未选中 DateTimePicker 时（在开始时）未将 DateTime 值分配给 DateTimePicker

Question

在 WinForms 应用程序中，我有一个 DateTimePicker

来自...Designer.cs的属性

        this.dateTimePicker.AllowDrop = true;
        this.dateTimePicker.CustomFormat = "HH:mm:ss";
        this.dateTimePicker.Format = System.Windows.Forms.DateTimePickerFormat.Custom;
        this.dateTimePicker.Location = new System.Drawing.Point(251, 12);
        this.dateTimePicker.Name = "DateTimePicker";
        this.dateTimePicker.ShowCheckBox = true;
        this.dateTimePicker.ShowUpDown = true;
        this.dateTimePicker.Size = new System.Drawing.Size(200, 28);
        this.dateTimePicker.TabIndex = 1;

每当它的值发生变化时，我都会将我需要的内容保存到应用程序设置中（我对许多其他“字段”做了类似的事情，这是我遇到问题的第一个问题：

... this.Settings = [MyApplication].Properties.Settigns.Default.

private void dateTimePicker1_ValueChanged(object sender, EventArgs e)
{
    this.Settings.dateTimePicker_Time = this.dateTimePicker.Value;
    this.Settings.dateTimePicker_Checked = this.dateTimePicker.Checked;
    this.Settings.Save();
}

应用程序启动时，实际上在主窗体的构造函数中，我将保存的值恢复如下，（注意ValueChange事件仅在分配初始值后才绑定到控件）：

        this.dateTimePicker_Time.Checked = this.Settings.dateTimePicker_Checked;
        if (this.Settings.dateTimePicker_Time != null)
        {
            this.dateTimePicker.Value = this.Settings.dateTimePicker_Time;
        }

        this.dateTimePicker.ValueChanged += new System.EventHandler(this.dateTimePicker_ValueChanged);

问题 如果选中 DateTimePicker，则按预期分配 DateTime 值。 但是如果DateTimePicker没有勾选，DateTime的值没有赋值，好像DateTime.Now被赋值了。

因此，我也尝试了以下代码，但结果是一样的：

        this.dateTimePicker_Time.Checked = this.Settings.dateTimePicker_Checked;
        if (this.Settings.dateTimePicker_Time != null)
        {
            bool dateTimePicker_Checked = this.dateTimePicker.Checked;
            this.dateTimePicker.Checked = true;
            this.dateTimePicker.Value = this.Settings.dateTimePicker_Time;
            this.dateTimePicker.Checked = dateTimePicker_Checked ;
        }

        this.dateTimePicker.ValueChanged += new System.EventHandler(this.dateTimePicker_ValueChanged);

编辑 我尝试将 DateTimePicker 属性数据绑定到应用程序设置，但结果与上面“手动”执行的操作相同。

Answer 1

当您在构造函数中时，控件的某些设置尚未准备好。您找到了其中一项设置。

尝试将您的恢复代码移至表单的 OnLoad 覆盖。请注意，更改 DateTimePicker 的 Value 属性会将 Checked 属性设置为 true，因此您需要在设置 Value 属性之后设置 Checked 属性：

protected override void OnLoad(EventArgs e) {
  base.OnLoad(e);
  if (this.Settings.dateTimePicker_Time != null) {
    this.dateTimePicker2.Value = this.Settings.dateTimePicker_Time;
  }
  this.dateTimePicker2.Checked = this.Settings.dateTimePicker_Checked;
}

此外，在 OnFormClosing 覆盖中只保存一次设置会更有意义：

protected override void OnFormClosing(FormClosingEventArgs e) {
  this.Settings.dateTimePicker_Time = dateTimePicker2.Value;
  this.Settings.dateTimePicker_Checked = dateTimePicker2.Checked;
  this.Settings.Save();
  base.OnFormClosing(e);
}