _AlarmsLock);


        //Add command
        _acknowledgeCommand = new ActionCommand<AlarmEntryViewModel>(p => Acknowledge(p));
        _alarmListLoadedCommand = new ActionCommand<AlarmListViewModel>(p => Startup());
    }

    #endregion

    #region Private Methods



    private void Startup()
    {
        var rowsInView = (int)Math.Floor(ListHeight / RowHeight);
        var rowsInAlarms = Alarms.Count;
        var rowsNeeded = rowsInView - rowsInAlarms;
    }

Answer 1

最終有人向我解釋了問題並給出了解決方案。 問題在於用戶控件的高度/寬度在加載時實際上沒有改變。 它保持相對於其祖先的寬度/高度（或類似的東西）。 無論如何，這就是為什么您沒有在視圖模型中獲得更新的原因。

解決方案存在兩個部分。 首先，必須像上面的代碼中那樣實現ElementActionSizeBehavior。 然后，您必須明確聲明組件的大小。 這可以通過添加以下行來完成：

Height="{Binding RelativeSource={RelativeSource AncestorType={x:Type Control}}, Path=ActualHeight}"

因此，更新后的視圖標題應如下所示：

<DataGrid x:Class="Kwa.Presentation.Views.AlarmList.AlarmList"
          xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
          xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
          xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
          xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
          xmlns:local="clr-namespace:Kwa.Presentation.Views.AlarmList"
          xmlns:behaviors="clr-namespace:Kwa.Presentation.Behaviors"
          mc:Ignorable="d" 
          d:DesignHeight="500" d:DesignWidth="750"
          Height="{Binding RelativeSource={RelativeSource AncestorType={x:Type Control}}, Path=ActualHeight}"
behaviors:ElementActualSizeBehavior.ActualHeight="{Binding ListHeight}"
          >

您也不再需要交互部分。

希望這可以幫助其他人獲得他們的實際身高和寬度。