Question

This probably applies to other places, but in WinForms, when I use binding I find many methods want to take the name of the property to bind to. Something like:

class Person
{
    public String Name { get { ... } set { ... } }
    public int Age { get { ... } set { ... } }
}

class PersonView
{
    void Bind(Person p)
    {
        nameControl.Bind(p,"Name");
        ageControl.Bind(p,"Age");
    }
}

The big problem I keep having with this is that “Name” and “Age” are specified as strings. This means the compiler is no help if someone renames one of Person’s properties. The code will compile fine, but the bindings will be broken.

Is there a standard way of solving this that I’ve missed? It feels like I need some keyword, maybe called stringof to match the existing typeof. You could use it something like:

ageControl.Bind(p,stringof(p.Age).Name);

stringof could return some class that has properties for getting the full path, part of the path, or the string so you can parse it up yourself.

Is something like this already do-able?

Answer 1

You can use Expressions to get compiler-checked bindings.
For example, in one of current projects we set up bindings like this:

DataBinder
    .BindToObject(this)
    .ObjectProperty(c => c.IsReadOnly)
        .Control(nameTextBox, n => n.ReadOnly)
        .Control(addressControl, n => n.ReadOnly)

Code supporting this style is separated into several classes:

public static class DataBinder
{
    public static DataBinderBindingSourceContext<TDataSource> BindToObject<TDataSource>(TDataSource dataSource)
    {
        return new DataBinderBindingSourceContext<TDataSource>(dataSource);
    }
}

public class DataBinderBindingSourceContext<TDataSource> 
{
    public readonly object DataSource;

    public DataBinderBindingSourceContext(object dataSource)
    {
        DataSource = dataSource;
    }

    public DataBinderControlContext<TDataSource, TProperty> ObjectProperty<TProperty>(Expression<Func<TDataSource, TProperty>> property)
    {
        return new DataBinderControlContext<TDataSource, TProperty>(this, property);
    }
}

public class DataBinderControlContext<TDataSource, TProperty>
{
    readonly DataBinderBindingSourceContext<TDataSource> BindingSourceContext;
    readonly string ObjectProperty;

    public DataBinderControlContext
        (
            DataBinderBindingSourceContext<TDataSource> bindingSourceContext,
            Expression<Func<TDataSource, TProperty>> objectProperty
        )
    {
        BindingSourceContext = RequireArg.NotNull(bindingSourceContext);
        ObjectProperty = ExpressionHelper.GetPropertyName(objectProperty);
    }

    public DataBinderControlContext<TDataSource, TProperty> Control<TControl>(TControl control, Expression<Func<TControl, TProperty>> property)
        where TControl : Control
    {
        var controlPropertyName = ExpressionHelper.GetPropertyName(property);
        control.DataBindings.Add(controlPropertyName, BindingSourceContext.DataSource, ObjectProperty, true);

        return this;
    }
}

public static class ExpressionHelper
{
    public static string GetPropertyName<TResult>(Expression<Func<TResult>> property)
    {
        return GetMemberNames(((LambdaExpression)property).Body).Skip(1).Join(".");
    }

    public static string GetPropertyName<T, TResult>(Expression<Func<T, TResult>> property)
    {
        return GetMemberNames(((LambdaExpression)property).Body).Join(".");
    }

    static IEnumerable<string> GetMemberNames(Expression expression)
    {
        if (expression is ConstantExpression || expression is ParameterExpression)
            yield break;

        var memberExpression = (MemberExpression)expression;

        foreach (var memberName in GetMemberNames(memberExpression.Expression))
            yield return memberName;

        yield return memberExpression.Member.Name;
    }
}

public static class StringExtentions
{
    public static string Join(this IEnumerable<string> values, string separator)
    {
        if (values == null)
            return null;

        return string.Join(separator, values.ToArray());
    }
}