I've a class which does not have a base class nor implements INotifyPropertyChanged.
In my application one object of this class is used as the viewmodel for 2 views (master and detail).
If I create the bindings to the properties by convention (x:Name). I see that when I change a property in the detail view it is also updated in the master.
This does not happen when I use the normal binding syntax.
Can anyone explain me why this happens ? Is this a feature of Caliburn.Micro ? I couldn't find it in the documents.
=== edit ==
I just found out that when using normal binding that the other view also get's updated only after the text box loses focus.
Still the question remains how can a View react to a change in the viewmodel when propertychanged is not implemented.
Thanks in advance,
Marwijn.
Caliburn.Micro binds properties with BindingMode.TwoWay by default.
If you did not specify this explicitly in your own binding - you've used OneWay.
Related
I have a very common problem, but I couldn't find any valid solution.
I want to create a Button able to contain more than a simple Label or Image. In fact, Xamarin Button exposes only Text and Image properties, but in my case I want to construct a more flexible set of controls (e.g. a StackPanel with a list of controls).
I implemented a ContentView acting as a Button after having added TapGestureRecognizer and it works from the pure functional point of view. What I don't like is the missing of all Visual States of a Button.
Therefore, I was thinking how to implement a Custom Renderer of a Button. I would like to expose a ContentPresenter BindableProperty and then set that property to the Button.Content (speaking in UWP terms) in the Renderer class. I think this could be a solution, the problem is that I don't know how to "cast" a Xamarin.ContentPresenter to a UWP.ContentPresenter. Do you have any idea about how to implement a Button able to contain any generic Content?
I'm migrating a cell-based NSTableView to be view-based. With NSCell, to determine if a cell was highlighted (e.g., to draw the text in white instead of black), I looked at the NSCell highlighted property.
What's the NSView version of this? I can't find anything like this in the docs.
The easiest way to do this is to simply subclass NSTableCellView. All the documentation says that you can subclass either NSTableCellView or NSView, e.g., Table View Programming Guide for Mac:
Drag an NSTableCellView object (or a custom view) from the object library to the appropriate column in the table view. ... Typically, the view class is a subclass of NSTableCellView.
It doesn't say what this is, or why you'd want to use it. It looks like an NSView which has an NSTextField and an NSImageView, and that's it -- so if you're not making a view that has these, it's tempting to ignore this class and just subclass NSView.
Interestingly, though, if you have any NSTextFields in an NSTableCellView (even if you don't use the textField property for this!), they automatically use the correct light/dark coloring.
In particular, it seems that the backgroundStyle property of NSTableCellView is what causes the text value to actually change. The documentation says:
The default implementation automatically forwards calls to all subviews that implement setBackgroundStyle: or are an NSControl, which have NSCell classes that respond to setBackgroundStyle:.
NSTextField is an NSControl with an NSCell, of course, so it gets this called on it.
While it's not exactly clear in Apple's documentation (what does "this" refer to?), it seems that NSTableView calls -setBackgroundStyle: on any view that defines it. So if you don't want to subclass NSTableCellView, you can alternatively just add a property to your own NSView:
var backgroundStyle: NSBackgroundStyle
and have your drawing code use that.
I have some custom ViewCell elements and most of them show and hide some components according to some properties of the BindingContext. I need to check values of some properties and show and hide some elements in the ViewCell, and also adjust the cell height accordingly.
Instead of writing value converters for most of the properties, I convert the BindingContext to underlying type and check the values of the properties in the OnBindingContextChanged event and right after that I build the UI with the relevant controls.
Do you think this is a bad way? Or is it ok?
I think it sounds quite counter-intuitive with regards to the MVVM model. Would you not be best binding the IsVisible property of the controls to a property determined in the ModelView?
e.g.
var label = new Label();
label.setBinding<ViewModel>(Label.IsVisibleProperty, vm => vm.IsLabelVisible, BindingMode.TwoWay);
You can then control the value of the IsLabelVisible property within the ViewModel instance.
One gotcha to consider is draw cycles and I would advise wrapping elements with toggled visibility states in Layout class.
Take a look at DataTemplateSelector pattern (similar to WPF):
http://forums.xamarin.com/discussion/comment/66502/#Comment_66502
I have a flex 3 datagrid that is in a completely separate container from the object that I am trying to reference it from - i.e. the datagrid is in a vbox, and I am trying to set a property in the datagrid from a popup.
How do I access the datagrid from the popup?
I'd like to do something like:
myView.myDatagrid.resizableColumns = false;
Using cairngorm as a framework if that is of any help.
You'll have to explain your architecture better to get a specific answer. This answer may help as everything I said about running methods on another component, also applies to accessing properties.
One solution for you is to pass the DataGrid instance into the popup as an instance variable; then the PopUp will be able to change the DataGrid's properties easy.
When you add your popup, you need to listen for an event. Then your PopUp needs to dispatch an event that the parent can handle.
myPopup.addEventListener(SomeEvent.DISABLE_COLUMNS,disableResize);
and then in the parent component
public function disableResize(event:SomeEvent):void{
myDatagrid.resizableColumns = false;
}
This assumes a custom event called SomeEvent... you can actually just create a default Flash event and give it a name like
dispatchEvent(new Event("MyDisableResizeEvent"));
Assuming you've got a button in your popup:
<mx:Button click="{dispatchEvent(new Event('MyDisableResizeEvent'));}" label="Disable Resizing"/>
I have two mxml files. one is main that is application tag mxml file and another is my mxml component file.
I have a viewstack in my main mxml whose id is, say, "mainViewStack".
Now I want to set selectedChild property of "mainViewStack" from my mxml component file.
But I m getting error:
Error #1009: Cannot access a property or method of a null object reference.
on accessing mainObj.mainViewStack.selectedChild.id where mainObj is the object of main mxml file.
Please help me out.
Thank u.
My guess is that you're trying to access the child before it's created. But that's hard to tell without the code.
Try waiting until the FlexEvent.CREATION_COMPLETE event on the application to access the selected child.
This issue is referred to as "deferred instantiation" and is a product of the Flex Component Lifecycle. If you want an extremely thorough explanation of this concept, this white paper is probably the best I have read.
Essentially Flex creates components as they are needed. Each component has a lifecycle that takes it through stages:
Construction
Addition
Initialization
Invalidation
Validation
Update
Removal
A sub-component isn't going to be accessible until it has passed through the initialization phase. This is the point at which a Flex component will dispatch its CREATION_COMPLETE event, letting you (and the framework) know that it is ready for interaction. Prior to this event, you are going to receive null reference errors when attempting to access the component or its children.
ViewStacks compound this by default by not initializing sub-components until they are called for display. The creationPolicy property of a ViewStack, by default, is set to auto. There are several options for this property, including all. Be aware, however, that this can potentially present severe performance issues, as all of the components inside the stack are going to be initialized immediately regardless of whether or not the user actually even looks at the component.
In your specific case this isn't the problem. The component that contains the view stack hasn't been completely initialized. You need to set the child of the ViewStack in a CREATION_COMPLETE event handler.
or you can give "creationPolicy=all" because Flex only creates the first visible child from the viewstack
You can use this code in your MXML component to change application's ViewStack selected child from other MXML component. However it is not a good practice.
FlexGlobals.topLevelApplication.mainViewStack.selectedChild = FlexGlobals.topLevelApplication.childId
You can use static event dispatcher to dispatch an event from one view and listen that event in an other view.