Question

我正在制作一个在Windows窗体应用程序中使用的扩展方法库。我打算创建的方法之一将使输入控件上的错误状态更容易设置，例如

public static void SetError(this System.Windows.Forms.TextBox textBox, string errorMessage)
{
    if (string.IsNullOrEmpty(errorMessage))
    {
        //reset control state
        textBox.BackColor = System.Drawing.SystemColors.WindowText;
    }
    else
    {
        //set background colour to a nice shade of red
        textBox.BackColor = System.Drawing.Color.MistyRose;
    }

    //try to locate an ErrorProvider on the control's containing form.
    var errorProvider = LocateErrorProvider(textBox);

    if (errorProvider != null)
    {
        //set error message on error provider (or clear it)
        errorProvider.SetError(textBox, errorMessage);
    }
}

我想找出LocateErrorProvider方法。我想要做的是检查我的表单上是否存在ErrorProvider，如果它存在则只使用它。

ErrorProvider是Component而不是Control，因此我无法通过form.Controls属性访问它。我已经尝试将父表单转换为各种对象，但无济于事。

UPDATE ：我已设法使用以下代码使用反射来访问ErrorProvider：

private static System.Windows.Forms.ErrorProvider GetErrorProvider(System.Windows.Forms.Control control)
{
    //get the containing form of the control
    var form = control.GetContainerControl();

    //use reflection to get to "components" field
    var componentField = form.GetType().GetField("components", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);

    if (componentField != null)
    {
        //get the component collection from field
        var components = componentField.GetValue(form);

        //locate the ErrorProvider within the collection
        return (components as System.ComponentModel.IContainer).Components.OfType<System.Windows.Forms.ErrorProvider>().FirstOrDefault();
    }
    else
    {
        return null;
    }
}

就个人而言，我不太喜欢使用硬编码的字段名称来到现场。但在这种情况下它似乎工作得很好。有没有人有更好的方法来获得相同的结果？

Answer 1

到目前为止，这似乎解决了我的问题：

private static System.Windows.Forms.ErrorProvider GetErrorProvider(System.Windows.Forms.Control control)
{
    //get the containing form of the control
    var form = control.GetContainerControl();

    //use reflection to get to "components" field
    var componentField = form.GetType().GetField("components", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);

    if (componentField != null)
    {
        //get the component collection from field
        var components = componentField.GetValue(form);

        //locate the ErrorProvider within the collection
        return (components as System.ComponentModel.IContainer).Components.OfType<System.Windows.Forms.ErrorProvider>().FirstOrDefault();
    }
    else
    {
        return null;
    }
}

感谢Hans＆amp;科迪的出色创意。

Answer 2

这就是设计接口的目的。他们强制执行一个类来实现行为。您需要的行为是表单具有ErrorProvider。所以写一个这样的界面：

public interface IHasErrorProvider {
    ErrorProvider Provider { get; }
}

让表单与错误提供程序实现接口：

public partial class Form1 : Form, IHasErrorProvider {
    public ErrorProvider Provider {
        get { return errorProvider1; }
    }
    // etc..
}

现在检索错误提供程序很简单：

    private static ErrorProvider GetErrorProvider(Control control) {
        var impl = control.FindForm() as IHasErrorProvider;
        return impl != null ? impl.Provider : null;
    }

Answer 3

在VS2005中

可行：

    private static System.Windows.Forms.ErrorProvider GetErrorProvider(System.Windows.Forms.Control control)
    {
        try
        {
            //get the containing form of the control
            System.Windows.Forms.IContainerControl form = control.GetContainerControl();

            //use reflection to get to "components" field
            System.Reflection.FieldInfo componentField = form.GetType().GetField("components", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);

            if (componentField != null)
            {
                //get the component collection from field
                object components = componentField.GetValue(form);
                object oReturn = null;
                //locate the ErrorProvider within the collection
                foreach (object o in ((System.ComponentModel.Container)components).Components)
                {
                    if (o.GetType() == typeof(System.Windows.Forms.ErrorProvider))
                    {
                        oReturn = o;
                        break;
                    }
                }
                return (ErrorProvider)oReturn;
            }
        }
        catch 
        {
            return null;
        }
        return null;
    }

在运行时在Windows窗体上找到ErrorProvider

3 个答案: