From the Click event of a TextView\EditText in Xamarin Android I want to get at MVVMCross's Binding instance for that control.
I guess it would be the equivalent of GetBindingExpression in Windows Store SDK
How do I do that?
in MvvmCross, the bindings are stored in the binding context - not in the individual control. This is because the controls aren't natively Data-Binding aware.
The default context doesn't expose these bindings - see https://github.com/MvvmCross/MvvmCross/blob/bbf9a2ac76e74d9404f4b57036c6e29dfe2cc6c3/Cirrious/Cirrious.MvvmCross.Binding/BindingContext/MvxBindingContext.cs - but you could replace this with your own IMvxBindingContext if you needed to - this implementation could expose "search by control" or other iterator functionality.
Related
I have created a new solution for my MvvmCross app that supported Windows Store and I want to support UWP on Windows 10. I have moved over the PCL successfully, but I am having problems getting the basic UWP app working using a sample provided by MS (NavigationMenu) which uses the SplitView and the AppShell pattern they are recommending for the new navigation/command model. I referenced a helpful blog post (http://stephanvs.com/implementing-a-multi-region-presenter-for-windows-10-uwp-and-mvvmcross/), which gave me some guidance on how to integrate mvvmcross into the AppShell, but startup is failing because the AppShell does not have a valid Frame defined. Frame is a read-only property, and I have been unable to see where this is being set up.
I am using the standard AppShell implementation from the NavigationMenu with the following changes as recommended in the blog post:
public sealed partial class AppShell : MvxWindowsPage // was Page
public Frame AppFrame { get { return this.Frame; } } // was this.frame
Except for code after the error, there are no differences in the setup. In looking at the MvxWindowsPage implementation, there doesn't seem to be anything special as it still invokes the Page initialization. Is there something obvious I am missing?
So the link to the blogpost is correct, in other words you'll need to use MultiRegions from MvvmCross to get this working.
But what the blogpost doesn't show is a complete working version...
I've added one on my github here:
https://github.com/Depechie/MvvmCrossUWPSplitView
Some pointers to take away, like I said in the comments.
Your view where the SplitView will be present, needs to have a property to return a valid Frame to look for while injecting new views. This can be returned like this return (Frame)this.WrappedFrame.UnderlyingControl; found in the code here https://github.com/Depechie/MvvmCrossUWPSplitView/blob/master/MvvmCrossUWP.Win/Views/FirstView.xaml.cs#L13
Than all views you want to load up in the SplitView will need to reference to the region you defined in that SplitView, in my case I named it FrameContent as seen here https://github.com/Depechie/MvvmCrossUWPSplitView/blob/master/MvvmCrossUWP.Win/Views/FirstView.xaml#L48
So use that name for the region attribute in all to be loaded views like so [MvxRegion("FrameContent")] example here https://github.com/Depechie/MvvmCrossUWPSplitView/blob/master/MvvmCrossUWP.Win/Views/SecondView.xaml.cs#L7
I see what you're trying to do with the SplitView template that's provided by Microsoft. There is however a mismatch between things managed by MvvmCross and UWP.
By default MvvmCross maps ViewModels to Views based on naming conventions. What you are trying to do is use a view 'AppShell' (which is derived of Windows.UI.Xaml.Controls.Page) that doesn't adhere to the default MvvmCross convention.
The way I choose to implement this SplitView (Hamburger) functionality is by deleting the provided AppShell class entirely. I then created a new view named HomeView (since I have a ViewModel with the name HomeViewModel) and added the SplitView control there as described in the post you mentioned above.
For completeness I've created a Gist with the App.xaml.cs and HomeView.xaml as you requested. You can find them here: https://gist.github.com/Stephanvs/7bb2cdc9dbf15cb7a90f
I have done a RegisterAppStart<FirstViewModel>() in the Core App.cs, now I navigate to FirstViewModel, then SecondViewModel and finally ThirdViewModel using ShowViewModel(),
Is there a way I want to navigate to the viewmodel which has been registered using RegisterAppStart<>(), I mean is this persisted or saved somewhere during run?
All I want is to get this value at runtime.
If you want to use a singleton instance of a view model then you can do this using a custom view model locator - see the wiki - https://github.com/MvvmCross/MvvmCross/wiki/Customising-using-App-and-Setup - "overriding view model location and construction"
I am using Prism for Windows Runtime to help with my MVVM implementation. It has a built in SetProperty command for properties. How do I listen for a property change from within the View Model to make something else happen?
