Question

Visual Studio抱怨：警告1设计人员必须创建“RentalEase.CustomBindingNavForm”类型的实例，但它不能，因为该类型被声明为抽象。

Visual Studio不允许我访问表单的Designer。该类已经实现了CustomBindingNavForm中的所有抽象方法。 CustomBindingNavForm提供了一些具体和抽象的函数。

有解决方法吗？

这是班级：

 public abstract class CustomBindingNavForm : SingleInstanceForm {     

        //Flags for managing BindingSource
        protected bool isNew = false;
        protected bool isUpdating = false;

        /// <summary>
        /// This is so that when a new item is added, it sets isNew and firstPass to true. The Position Changed Event will look for
        /// firstPass and if it is true set it to false. Then on the next pass, it will see it's false and set isNew to false.
        /// This is needed because the Position Changed Event will fire when a new item is added.
        /// </summary>
        protected bool firstPass = false;


        protected abstract bool validateInput();
        protected abstract void saveToDatabase();


        //manipulating binding
        protected abstract void bindingSourceCancelResetCurrent();
        protected abstract void bindingSourceRemoveCurrent();
        protected abstract void bindingSourceMoveFirst();
        protected abstract void bindingSourceMoveNext();
        protected abstract void bindingSourceMoveLast();
        protected abstract void bindingSourceMovePrevious();
        protected abstract void bindingSourceAddNew();

        public void bindingNavigatorMovePreviousItem_Click(object sender, EventArgs e) {
            if (validateInput()) {
                bindingSourceMovePrevious();
            } else {
                DialogResult cont = MessageBox.Show(null, "There are errors in your data. Click Cancel to go back and fix them, or ok to continue. If you continue, changes will not be saved.", "Continue?", MessageBoxButtons.OKCancel, MessageBoxIcon.Question, MessageBoxDefaultButton.Button2);
                if (cont == DialogResult.OK) {
                    if (isNew) {
                        bindingSourceRemoveCurrent();
                        isNew = false;
                    } else {
                        bindingSourceCancelResetCurrent();
                        bindingSourceMovePrevious();
                    }
                }
            }
        }

        public void bindingNavigatorAddNewItem_Click(object sender, EventArgs e) {
            if (validateInput()) {
                saveToDatabase();
                bool temp = isUpdating;
                isUpdating = true;
                bindingSourceAddNew();
                isUpdating = temp;

                isNew = true;
                firstPass = true;
            } else {
                DialogResult cont = MessageBox.Show(null, "There are errors in your data. Click Cancel to go back and fix them, or ok to continue. If you continue, changes will not be saved.", "Continue?", MessageBoxButtons.OKCancel, MessageBoxIcon.Question, MessageBoxDefaultButton.Button2);
                if (cont == DialogResult.OK) {

                    if (isNew) {
                        bindingSourceRemoveCurrent();
                        isNew = false;
                    } else {
                        bindingSourceCancelResetCurrent();
                    }

                    bool temp = isUpdating;
                    isUpdating = true;
                    bindingSourceAddNew();
                    isUpdating = temp;

                    isNew = true;
                    firstPass = true;
                }
            }
        }

        public void bindingNavigatorMoveFirstItem_Click(object sender, EventArgs e) {
            if (validateInput()) {
                bindingSourceMoveFirst();
            } else {
                DialogResult cont = MessageBox.Show(null, "There are errors in your data. Click Cancel to go back and fix them, or ok to continue. If you continue, changes will not be saved.", "Continue?", MessageBoxButtons.OKCancel, MessageBoxIcon.Question, MessageBoxDefaultButton.Button2);
                if (cont == DialogResult.OK) {
                    if (isNew) {
                        bindingSourceRemoveCurrent();
                        isNew = false;
                    } else {
                        bindingSourceCancelResetCurrent();
                    }
                    bindingSourceMoveFirst();
                }
            }
        }

        public void bindingNavigatorMoveNextItem_Click(object sender, EventArgs e) {
            if (validateInput()) {
                bindingSourceMoveNext();
            } else {
                DialogResult cont = MessageBox.Show(null, "There are errors in your data. Click Cancel to go back and fix them, or ok to continue. If you continue, changes will not be saved.", "Continue?", MessageBoxButtons.OKCancel, MessageBoxIcon.Question, MessageBoxDefaultButton.Button2);
                if (cont == DialogResult.OK) {
                    if (isNew) {
                        bindingSourceRemoveCurrent();
                        isNew = false;
                    } else {
                        bindingSourceCancelResetCurrent();
                    }
                    bindingSourceMoveNext();
                }
            }
        }
    }

Answer 1

我还没有看到城市马铃薯（它的下来）的内容，但我和Smelch提出了一个解决方案。 Form本身继承自一个抽象类，所以他们没有告诉你的是它唯一的第一层继承不能抽象，第二层就可以了。

从那里，它只是在中间有一个空类，并在表单声明周围包裹#if debug，你很高兴。只需确保在发布模式下发布并在调试模式下进行设计（这是非常典型的）。

在设计（调试）和构建（发布）时，您将获得完整的设计器支持和真正的抽象基类，因为每次它最终都使用您的抽象基类。

The full explanation and answer is here

Answer 2

您可以使用抽象类上的属性来解决此问题，如下所示：

[TypeDescriptionProvider(typeof(AbstractControlDescriptionProvider<MyBaseFormEf, Form>))]

这将在您需要的每种情况下起作用。下面是AbstractControlDescriptionProvider

public class AbstractControlDescriptionProvider<TAbstract, TBase> : TypeDescriptionProvider
{
    public AbstractControlDescriptionProvider()
        : base(TypeDescriptor.GetProvider(typeof(TAbstract)))
    {
    }

    public override Type GetReflectionType(Type objectType, object instance)
    {
        if (objectType == typeof(TAbstract))
            return typeof(TBase);

        return base.GetReflectionType(objectType, instance);
    }

    public override object CreateInstance(IServiceProvider provider, Type objectType, Type[] argTypes, object[] args)
    {
        if (objectType == typeof(TAbstract))
            objectType = typeof(TBase);

        return base.CreateInstance(provider, objectType, argTypes, args);
    }
}

Answer 3

这对我有用，它继承了UserControl的抽象类

public class AbstractCommunicatorProvider : TypeDescriptionProvider
{
    public AbstractCommunicatorProvider(): base(TypeDescriptor.GetProvider(typeof(UserControl)))
    {
    }
    public override Type GetReflectionType(Type objectType, object instance)
    {
        return typeof(UserControl);
    }
    public override object CreateInstance(IServiceProvider provider, Type objectType, Type[] argTypes, object[] args)
    {
        objectType = typeof(UserControl);
        return base.CreateInstance(provider, objectType, argTypes, args);
    }
}


[TypeDescriptionProvider(typeof(AbstractCommunicatorProvider))]
public abstract partial class SelectorBase : UserControl
{

///class contents 
}

我不需要将其添加到所有派生类中，但是在您的情况下，您可能需要这样做。

设计者必须创建一个......的实例，因为该类型被声明为abstract

3 个答案: