C# DataGridView：当列右对齐时，长文本在左侧被“...”截断

Question

我有一个关于单元格截断的问题（替换为“...”）：

当列右对齐时，如何在单元格左侧显示替换“...”？

我使用的是非等宽字体，所以我不能只计算字符来做一些字符串操作作为一种解决方法，我需要一个解决方案。我认为应该有。

为了说明我的问题，我在这里模拟我的 DataGridView

Left Context (Right aligned column)        | Center Word | Right Context (Left aligned column)
                left context not truncated | CenterWord  | Right context not truncated
...Here is the long left context truncated | CenterWord  | Here is the long right context truncated...

我想我已经说清楚了。

谢谢。请帮帮我。

彼得

P.S.：同样的问题可以在这个链接中找到： http://objectmix.com/csharp/341736-datagridview-cell-format-question.html

Answer 1

这绝对是一件不寻常的事情——但（就像其他任何事情一样）它是可以做到的。这是一个测量字符串大小并将其与单元格大小进行比较的问题。 （请注意，我假设数据是由用户输入的。如果您要进行数据绑定，则基本上必须使用其他事件。）

这可行，但可能需要一些微调：

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        dataGridView1.Columns.Add("col1", "col1");
        dataGridView1.Columns[0].CellTemplate.Style.Alignment = DataGridViewContentAlignment.MiddleRight;
        dataGridView1.Columns.Add("col2", "col2");
        dataGridView1.Columns.Add("col3", "col3");

        dataGridView1.Rows.Add();
        dataGridView1.CellEndEdit += new DataGridViewCellEventHandler(dataGridView1_CellEndEdit);
        dataGridView1.ColumnWidthChanged += new DataGridViewColumnEventHandler(dataGridView1_ColumnWidthChanged);              
    }

    void dataGridView1_ColumnWidthChanged(object sender, DataGridViewColumnEventArgs e)
    {
        if (e.Column.Index == 0)
        {
            // We need to truncate everything again when the width changes
            foreach (DataGridViewRow row in dataGridView1.Rows)
            {
                RightTruncateText(row.Cells[0]);
            }
        }
    }

    void RightTruncateText(DataGridViewCell cell)
    {                        
        // check if the content is too long:
        using (Graphics g = Graphics.FromHwnd(this.Handle))
        {
            SizeF size = g.MeasureString((string)cell.Tag, dataGridView1.Font); // NOTE: using the tag

            if (size.Width > cell.Size.Width)
            {
                StringBuilder truncated = new StringBuilder((string)cell.Tag);

                truncated.Insert(0, "...");

                // Truncate the string until small enough (NOTE: not optimized in any way!)                        
                while (size.Width > cell.Size.Width)
                {
                    truncated.Remove(3, 1);
                    size = g.MeasureString(truncated.ToString(), dataGridView1.Font);
                }
                cell.Value = truncated.ToString();
            }
            else
            {
                cell.Value = cell.Tag;
            }
        }
    }

    void dataGridView1_CellEndEdit(object sender, DataGridViewCellEventArgs e)
    {
        if (e.ColumnIndex == 0)
        {
            // Save the value in the tag but show the truncated value
            DataGridViewCell cell = dataGridView1.Rows[e.RowIndex].Cells[e.ColumnIndex];
            cell.Tag = cell.Value; // Saving the actual state
            RightTruncateText(cell);
        }
    }
}

Answer 2

我最终通过创建自己的DataGridViewLeftCropTextBoxCell 来实现这一点。不幸的是，DataGridViewTextBoxCell::Paint 是 bit a complicated method ^{Reference Source .NET Framework 4.5.2}，它使用了许多 .NET 内部方法。

但一开始我让基类绘制背景和边框（如果没有合理的前景，就离开它）。

然后测量文本并缩小它，直到它适合值范围。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Drawing;

namespace Project
{
    public class DataGridViewLeftCropTextBoxCell : DataGridViewTextBoxCell
    {

        /// <summary>
        /// Paints contents
        /// </summary>
        /// <param name="graphics"></param>
        /// <param name="clipBounds"></param>
        /// <param name="cellBounds"></param>
        /// <param name="rowIndex"></param>
        /// <param name="cellState"></param>
        /// <param name="value"></param>
        /// <param name="formattedValue"></param>
        /// <param name="errorText"></param>
        /// <param name="cellStyle"></param>
        /// <param name="advancedBorderStyle"></param>
        /// <param name="paintParts"></param>
        protected override void Paint( Graphics graphics, Rectangle clipBounds, Rectangle cellBounds, int rowIndex, DataGridViewElementStates cellState, object value, object formattedValue, string errorText, DataGridViewCellStyle cellStyle, DataGridViewAdvancedBorderStyle advancedBorderStyle, DataGridViewPaintParts paintParts )
        {
            string formattedString = formattedValue as string;