You can handle INotifyPropertyChanged.PropertyChanged event and check the name of the property. If you want to avoid string comparisons - you can define a new event and raise it for specific property. It can either be a regular CLR event or an EventAggregator one if you want to broadcast it to any interested listeners in the app.
I am trying to understand how MvvmCross manages memory on Windows Phone.
I try to mark my view and viewmodel as IDisposable, but the Dispose method is never called.
What I need to do is to make sure that I can free up some resources while my app is running location tracking in the background.
Christian
In MvvmCross:
each View references its ViewModel
the platform-specifiic operating system decides when to dereference the View - when this occurs it normally calls a method on the View (but this does depend on whether the view is a page, a tab, a flyout, a dialog, a custom control, etc)
the .Net or Mono Garbage Collector then decides when to collect both the Views and ViewModels from memory
If you want to do more "active" monitoring of when the View is visible for "page-level" Views, then you need to monitor "page-level" View-specific events like:
ViewDidAppear \ ViewDidDisappear \ removeFromParentViewController (iOS)
OnResume \ OnPause`OnFinish` (Droid)
OnNavigatedTo`OnNavigatedFrom` (Windows)
A generalised form of these events can then be easily called on a custom interface on your ViewModel (this can be IDisposable if you want - this is your application code).
Update: I have blogged about this and published a sample - see http://slodge.blogspot.co.uk/2013/11/n42-is-my-viewmodel-visible-can-i-kill.html
There's a bit more info on this in:
ViewModel LifeCycle, when does it get disposed? (see "There's no easy universal way to know when to dispose the ViewModel - especially once you start mixing and matching ViewModel presentation styles to include navigations, tabs, splitviews, flyouts, fragments, lists, etc. and as you include more and more platforms")
https://github.com/MvvmCross/MvvmCross/wiki/View-Model-Lifecycle#viewmodel-deactivation-activation-and-destruction
My good friend, Wikipedia, didn't give me a very good response to that question. So:
What are language bindings?
How do they work?
Specifically accessing functions from code written in language X of a library written in language Y.
Let's say you create a C library to post stuff to stackoverflow. Now you want to be able to use the same library from Python. In this case, you will write Python bindings for your library.
Also see SWIG: http://www.swig.org
In the context of code libraries, bindings are wrapper libraries that bridge between two programming languages so that a library that was written for one language can also be implicitly used in another language.
For example, libsvn is the API for Subversion and was written in C. If you want to access Subversion from within Java code you can use libsvn-java. libsvn-java depends on libsvn being installed because libsvn-java is a mere bridge between the Java programming language and libsvn, providing an API that merely calls functions of libsvn to do the real work.
Okay, now the question has been clarified, this isn't really relevant so I'm moving it to a new question
Binding generally refers to a mapping of one thing to another - i.e. a datasource to a presentation object. It can typically refer to binding data from a database, or similar source (XML file, web service etc) to a presentation control or element - think list or table in HTML, combo box or data grid in desktop software.
...If that's the kind of binding you're interested in, read on...
You generally have to bind the presentation element to the datasource, not the other way around. This would involve some kind of mapping - i.e. which fields from the datasource do you want to appear in the output.
For more information in a couple of environments see:
Data binding in .Net using Windows Forms
http://www.codeproject.com/KB/database/databindingconcepts.aspx
http://www.akadia.com/services/dotnet_databinding.html
ASP.NET data binding
http://support.microsoft.com/kb/307860
http://www.15seconds.com/issue/040630.htm
http://www.w3schools.com/ASPNET/aspnet_databinding.asp
Java data binding
http://www.xml.com/pub/a/2003/09/03/binding.html
Python data binding
http://www.xml.com/pub/a/2005/07/27/py-xml.html
General XML data binding
http://www.rpbourret.com/xml/XMLDataBinding.htm
In Flex (Actionscript 3). Source
A data binding copies the value of a property in one object to a property in another object. You can bind the properties of following objects: Flex components, Flex data models, and Flex data services.
The object property that provides the data is known as the source property. The object property that receives the data is known as the destination property.
The following example binds the text property of a TextInput component (the source property) to the text property of a Label component (the destination property) so that text entered in the TextInput component is displayed by the Label component:
<mx:TextInput id="LNameInput"></mx:TextInput>
...
<mx:Label text="{LNameInput.text}"></mx:Label>
Data binding is usually a simple way to bind a model to user interface components. For example, you have a class with a FirstName property. In flex you could easily bind that property to a textbox by setting the value of the textbox to {Object.FirstName}. Then, every time that FirstName property changes, the textbox will be updated without requiring you to write any code to monitor that property for changes.
Hope that helps.
Matt