Re: use of properties - get - set

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Laurent Bugnion [MVP] napisał(a):
Hi,

Doug wrote:
Hi

I have been told about the following code:

private string boxLabel;

public string BoxLabel

{

get { return boxLabel;}

set {boxLabel = value;}

}

does this routine set the value of the private string to be the same as the value input by the public string or is it the other way? Could you please tell me in simple words what this is used for?

Thanks

doug

Properties are a way to control access to your private members. The example here above is very trivial, as it simply (set) copies the given value to the private member and (get) returns the private member without modifying it.

Often, the set part is used to check the given value in order to avoid later errors, or to simplify code. For example, you can do something like:

private string myString = "";

public string MyString
{
set
{
if ( value == null )
{
value = "";
}
myString = value;
}
}

This code ensures that the private member "myString" can never be set to null. This way, the code using myString doesn't need to check everytime to avoid null reference exception.

There are many other ways to use properties, but generally, you can say that they are used to control user's access to private members.

It is good practice to never return attributes, but always properties. The reason is that it allows later changes to your code without modifying the interface to your class. The code you posted, though trivial, follows that rule.

HTH,
Laurent

You can use Properties too if you need one way direction "communication with variables". For example

private string s;
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
public string Name
{
get {return s;}
}
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
code above allows you to only read value of s, not to write(!).

Another idea is to combine return result depending on many than one variable.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
private bool var1, var2, var3;

.... // some code to modify values (i.e. test with aswer true or false)

public string TestResult
{
get
{
if((var1 && var2) || (var1 && var3) || (var2 && var3))
return "Test passed successfully";
else
return "You need to try again, good luck!";
}
}
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Generally what for you use properties ... it is up to you. It could only return or set value from variable, raise event (before or after settings a variable), get/set values to group of variables (like methods), test something and many more.

best,
Sławomir
.

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