Hide username on LoginDialog

[mgnslndh]

The LoginDialog can now be shown like this to hide the username and only ask for a password:

var result = await this.ShowLoginAsync("Authentication", "Enter your password", 
                                       new LoginDialogSettings 
                                       { 
                                           UsernameVisibility = Visibility.Collapsed
                                       });

Closes #2229

[punker76]

@mgnslndh thx, what if you set toVisibility=Hidden? then you got a empty line. is this good? maybe a short bool like HideUsername could be better. what do you think?
/cc @thoemmi

[mgnslndh]

Good point. I went for Visibility mostly because NegativeButton used it. But that does not mean it is appropriate for the Username of course.

HideUsername is better. True value results in Collapsed visibility, otherwise Visible.

[mgnslndh]

@punker76 HideUsername would require a custom BooleanToVisibilityConverter that inverts conversion (true => Collapse and false => Visible).

Is this OK, or should we use another property name like ShowUsername or IsUsernameVisible instead?

One solution could be to use HideUsername in the LoginDialogSetting but use Visibility for the dependency property. What do you think?

[thoemmi]

LoginDialogSettings should not have a property of type Visibility, that's an implementation detail. Use bool instead.

In general flags should be false by default, so IsUsernameHidden or ShouldHideUsername would be approriate. If that requires a new IConverter, well, it's easily written.

Collapsed is better than Hidden so no screen estate is preserved.

[punker76]

@mgnslndh can you change your PR to the suggestions?

[mgnslndh]

@punker76 @thoemmi I can change the PR and use a bool for the property on LoginDialogSettings, but I'd like your feedback on the dependency property type. Should it also be bool like on the LoginDialogSettings property or can it be of the type Visibility in which case we do not need a IValueConverter.

[mgnslndh]

@punker76 I've addressed the suggestions. Does it look OK?

[punker76]

@mgnslndh i merged your changes, but removed your converter and uses the new VisibilityHelper property IsCollapsed.

/cc @thoemmi