            // Nothing to draw
            if (String.IsNullOrEmpty( formattedString )) {
                base.Paint( graphics, clipBounds, cellBounds, rowIndex, cellState, value, formattedValue, errorText, cellStyle, advancedBorderStyle, paintParts );
                return;
            }

            // Draw parently without foreground
            base.Paint( graphics, clipBounds, cellBounds, rowIndex, cellState, value, formattedValue, errorText, cellStyle, advancedBorderStyle, paintParts & ~DataGridViewPaintParts.ContentForeground );

            // No foreground?
            if ((paintParts & DataGridViewPaintParts.ContentForeground) == DataGridViewPaintParts.None) {
                return;
            }

            // Calculate value bounds
            Rectangle borderWidths = BorderWidths( advancedBorderStyle );
            Rectangle valBounds = cellBounds;
            valBounds.Offset( borderWidths.X, borderWidths.Y );
            valBounds.Width -= borderWidths.Right;
            valBounds.Height -= borderWidths.Bottom;

            bool cellSelected = (cellState & DataGridViewElementStates.Selected) != 0;

            // Prepare text flags
            TextFormatFlags flags = ComputeTextFormatFlagsForCellStyleAlignment( this.DataGridView.RightToLeft == RightToLeft.Yes, cellStyle.Alignment, cellStyle.WrapMode );
            if ((flags & TextFormatFlags.SingleLine) != 0) {
                flags |= TextFormatFlags.EndEllipsis;
            }

            // Prepare size of text
            Size s = TextRenderer.MeasureText( graphics,
                formattedString,
                cellStyle.Font
            );

            // Text fits into bounds, just append
            if (s.Width < valBounds.Width) {
                TextRenderer.DrawText( graphics,
                    formattedString,
                    cellStyle.Font,
                    valBounds,
                    cellSelected ? cellStyle.SelectionForeColor : cellStyle.ForeColor,
                    flags );
                return;
            }

            // Prepare 
            StringBuilder truncated = new StringBuilder( formattedString );
            truncated.Insert( 0, "..." );

            // Truncate the string until it's small enough 
            while ((s.Width > valBounds.Width) && (truncated.Length > 5)) {
                truncated.Remove( 3, 1 );
                formattedString = truncated.ToString();
                s = TextRenderer.MeasureText( graphics,
                    formattedString,
                    cellStyle.Font
                );
            }

            TextRenderer.DrawText( graphics,
                formattedString,
                cellStyle.Font,
                valBounds,
                cellSelected ? cellStyle.SelectionForeColor : cellStyle.ForeColor,
                flags
            );
        }
    }
}

您还可以创建自己的列类型：

class DataGridViewLeftCropTextBoxColumn : DataGridViewTextBoxColumn
{
    public override DataGridViewCell CellTemplate
    {
        get { return new DataGridViewLeftCropTextBoxCell(); }
        set { base.CellTemplate = value; }
    }
}

---

我从steinar's answer 和TextFormatFlags ComputeTextFormatFlagsForCellStyleAlignment 借用了缩小的文字，从.NET Framework Reference Source。

Answer 3

我已经做了一个解决方法，除了“...”（截断效果很好）之外它都可以工作

    protected override void OnCellPainting(DataGridViewCellPaintingEventArgs e)
    {
        base.OnCellPainting(e);

        if (e.RowIndex >= 0 && e.ColumnIndex >= 0 &&
            CustomRightToLeftColumnNames.Contains(this.Columns[e.ColumnIndex].Name))
        {
            // Method 2:
            e.PaintBackground(e.CellBounds, true);

            if (e.FormattedValue != null)
            {
                TextFormatFlags flags = TextFormatFlags.RightToLeft         |
                                        TextFormatFlags.VerticalCenter      |
                                        TextFormatFlags.Right               |
                                        TextFormatFlags.LeftAndRightPadding;// |
                                        //TextFormatFlags.EndEllipsis;
                TextRenderer.DrawText
                (
                    e.Graphics,
                    e.FormattedValue.ToString(),
                    e.CellStyle.Font,
                    e.CellBounds,
                    e.CellStyle.ForeColor,
                    flags
                );
            }

            e.Handled = true;
        }
    }

此解决方案的唯一问题是我不知道如何设置 TextFormatFlags 以获得我想要的正确行为，与 DataGridView.RightToLeft = Yes 时完全相同。

如果我打开TextFormatFlags.EndEllipsis，三个点“...”会出现在左侧，但它会从字符串的右端截断。

我不确定要打开TextFormatFlags 枚举的哪个标志。