在加载时间获取实际高度

Question

我正在为数据网格制作用户控件。此数据网格有一些新的和新的条目。要求新条目显示在屏幕顶部，但数据顺序必须是按时间顺序排列的。因此，我通过添加空行将整个网格向上推动。例如，如果我有8个旧条目和2个新条目，则必须在两个新条目中的第一个上方"隐藏" 8个旧条目。

要计算空行，我想将用户控制的实际高度除以行高度。我找到了一种通过依赖项属性获得实际高度的方法（请参见下面的代码）。我一开始就需要它可用，因此我实现了一个触发器，以给我加载事件。但是此时，用户控件仍然具有0。

最后一个说明，我正在使用Galasoft MVVMLIGHT和匹配的MVVM模式。此外，依赖关系属性在首次初始化后更改窗口的高度时确实会给您正确的高度。

视图

<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>

依赖属性要获得实际的高度

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);
            };
        }
    }
}

视图模型

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

最终有人向我解释了问题并给出了解决方案。问题在于以下事实：用户控制的高度/宽度实际上不会在加载时间发生变化。它保持相对于祖先的宽度/高度（或类似的东西）。无论如何，这就是为什么您没有在查看模型中获得更新。

解决方案存在于两个部分。首先，必须像上面的代码中实现元素actizizebehavior。然后，您必须明确声明组件大小。这可以通过添加行来完成：

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

因此，更新的视图标头应该是这样的：

<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}"
          >

您也不再需要交互性零件。

希望这可以帮助他人以及获得实际的高度和宽度。