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我终于找到了一个我整个周末都在努力解决的错误，但是我看不到真正解决它的方法 - 就是以一种干净的方式。

情况是我有一个绑定到业务对象列表的 DGV 控件。其中一列未绑定到 DataSource，我已经连接了 CellParsing 和 CellFormatting 事件来处理此单元格的数据的持久性。我基本上绕过了 .net 数据绑定并实现了我自己的糟糕版本。这不是故意的，它是真正的旧代码，具有复杂的解析和格式化要求，我错误地实现了基于未绑定列的解决方案。我现在知道处理这个问题的正确方法，并且已经修复了我的代码，但是我仍然想知道如何以另一种方式解决这个错误。

我处理 RowValidating 事件并对整个行进行最终验证，以确保一切正常。当然，如果出现问题，我会取消验证并且未提交该行。当用户通过 UI 交互编辑和添加行时，这一切都可以正常工作，但在设置 DataSource 时会产生问题。问题似乎是当 DGV 更新其内部列表并构建行时未调用 CellFormatting，或者至少在触发验证事件之前未调用它。这会导致 RowValidating 处理程序从 Unbound 列中提取一个空值（因为尚未调用 CellFormatting 并设置该值）。

我正在刷新我对 DGV 的了解，并认为处理 CellValueNeeded 事件可能是票，但设置 DataGridViewCellValueEventArgs.Value 并没有像我希望的那样触发 CellFormatting 事件。

我一直在考虑如何处理这种情况，我想出的唯一方法是检测何时从 UI 事件触发验证，而不是初始绑定或绑定列表更改。这不仅是一个 hacky 解决方案，而且看不到它是如何完成的。

我创建了一个完整的示例应用程序来说明问题。我真的很想知道你们中的一些人将如何解决这样的问题。这里很可能有主要的设计气味。

using System;
using System.Collections.Generic;
using System.Windows.Forms;

public class Form1 : Form
{
    private List<DomainModel> _sampleData;
    public Form1()
    {
        InitializeComponent();

        _sampleData = new List<DomainModel>();
        _sampleData.Add(new DomainModel("Widget A"));
        _sampleData.Add(new DomainModel("Widget B"));
    }

    private void button1_Click(object sender, EventArgs e)
    {
        Console.WriteLine("Setting DataSource");
        domainModelBindingSource.DataSource = _sampleData;
    }

    private void dataGridView1_CellFormatting(object sender,
        DataGridViewCellFormattingEventArgs e)
    {
        Console.WriteLine("CellFormatting fired for {0},{1}",
            e.RowIndex, e.ColumnIndex);

        if (e.ColumnIndex != 0 && !dataGridView1.Rows[e.RowIndex].IsNewRow)
        {
            var model = domainModelBindingSource[e.RowIndex] as DomainModel;
            e.Value = model.Name;
            e.FormattingApplied = true;
        }
    }

    private void dataGridView1_CellParsing(object sender, DataGridViewCellParsingEventArgs e)
    {
        if (e.ColumnIndex == 1)
        {
            e.Value = e.Value.ToString();
            e.ParsingApplied = true;
        }
    }

    private void dataGridView1_RowValidating(object sender, DataGridViewCellCancelEventArgs e)
    {
        if (dataGridView1.Rows[e.RowIndex].IsNewRow)
            return;

        object value = dataGridView1[1, e.RowIndex].Value;
        if (value == null || String.IsNullOrEmpty(value.ToString()))
            e.Cancel = true;
    }

    #region Designer stuff

    private System.ComponentModel.IContainer components = null;
    protected override void Dispose(bool disposing)
    {
        if (disposing && (components != null))
            components.Dispose();

