Dynamically setting property inside own class

Question

I think I'm very close to have this figured out, but I haven't made progress for some time now and don't really have a choice but to ask around.

I have a GraphicsSettings class with a large set of graphics properties. These properties have a placeholder value with the property's name, which I use for a comparison loop.

The comparison loop is a function inside the class, and is between an array of the graphics properties and a Stringreader going over lines in an external text file.

When the loop finds a match between the value of a graphics property and a part of what is in a line, I want to set the entire value of the line into the graphics property.

Here's the problem though, I do not know how to call the property setter from within the class without specifically typing out it's name, which I cannot do since its a loop.

I've tried using:

this.GetType().GetProperty(key).SetValue(this,line, null);

Where "key" is the property name and "line" is the line value. From what I understand, this should work just fine when calling a class object from the outside to set a value, but it seems to be utterly against calling a class from the inside using this method.

All I get is a TargetInvocationException was unhandled error. Not too surprising, but I dont know how to get around this.

So I guess it comes down to this: How do I access a property through the use of a string, from inside the same class where the property resides?

I think you need to post some code, including the line that throws the exception, because this should be no issue. — John Willemse
– John Willemse, Commented Mar 4, 2013 at 12:38
Also, a TargetInvocationException can be quite deceptive. Be sure to check out all nested InnerExceptions, because most likely they will give you a better idea of the true, underlying cause. — John Willemse
– John Willemse, Commented Mar 4, 2013 at 12:44
There is no direct reason that line should fail assuming that key is in fact the property name (case sensitive) and that line doesn't break any type boundaries (e.g. setting null to an int). — Mike Perrenoud
– Mike Perrenoud, Commented Mar 4, 2013 at 12:57

Olivier Jacot-Descombes · Accepted Answer · 2013-03-04 14:01:27Z

4

If the properties are not public, you might need to use binding flags, because the GetProperty method does not know, that you are calling it from within the target class. C#'s accessibility rules apply to the static code text and do not apply here.

PropertyInfo prop = this.GetType().GetProperty(key, BindingFlags.Instance | 
                                                    BindingFlags.NonPublic);
prop.SetValue(this, "data", null);

Note that finding a property is case sensitive. Therefore you also might need to include the IgnoreCase flag.

PropertyInfo prop = this.GetType().GetProperty(key, BindingFlags.Instance |
                                                    BindingFlags.NonPublic |
                                                    BindingFlags.IgnoreCase);
prop.SetValue(this, "data", null);

If your properties were static, you would specify the BindingFlags.Static flag instead of BindingFlags.Instance flag. You can also combine both as well as BindingFlags.NonPublic | BindingFlags.Public for mixed cases.

Note also that the types must match. The implicit type conversions of C# do not work here. So always provide the correct type for the value parameter (second parameter) of SetValue. E.g.

string input = "123";
prop.SetValue(this, Int32.Parse(input), null);

int i = 77;
prop.SetValue(this, (double)i, null);

Also convert an int to a double explicitly, if the property is of type double.

Chris Kerekes suggests using prop.MemberType in conjunction with Convert.ChangeType to get a fully dynamic approach that will work if you have properties with different types (at least for the most common types).

prop.SetValue(this, Convert.ChangeType(line, prop.MemberType), null);

edited Mar 4, 2013 at 14:01

answered Mar 4, 2013 at 13:02

Olivier Jacot-Descombes

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2 Comments

Chris Kerekes Over a year ago

Great answer although I'd probably recommend conversion for clr types via prop.SetValue(this, Convert.ChangeType(line, prop.MemberType), null);

Olivier Jacot-Descombes Over a year ago

@Chris Kerekes: Yes, your solution allows a very dynamic approach.

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