WPF - 如何将 WrapPanel 中的所有项目居中? [英] WPF - How can I center all items in a WrapPanel?

问题描述

我使用 WrapPanel 作为 ItemsControl 的 ItemsPanel.现在，控件中的项目如下所示:

I'm using a WrapPanel as the ItemsPanel of an ItemsControl. Right now, the items in the control wrap like this:

|1234567  |
|890      |

我希望它们像这样包装:

I'd like them to wrap like this:

| 1234567 |
|   890   |

从概念上讲，布局过程应该对齐每一行项目，使其在 WrapPanel 的边界内居中.

Conceptually, the layout process should align each line of items such that it's centered within the WrapPanel's bounds.

有人可以解释一下这是怎么可能的吗?

Can someone explain how this is possible please?

推荐答案

内置的 WrapPanel 将不允许您对齐其内容 - 只有它本身.这是一种允许您设置 Horizo​​ntalContentAlignment 的技术:

The built in WrapPanel will not allow you to align its content - only itself. Here is a technique that allows you to set HorizontalContentAlignment:

using System;
using System.Windows;
using System.Windows.Controls;

public class AlignableWrapPanel : Panel
{
    public HorizontalAlignment HorizontalContentAlignment
    {
        get { return (HorizontalAlignment)GetValue(HorizontalContentAlignmentProperty); }
        set { SetValue(HorizontalContentAlignmentProperty, value); }
    }

    public static readonly DependencyProperty HorizontalContentAlignmentProperty =
        DependencyProperty.Register("HorizontalContentAlignment", typeof(HorizontalAlignment), typeof(AlignableWrapPanel), new FrameworkPropertyMetadata(HorizontalAlignment.Left, FrameworkPropertyMetadataOptions.AffectsArrange));

    protected override Size MeasureOverride(Size constraint)
    {
        Size curLineSize = new Size();
        Size panelSize = new Size();

        UIElementCollection children = base.InternalChildren;

        for (int i = 0; i < children.Count; i++)
        {
            UIElement child = children[i] as UIElement;

            // Flow passes its own constraint to children
            child.Measure(constraint);
            Size sz = child.DesiredSize;

            if (curLineSize.Width + sz.Width > constraint.Width) //need to switch to another line
            {
                panelSize.Width = Math.Max(curLineSize.Width, panelSize.Width);
                panelSize.Height += curLineSize.Height;
                curLineSize = sz;

                if (sz.Width > constraint.Width) // if the element is wider then the constraint - give it a separate line                    
                {
                    panelSize.Width = Math.Max(sz.Width, panelSize.Width);
                    panelSize.Height += sz.Height;
                    curLineSize = new Size();
                }
            }
            else //continue to accumulate a line
            {
                curLineSize.Width += sz.Width;
                curLineSize.Height = Math.Max(sz.Height, curLineSize.Height);
            }
        }

        // the last line size, if any need to be added
        panelSize.Width = Math.Max(curLineSize.Width, panelSize.Width);
        panelSize.Height += curLineSize.Height;

        return panelSize;
    }

    protected override Size ArrangeOverride(Size arrangeBounds)
    {
        int firstInLine = 0;
        Size curLineSize = new Size();
        double accumulatedHeight = 0;
        UIElementCollection children = this.InternalChildren;

        for (int i = 0; i < children.Count; i++)
        {
            Size sz = children[i].DesiredSize;

            if (curLineSize.Width + sz.Width > arrangeBounds.Width) //need to switch to another line
            {
                ArrangeLine(accumulatedHeight, curLineSize, arrangeBounds.Width, firstInLine, i);

                accumulatedHeight += curLineSize.Height;
                curLineSize = sz;

                if (sz.Width > arrangeBounds.Width) //the element is wider then the constraint - give it a separate line                    
                {
                    ArrangeLine(accumulatedHeight, sz, arrangeBounds.Width, i, ++i);
                    accumulatedHeight += sz.Height;
                    curLineSize = new Size();
                }
                firstInLine = i;
            }
            else //continue to accumulate a line
            {
                curLineSize.Width += sz.Width;
                curLineSize.Height = Math.Max(sz.Height, curLineSize.Height);
            }
        }

        if (firstInLine < children.Count)
            ArrangeLine(accumulatedHeight, curLineSize, arrangeBounds.Width, firstInLine, children.Count);

        return arrangeBounds;
    }

    private void ArrangeLine(double y, Size lineSize, double boundsWidth, int start, int end)
    {
        double x = 0;
        if (this.HorizontalContentAlignment == HorizontalAlignment.Center)
        {
            x = (boundsWidth - lineSize.Width) / 2;
        }
        else if (this.HorizontalContentAlignment == HorizontalAlignment.Right)
        {
            x = (boundsWidth - lineSize.Width);
        }

        UIElementCollection children = InternalChildren;
        for (int i = start; i < end; i++)
        {
            UIElement child = children[i];
            child.Arrange(new Rect(x, y, child.DesiredSize.Width, lineSize.Height));
            x += child.DesiredSize.Width;
        }
    }
}

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