        base.Dispose(disposing);
    }

    #region Windows Form Designer generated code

    private void InitializeComponent()
    {
            this.components = new System.ComponentModel.Container();
            this.dataGridView1 = new System.Windows.Forms.DataGridView();
            this.nameDataGridViewTextBoxColumn = new System.Windows.Forms.DataGridViewTextBoxColumn();
            this.Column1 = new System.Windows.Forms.DataGridViewTextBoxColumn();
            this.domainModelBindingSource = new System.Windows.Forms.BindingSource(this.components);
            this.button1 = new System.Windows.Forms.Button();
            ((System.ComponentModel.ISupportInitialize)(this.dataGridView1)).BeginInit();
            ((System.ComponentModel.ISupportInitialize)(this.domainModelBindingSource)).BeginInit();
            this.SuspendLayout();
            // 
            // dataGridView1
            // 
            this.dataGridView1.Anchor = ((System.Windows.Forms.AnchorStyles)((((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Bottom) 
            | System.Windows.Forms.AnchorStyles.Left) 
            | System.Windows.Forms.AnchorStyles.Right)));
            this.dataGridView1.AutoGenerateColumns = false;
            this.dataGridView1.ColumnHeadersHeightSizeMode = System.Windows.Forms.DataGridViewColumnHeadersHeightSizeMode.AutoSize;
            this.dataGridView1.Columns.AddRange(new System.Windows.Forms.DataGridViewColumn[] {
            this.nameDataGridViewTextBoxColumn,
            this.Column1});
            this.dataGridView1.DataSource = this.domainModelBindingSource;
            this.dataGridView1.Location = new System.Drawing.Point(12, 41);
            this.dataGridView1.Name = "dataGridView1";
            this.dataGridView1.Size = new System.Drawing.Size(437, 161);
            this.dataGridView1.TabIndex = 0;
            this.dataGridView1.CellFormatting += new System.Windows.Forms.DataGridViewCellFormattingEventHandler(this.dataGridView1_CellFormatting);
            this.dataGridView1.CellParsing += new System.Windows.Forms.DataGridViewCellParsingEventHandler(this.dataGridView1_CellParsing);
            this.dataGridView1.RowValidating += new System.Windows.Forms.DataGridViewCellCancelEventHandler(this.dataGridView1_RowValidating);
            // 
            // nameDataGridViewTextBoxColumn
            // 
            this.nameDataGridViewTextBoxColumn.DataPropertyName = "Name";
            this.nameDataGridViewTextBoxColumn.HeaderText = "Name";
            this.nameDataGridViewTextBoxColumn.Name = "nameDataGridViewTextBoxColumn";
            // 
            // Column1
            // 
            this.Column1.HeaderText = "Data (unbound)";
            this.Column1.Name = "Column1";
            // 
            // domainModelBindingSource
            // 
            this.domainModelBindingSource.DataSource = typeof(DomainModel);
            // 
            // button1
            // 
            this.button1.Location = new System.Drawing.Point(12, 12);
            this.button1.Name = "button1";
            this.button1.Size = new System.Drawing.Size(168, 23);
            this.button1.TabIndex = 1;
            this.button1.Text = "Update Data Source";
            this.button1.UseVisualStyleBackColor = true;
            this.button1.Click += new System.EventHandler(this.button1_Click);
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(461, 214);
            this.Controls.Add(this.button1);
            this.Controls.Add(this.dataGridView1);
            this.Name = "Form1";
            this.Text = "Form1";
            ((System.ComponentModel.ISupportInitialize)(this.dataGridView1)).EndInit();
            ((System.ComponentModel.ISupportInitialize)(this.domainModelBindingSource)).EndInit();
            this.ResumeLayout(false);
    }

    #endregion

    private System.Windows.Forms.DataGridView dataGridView1;
    private System.Windows.Forms.BindingSource domainModelBindingSource;
    private System.Windows.Forms.Button button1;
    private System.Windows.Forms.DataGridViewTextBoxColumn nameDataGridViewTextBoxColumn;
    private System.Windows.Forms.DataGridViewTextBoxColumn Column1;

    #endregion
}

internal sealed class DomainModel
{
    public DomainModel() { }

    public DomainModel(string name)
    {
        this.Name = name;
    }

    public string Name { get; set; }
}

static class Program
{
    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new Form1());
    }
}
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1 回答 1

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I had mentioned that I already "fixed the problem" which wasn't completely accurate. I fixed it in the test application, effectively validating the solution I was planning on using, but hadn't actually implemented it. Once I tried to I realized why I did things the way I did originally: The data that is used in the unbound column is a read-only collection of objects and in order to set them I need to call a separate method on the object. Best practices and all...

Well, read only properties of course can't be edited in the DGV so I was dead in the water. This made me go BACK to my original design and while researching I stumbled on this column/blog by Brian Noyes.

He mentions the event RowsAdded and that's all I needed! Here is the solution for my problem:

private void dataGridView1_RowsAdded(object sender, 
    DataGridViewRowsAddedEventArgs e)
{
    if (dataGridView1.Rows[e.RowIndex].IsNewRow)
    {
        return;
    }

    dataGridView1[1, e.RowIndex].Value = 
        (dataGridView1.Rows[e.RowIndex].DataBoundItem as DomainModel).Name;
}

I like this solution because it's placing the data on the Cell the same way it would if it were bound, it then hands off formatting responsibility to CellFormatting and I can do my work. Likewise I can parse the data and construct the required objects to pass to my bound objects "SetListData" method.

All good!

于 2012-04-23T07:23:35.823 回答