我正在为数据网格进行用户控制。此数据网格包含一些新旧条目。要求新条目显示在屏幕顶部，但数据顺序必须按时间顺序排列。所以我通过添加空行向上推动整个网格。例如，如果我有8个旧条目和2个新条目，那么8个旧条目必须是＆＃34;隐藏＆＃34;高于两个新条目中的第一个。
要计算空行，我想将用户控件的实际高度除以行高。我找到了一种通过依赖属性获取实际高度的方法（参见下面的代码）。我需要它在开始时可用，所以我实现了一个触发器，让我访问load事件。然而此时用户控件的大小仍为0.那么还有另一个事件可以让我在正确的时间计算出来吗？
最后一点，我正在使用Galasoft MVVMLight和匹配的mvvm模式。一旦你在第一次初始化后改变窗口的高度，依赖属性确实给出了正确的高度。
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>
获取实际高度的依赖属性
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;
}
答案 0 :(得分：0)
最终有人向我解释了这个问题并提出了解决方案。问题在于用户控件的高度/宽度在加载时实际上没有变化。它保持相对于它的祖先宽度/高度（或类似的东西）。无论如何，这就是你在视图模型中没有得到更新的原因。
解决方案分为两部分。首先，必须按照上面的代码实现ElementActionSizeBehavior。然后，您必须显式声明组件大小。这可以通过添加以下行来完成：
Height="{Binding RelativeSource={RelativeSource AncestorType={x:Type Control}}, Path=ActualHeight}"
因此更新的视图标题应该是这样的：
<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}"
>
您也不再需要交互部分了。
希望这可以帮助其他人获得他们的实际高度和宽度。