I repeat this property in my MVVM project too many times to count. What would be the correct way to create a generic class or factory to replace these lines of code?
ObservableCollection<Result> _resultCollection;
public ObservableCollection<Result> ResultCollection
{
get
{
if (_resultCollection == null)
_resultCollection = new ObservableCollection<Result>();
return _resultCollection;
}
set
{
_resultCollection = value;
}
}
I know this doesn't exactly answer your question, however personally I prefer to use a recorded macro in Visual Studio that writes all that for me.
I prefer using this to a generic class as it keeps all the relevant code in one place, and it's easy to understand what is going on. Typically I put all my private Fields at the top of my class, and hide all the public Properties in a #region tag that I keep collapsed so I don't need to scroll through them.
It's fairly easy to create a macro in VS: Simply go to Tools > Macros > Record Temporary Macro, then perform the changes you want using the keyboard only. Once you have the Macro working correctly, simply save it as a permanent macro. If you do it right, you can re-run the macro with any variable and it will build it out the same way.
Some useful keyboard shortcuts to remember when creating macros are:
- Ctrl+C/Ctrl+V to copy/paste
- Ctrl+Right/Ctrl+Left to move over a word
- Home/End to move to the beginning or end of a line
- Shift for highlighting words as you move the cursor
You may also need to do some minor modifications to the VB macro code, such as a .Replace() to turn lowercase letters to capitals.
Here's an example Macro I use to build out all my public Properties for MVVM. It uses the PRISM library, so it uses the syntax RaisePropertyChanged(() => this.SomeProperty);
Sub PRISM_BuildPropertyChanged_CursorAtDefaultAfterCtrlRE()
DTE.ActiveDocument.Selection.LineDown(False, 2)
DTE.ActiveDocument.Selection.WordLeft(True)
DTE.ActiveDocument.Selection.Copy()
DTE.ActiveDocument.Selection.LineDown(False, 3)
DTE.ActiveDocument.Selection.EndOfLine()
DTE.ActiveDocument.Selection.CharLeft()
DTE.ActiveDocument.Selection.NewLine()
DTE.ActiveDocument.Selection.Text = "RaisePropertyChanged(() => this."
DTE.ActiveDocument.Selection.Paste()
DTE.ActiveDocument.Selection.Text = ");"
DTE.ActiveDocument.Selection.LineUp()
DTE.ActiveDocument.Selection.StartOfLine(vsStartOfLineOptions.vsStartOfLineOptionsFirstText)
DTE.ActiveDocument.Selection.CharRight(False, 4)
DTE.ActiveDocument.Selection.NewLine()
DTE.ActiveDocument.Selection.CharRight()
DTE.ActiveDocument.Selection.NewLine()
DTE.ActiveDocument.Selection.Text = "if (value != "
DTE.ActiveDocument.Selection.WordRight(True)
DTE.ActiveDocument.Selection.Copy()
DTE.ActiveDocument.Selection.CharLeft()
DTE.ActiveDocument.Selection.Paste()
DTE.ActiveDocument.Selection.DeleteLeft()
DTE.ActiveDocument.Selection.Text = ")"
DTE.ActiveDocument.Selection.NewLine()
DTE.ActiveDocument.Selection.Text = "{"
DTE.ActiveDocument.Selection.LineDown()
DTE.ActiveDocument.Selection.EndOfLine()
DTE.ActiveDocument.Selection.NewLine()
DTE.ActiveDocument.Selection.Text = "}"
End Sub
With it, I can write my private definition, such as
private ObservableCollection<SomeObject> _someCollection;
Hit Ctrl+R, E to build the public property definition
private ObservableCollection<SomeObject> _someCollection;
public ObservableCollection<SomeObject> SomeCollection
{
get { return _someCollection; }
set { _someCollection = value; }
}
Then run my Macro to build out the Property Change notification
public ObservableCollection<SomeObject> SomeCollection
{
get { return _someCollection; }
set
{
if (value != _someCollection)
{
_someCollection = value;
RaisePropertyChanged(() => this.SomeCollection);
}
}
}
(By default, Ctrl+R, E puts the cursor at the end of the private field definition, so that is where the cursor needs to be when running this macro)
I also have another old macro that adds code that checks if the value is null, and if so sets it to a new instance of the object, but its one I never used much since I prefer to set my default definitions in the Constructor instead of in the Property definition.
