WPF DataGrid：高效获取单元格所在行索引的方法

Nice find! You’re right that most common solutions for grabbing a row index from DataGridCellInfo rely on slow linear searches (like Items.IndexOf(cellInfo.Item)), which get painful with large datasets. Leveraging the internal ItemInfo property is a smart way to skip that overhead—here’s how to implement it properly:

How It Works #

The DataGridCellInfo internally stores an ItemInfo object that tracks the exact index of the row it belongs to. Since this is a non-public property, we’ll use reflection to access it, letting us pull the index in O(1) time instead of the O(n) cost of linear searches.

Step-by-Step Implementation #

Create an extension method to make this reusable across your project:

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

public static class DataGridCellInfoExtensions
{
    public static int GetRowIndex(this DataGridCellInfo cellInfo)
    {
        // Guard against invalid cell info
        if (!cellInfo.IsValid)
            throw new ArgumentException("The provided DataGridCellInfo is invalid.", nameof(cellInfo));

        // Retrieve the non-public ItemInfo property
        var itemInfoProperty = typeof(DataGridCellInfo).GetProperty(
            "ItemInfo", 
            BindingFlags.NonPublic | BindingFlags.Instance);
        
        if (itemInfoProperty == null)
            throw new InvalidOperationException("Could not access the internal ItemInfo property. This may be due to a WPF version change.");

        var itemInfo = itemInfoProperty.GetValue(cellInfo);
        if (itemInfo == null)
            return -1;

        // Get the Index field from the ItemInfo object
        var indexField = itemInfo.GetType().GetField(
            "Index", 
            BindingFlags.Public | BindingFlags.Instance);
        
        if (indexField == null)
            throw new InvalidOperationException("Could not access the Index field in ItemInfo. This may be due to a WPF version change.");

        return (int)indexField.GetValue(itemInfo);
    }
}

Usage Example #

Just call the extension method on any valid DataGridCellInfo:

DataGridCellInfo selectedCell = myDataGrid.SelectedCells[0];
int rowIndex = selectedCell.GetRowIndex();

Important Caveats #

Since we’re tapping into internal WPF APIs:

• Version Compatibility: Microsoft might rename, modify, or remove ItemInfo or the Index field in future .NET/WPF updates. Always test this code when upgrading your framework version.
• Fallback Plan: For robustness, add a fallback to the linear search method if reflection fails. Here’s how to extend the method:

public static int GetRowIndexSafe(this DataGridCellInfo cellInfo, DataGrid dataGrid)
{
    try
    {
        return cellInfo.GetRowIndex();
    }
    catch (Exception)
    {
        // Fall back to the standard (slower) method if reflection fails
        return dataGrid?.Items.IndexOf(cellInfo.Item) ?? -1;
    }
}

Why This Is Better #

• Performance: Directly accessing the stored index avoids iterating through the entire Items collection, which is a massive win for large DataGrids with hundreds or thousands of rows.
• Accuracy: Unlike visual tree traversal workarounds, this uses the same index the DataGrid internally tracks, so it’s less prone to errors from virtualization or UI state changes.

内容的提问来源于stack exchange，提问作者melmi