Runtime Type casting without generics

Question

This code works. But noticing the similarity between the 6th & 10th line,

void someThing_Click(object sender, RoutedEventArgs e)
{
    President pres;                
    if (e.GetType() == typeof(MouseButtonEventArgs))
    {
         pres = (sender as SomeUserControl ).DataContext as President;
    }
    else
    {
         pres = (sender as MenuItem ).DataContext as President;
    }
}

is there a way to shorten the code like,

Type t = (e.GetType() == typeof(MouseButtonEventArgs)) ? SomeUserControl : MenuItem;
pres = (sender as t).DataContext as President;

the code above doesn't work, just for illustration.

Use "as" operator only if you will check the result of it. In other cases, you should use normal cast (Type) operator - it has better performance. — GrzegorzM, Apr 10 '14 at 11:40
"normal"(direct) cast isn't faster, internally it uses combination of [is] and [as] operators. please have a look at my comment to @xxMUROxx answer — Andrew, Apr 10 '14 at 11:50

score 4 · Answer 1 · answered Apr 10 '14 at 11:40

4

I think no need of checking type of event args and all, this should be enough

President pres = ((FrameworkElement)sender).DataContext as President;

answered Apr 10 '14 at 11:40

Sriram Sakthivel

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Rohit Vats · Answer 2 · 2014-04-10T11:46:45.430

2

DataContext property is of class FrameworkElement i.e. your SomeUserControl and MenuItem inherit from FrameworkElement. So you can type cast it to FrameworkElement directly:

pres = ((FrameworkElement)sender).DataContext as President;

edited Apr 10 '14 at 11:46

answered Apr 10 '14 at 11:40

Rohit Vats

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This is semantically different from OP's code, you missed else part; though if block itself completely redundant – Sriram Sakthivel Apr 10 '14 at 11:42
No need for if I guess, he get President for both cases – Arsen Mkrtchyan Apr 10 '14 at 11:42
@Sriram - I hope the intent was clear from the description. Any ways remove the else part. – Rohit Vats Apr 10 '14 at 11:45
Rohit, that's clear indeed but when you use `if` without else semantics of the code will be changed if `e` is not of type `MouseButtonEventArgs`. That's my point. – Sriram Sakthivel Apr 10 '14 at 11:47

score 2 · Answer 3 · answered Apr 10 '14 at 11:40

2

Directly use DataContext from FrameworkElement

var fe = sender as FrameworkElement
if(fe != null)
{
    President pres = fe.DataContext as President;
}

answered Apr 10 '14 at 11:40

Michael Mairegger

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Combination of [as] and comparison with null is the most effective way of doing certain type job with untyped object.(direct cast first checks with [is] and then either throws exception or returns object casted with the use of [as] operator, that is one extra [is] operation) – Andrew Apr 10 '14 at 11:48
@Andrew Point 1 agreed, but I disagree that `direct cast first checks with [is] and then either throws exception or returns object casted with the use of [as] operator, that is one extra [is] operation` can you show a official documentation for this? Or any provable link? – Sriram Sakthivel Apr 10 '14 at 11:52
for example here: http://stackoverflow.com/questions/496096/casting-vs-using-the-as-keyword-in-the-clr direct cast is internally translated to `if (variable is T){ return (variable as T)} throw.... ` – Andrew Apr 10 '14 at 12:01
I did some maths(kind of load test) in the past...try doing the same: a million of direct cast operations versus million of [is]-[as] combinations – Andrew Apr 10 '14 at 12:07
another good one: http://www.codeproject.com/Articles/8052/Type-casting-impact-over-execution-performance-in – Andrew Apr 10 '14 at 12:10

Runtime Type casting without generics

3 Answers3