c# - 添加第二个 DatagridViewRow 导致克隆

Question

我遇到了一个有趣的问题。当我只将一个 DataGridViewRow 添加到 DataGridView 时，一切都按预期工作:DataGridView.Rows[0] 是添加的行。当我以某种方式添加第二个 DataGridviewRow 时，不再添加实际的 DataGridViewRows，而是添加克隆。看起来完全相同但实际上不是同一对象的克隆。

所以我想知道这是为什么，这种行为从何而来，如果可能的话如何阻止添加克隆而不是实际行。我查看了带有 Reflector 的 DataGridViewRowCollection 的代码，但找不到任何可疑的东西 - 但也许我错过了一些东西。

这是一个复制问题的代码示例:

DataGridView dgv = new DataGridView { AllowUserToAddRows = false };

DataGridViewTextBoxColumn dgColumn = new DataGridViewTextBoxColumn();
dgv.Columns.Add(dgColumn);

DataGridViewRow drFirst = new DataGridViewRow();
dgv.Rows.Add(drFirst); // Comment this line to showcase the problem

DataGridViewRow drSecond = new DataGridViewRow();
drSecond.Tag = new object();
dgv.Rows.Add(drSecond);

// When drFirst is added this is false - when it isn't this is true (as it should always be?)
bool thisSeemsWrong = object.ReferenceEquals(dgv.Rows[dgv.Rows.Count - 1], drSecond);

// Always true
bool thisSeemsRight = object.ReferenceEquals(dgv.Rows[dgv.Rows.Count - 1].Tag, drSecond.Tag);

Answer 1

Item DataGridViewRowCollection 类的属性创建 GridViewRow 的克隆并返回它，因此 ReferenceEquals 应该始终为 false不止一排。

DataGridViewRow row2 = (DataGridViewRow) dataGridViewRow.Clone();

但如果只有一行且index=0，则返回相同的引用。

if (((index == 0) && (this.items.Count() == 1))) {
      dataGridViewRow.IndexInternal = 0;
      dataGridViewRow.StateInternal = this.SharedRowState[0];
      if (((this.DataGridView != null))) {
          this.DataGridView.OnRowUnshared(dataGridViewRow);
      }
      return dataGridViewRow;
}

这是此属性的完整来源(来自 Reflection):

public DataGridViewRow this[int index]
{
  get
  {
    DataGridViewRow dataGridViewRow = this.SharedRow(index);
    if (dataGridViewRow.Index != -1)
    {
      return dataGridViewRow;
    }
    if ((index == 0) && (this.items.Count == 1))
    {
      dataGridViewRow.IndexInternal = 0;
      dataGridViewRow.StateInternal = this.SharedRowState(0);
      if (this.DataGridView != null)
      {
        this.DataGridView.OnRowUnshared(dataGridViewRow);
      }
      return dataGridViewRow;
    }
    DataGridViewRow row2 = (DataGridViewRow) dataGridViewRow.Clone();
    row2.IndexInternal = index;
    row2.DataGridViewInternal = dataGridViewRow.DataGridView;
    row2.StateInternal = this.SharedRowState(index);
    this.SharedList[index] = row2;
    int num = 0;
    foreach (DataGridViewCell cell in row2.Cells)
    {
      cell.DataGridViewInternal = dataGridViewRow.DataGridView;
      cell.OwningRowInternal = row2;
      cell.OwningColumnInternal = this.DataGridView.Columns[num];
      num++;
    }
    if (row2.HasHeaderCell)
    {
      row2.HeaderCell.DataGridViewInternal = dataGridViewRow.DataGridView;
      row2.HeaderCell.OwningRowInternal = row2;
    }
    if (this.DataGridView != null)
    {
      this.DataGridView.OnRowUnshared(row2);
    }
    return row2;
  }
}

也许您会在以下文章(从“使用共享行”开始)中找到有关原因的信息:

http://msdn.microsoft.com/en-us/library/ha5xt0d9.aspx