UWP打开时更改组合框位置 [英] UWP change ComboBox position when opening

问题描述

我在c＃XAML中有一个 ComboBox ，并且未选择任何内容并且显示了 PlaceHolderText 并单击

我希望下拉菜单在顶部打开。

假设我有一个 ComboBox 并用数字 1-100 填充，然后希望它从 1 开始显示强>。如果下拉列表中显示了七个项目，则数字 1-7 应该可见。正常行为是显示数字 47-53 。

旧的解决方法是使用 ListView ，但我不想要这个。

我该如何实现？

解决方案

该解决方法如何？

 使用Windows.UI.Xaml； 
使用Windows.UI.Xaml.Controls; 
 
命名空间StackOverFlowSampleApp 
 {
 public class ExtendedComboBox：ComboBox 
 {
 private ScrollViewer _scrollViewer; 
 
 public ExtendedComboBox（）
 {
 DefaultStyleKey = typeof（ComboBox）; 
} 
 
受保护的覆盖无效OnApplyTemplate（）
 {
 base.OnApplyTemplate（）; 
 _scrollViewer = GetTemplateChild（ ScrollViewer）作为ScrollViewer; 
 if（_scrollViewer！= null）
 {
 _scrollViewer.Loaded + = OnScrollViewerLoaded; 
} 
} 
 
私有无效OnScrollViewerLoaded（对象发送者，RoutedEventArgs e）
 {
 _scrollViewer.Loaded-= OnScrollViewerLoaded; 
 _scrollViewer.ChangeView（null，0，null）; 
} 
} 
} 
  

之前的工作方式：

解决方法后如何工作：

I have a ComboBox in c# XAML and when nothing is selected and the PlaceHolderText is shown and I click on it to open, the normal behavior is to open it in the middle.

I want the dropdown to open on top instead. Let's say I have a ComboBox and fill it with the number 1-100, then I want it to display beginning from 1. If there are seven items shown in the dropdown, then the numbers 1-7 should be visible. Normal behavior would be showing the numbers 47-53.

An old workaround would be using a ListView, but I don't want this.

How can I achieve this?

解决方案

What about this workaround?

using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;

namespace StackOverFlowSampleApp
{
    public class ExtendedComboBox : ComboBox
    {
        private ScrollViewer _scrollViewer;

        public ExtendedComboBox()
        {
            DefaultStyleKey = typeof(ComboBox);
        }

        protected override void OnApplyTemplate()
        {
            base.OnApplyTemplate();
            _scrollViewer = GetTemplateChild("ScrollViewer") as ScrollViewer;
            if (_scrollViewer != null)
            {
                _scrollViewer.Loaded += OnScrollViewerLoaded;
            }
        }

        private void OnScrollViewerLoaded(object sender, RoutedEventArgs e)
        {
            _scrollViewer.Loaded -= OnScrollViewerLoaded;
            _scrollViewer.ChangeView(null, 0, null);
        }
    }
}

How it works before:

How it works after workaround:

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