If you want it, it looks like this (note the Macro name - You need to highlight the public property name prior to running this macro):
Sub CreatePublicGet_NoNull_HightlightPropertyNameFirst()
DTE.ActiveDocument.Selection.CharLeft(False, 2)
DTE.ActiveDocument.Selection.StartOfLine(vsStartOfLineOptions.vsStartOfLineOptionsFirstText, True)
DTE.ActiveDocument.Selection.WordRight(True)
DTE.ActiveDocument.Selection.Copy()
DTE.ActiveDocument.Selection.LineDown(False, 2)
DTE.ActiveDocument.Selection.StartOfLine(vsStartOfLineOptions.vsStartOfLineOptionsFirstText)
DTE.ActiveDocument.Selection.CharRight(False, 4)
DTE.ActiveDocument.Selection.NewLine()
DTE.ActiveDocument.Selection.CharRight()
DTE.ActiveDocument.Selection.NewLine()
DTE.ActiveDocument.Selection.EndOfLine()
DTE.ActiveDocument.Selection.CharLeft()
DTE.ActiveDocument.Selection.NewLine()
DTE.ActiveDocument.Selection.LineUp(False, 2)
DTE.ActiveDocument.Selection.EndOfLine()
DTE.ActiveDocument.Selection.NewLine()
DTE.ActiveDocument.Selection.Paste()
DTE.ActiveDocument.Selection.Text = "();"
DTE.ActiveDocument.Selection.LineDown()
DTE.ActiveDocument.Selection.WordLeft(True)
DTE.ActiveDocument.Selection.CharLeft()
DTE.ActiveDocument.Selection.WordLeft(True)
DTE.ActiveDocument.Selection.Copy()
DTE.ActiveDocument.Selection.LineUp(False, 2)
DTE.ActiveDocument.Selection.NewLine()
DTE.ActiveDocument.Selection.Text = "if ("
DTE.ActiveDocument.Selection.Paste()
DTE.ActiveDocument.Selection.Text = " == null)"
DTE.ActiveDocument.Selection.NewLine()
DTE.ActiveDocument.Selection.Text = "{"
DTE.ActiveDocument.Selection.LineDown()
DTE.ActiveDocument.Selection.StartOfLine(vsStartOfLineOptions.vsStartOfLineOptionsFirstText)
DTE.ActiveDocument.Selection.EndOfLine()
DTE.ActiveDocument.Selection.NewLine()
DTE.ActiveDocument.Selection.Text = "}"
DTE.ActiveDocument.Selection.LineUp()
DTE.ActiveDocument.Selection.StartOfLine(vsStartOfLineOptions.vsStartOfLineOptionsFirstText)
DTE.ActiveDocument.Selection.Paste()
DTE.ActiveDocument.Selection.Text = " = new "
DTE.ActiveDocument.Selection.Collapse()
DTE.ActiveDocument.Selection.EndOfLine()
DTE.ActiveDocument.Selection.LineDown(False, 4)
DTE.ActiveDocument.Selection.EndOfLine()
DTE.ActiveDocument.Selection.LineUp(True)
DTE.ActiveDocument.Selection.Delete()
End Sub
And results in code looking like this:
public ObservableCollection<SomeObject> SomeCollection
{
get
{
if (_someCollection == null)
{
_someCollection = new ObservableCollection<SomeObject>();
}
return _someCollection;
}
}
AFAIK it's not possible without some form of code generation. Look into T4 templates, as answered here
.
public abstract class XBase<T>
{
ObservableCollection<T> _resultCollection;
public ObservableCollection<T> ResultCollection
{
get
{
if (_resultCollection == null)
_resultCollection = new ObservableCollection<T>();
return _resultCollection;
}
set
{
_resultCollection = value;
}
}
}
Yea... to be able to bind to a field would be great, wouldn't it... ;-) This brings me to the first solution:
(1) create a converter that allows you to bind a field.
public class FieldBindingConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
var par = parameter as string;
var field = value.GetType().GetField(par);
return field.GetValue(value);
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
and then (2) binding the field directly from XAML:
<ItemsControl ItemsSource="{Binding ., Converter={StaticResource Field}, ConverterParameter=Coll2}" Grid.Row="1">
I kinda dislike this to be honest because it doesn't really clear things up... So as the second solution, you can instantiate the property directly from the constructor:
public Foo()
{
ResultCollection = new ObservableCollection<Result>();
}
[...]
public ObservableCollection<Result> ResultCollection { get; private set; }
While this does increase your memory footprint a few bytes (it changes the semantics of lazy instantiation into direct instantiation), I wouldn't be too concerned about that.
