I have a class Bar that implements INotifyPropertyChanged. When setting the property CurrentFoo, I want to raise PropertyChanged if the value is changing. Foo implements IEquatable but not the == operator.
Currently my code looks like this:
public class Bar : INotifyPropertyChanged
{
// ...
private Foo fooValue;
/// <summary>
/// Gets or sets the active Foo
/// </summary>
/// <value>The active Foo.</value>
public Foo CurrentFoo
{
get
{
return this.fooValue;
}
set
{
// Notify listeners if value is changing.
if (null == this.fooValue && null != value
|| null != this.fooValue && null == value
|| null != this.fooValue && null != value && !this.fooValue.Equals(value))
{
this.fooValue = value;
this.OnPropertyChanged("CurrentFoo");
}
}
}
// ...
}
And it woks, but...ugleh! Is there a more elegant/best-practices way of doing this check without restoring to the Null object pattern (inconsistent with the rest of our codebase)?
I've considered writing a utility method like IsOneObjectNullButNotBoth(object a, object b)...but again, blah. Surely I'm missing a handy-dandy class library method, though I already checked those.
Testing one of the values for null is enough, because the Equals method should return false if the argument is null:
if ((this.fooValue != value) ||
(this.fooValue != null && !this.fooValue.Equals(value)))
{
this.fooValue = value;
this.OnPropertyChanged("CurrentFoo");
}
Alternatively, you can use the default EqualityComparer for Foo which checks for nulls and calls the Equals method:
if (!EqualityComparer<Foo>.Default.Equals(this.FooValue, value))
{
this.fooValue = value;
this.OnPropertyChanged("CurrentFoo");
}
It seems like you could use an extension method here:
if(fooValue.IsChanged(value))
{
}
static public class Ext {
static public bool IsChanged(this Foo fooValue, Foo value) {
return null == fooValue && null != value
|| null != this.fooValue
&& null == value
|| null != this.fooValue
&& null != value
&& !this.fooValue.Equals(value));
}
}
This is built into the .net framework and will do just this
if (!System.Collections.Generic.EqualityComparer<Foo>.Default.Equals(value, fooValue))
{
// value changed logic here.
}
Well, may be this way:
Should work.
public Foo CurrentFoo
{
get
{
return this.fooValue;
}
set
{
// Notify listeners if value is changing.
bool bok = false;
if (this.fooValue !=null && !this.fooValue.Equals(value))
bok = true;
else if(this.fooValue ==null)
bok = (this.fooValue == value);
if(bok) {
this.fooValue = value;
this.OnPropertyChanged("CurrentFoo");
}
}
}
This is how I would write it if I didn't want to use EqualityComparer
:
if ((obj1 ?? obj2) != null && (obj1 == null || !obj1.Equals(obj2)))
{
// objects are diffrent
}
I think that's about as elegant as I can make it.
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