I have a command that shows a view model:
private void DoShowImportCommand()
{
this.ShowViewModel<GeometryImportViewModel>();
}
but I only want to execute it if that view model isn't already shown. Is there a way to
detect if that view model is already on screen and if so don't execute the command?
MvvmCross doesn't track this by default - what is currently shown depends on the UI and can be interpreted in different ways in different situations (popups, tabs, pivots, dialogs, back stacks, etc)
If you want to track this in your own application, you could do it using UI project components (e.g. custom presenters) or you could do it using a shared code component - e.g. you could add "alive" tracking to the Views/ViewModels (see the N=42 video on http://mvvmcross.blogspot.com) and could then use some service to track which viewmodels are shown.
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 am writing an app that runs from the browser. However, some model functions are also called from the Yii2 console. Therefore, I am getting errors when trying to access variables that are set in the GUI.
Is it possible to tell which mode I am in? Is there some environment variable automatically set, or should I just set some session variable in the console app to indicate the state?
You can use
if (Yii::$app instanceof \yii\console\Application)
for console, and
if (Yii::$app instanceof \yii\web\Application)
for web.
Correct variant
Yii::$app->request->isConsoleRequest
There is a simpler way to figure this out without going through the Yii objects
if (php_sapi_name() == "cli") {
return;
}
...and it works for all PHP scripts
...and it is lighter
By default for console:
Yii::$app->id == 'basic-console'
And for web application:
Yii::$app->id == 'basic'
Yii::$app->id stores the id of the loaded configuration params. By default for console application it is 'basic-console' and for web application it is 'basic' (defined in configuration file)
Yii2 provides a number of different classes for application's console and for those of type web. In addition to this division of the mode of operation of the classes, there are also a set of rules governing the organization of the code of the application. The first, fundamental, it is the respect of giving the MVC Model object information, to view the management interface with the user and, finally, to the controller the role of coordination among them. In your case it seems to sense that a piece of code runs in console but referring to classes that provide a Web interface. Probably because in some Model classes were introduced with functions with HTML or other code that should not be there. If you need two separate applications should precisely separate applications that use a type controls
yii\console\Controller
and another that uses controller type web
yii\web\Controller.
Obviously Model classes will be common and, thanks to separate controller, be sure to invoke View appropriate to the type of user interface in use. I Hope this could be useful.
Works for nginx and apache:
function isConsole()
{
return 'cli' == php_sapi_name() || !array_key_exists('REQUEST_URI', $_SERVER);
}
Pure PHP:
global $argv;
if (empty($argv)) {
// Browser mode
}
else {
// Cli mode
}
We have a windows phone 8 application in which we are using mvvm light having four , five views , and about same number of view models. One day we observed that the size of the application is increasing with usage and eventually reaches more than 100 mb and eventually crashes.After lot of testing what we are able to understand is that every time we navigate to a view , its instance is created and stored in the memory.It was observed that all the instances of the view and the view model are living in the memory and thus increasing the space on the ram. We also confirmed the same by defining finializer on view class and view model , on closing the application the finializer is called exactly the same number of times the page was navigated to. We are binding the datacontext of the view to respective view model in xaml. One of the main view has an ad control , so size increases very fast if user navigates to that view multiple times. How to resolve this issue. What I am unable to understand is the view should be destroyed once the user presses the back button, but this is not happening . Any help would be much appreciated.
We found a solution to this by adding below line of code to code behind.
protected override void OnNavigatedFrom(NavigationEventArgs e)
{
base.OnNavigatedFrom(e);
Messenger.Default.Unregister(this);
if (e.NavigationMode == NavigationMode.Back)
{
DataContext = null;
}
}
What we are doing above is that we are unregisterring all the message handlers for the page and assigning the DataContext to null. In our case the datacontext was assigned in the xaml only and messenge handlers were registered in the OnNavigatedTo event of the page. But what is still unclear that on navigating back from the page , the page object should have died automatically . And should this line of code be added to all the mvvm light project pages and if so then why is it not common practice.
The reason you are leaking View memory is because you are in some way subscribing to events of the ViewModel from inside your Views. Either refactor those subscriptions to be WeakEvent subscriptions or remove them inside your OnNavigatedFrom
Use an IOC Container to maintain a single instance of all the ViewModels.
One of the options would be to use SimpleIoc that comes with MVVM Light.
Best tutorial to learn MVVMLight SimpleIoc
I have an Android app which uses a SupportActionBar that contains a bunch of tabs. These tabs each have a fragment that in turn are connected to a ViewModel in my core project. This works great and when i start the app they are all initialized right away and setup correctly.
What i would like to do is to call on a method on one of these ViewModels from my main activity that contains all the tabs and fragments.
I read in another post that in WP you could cast the DataContext to the ViewModel but that might not work in Android. I haven't been able to do this, maybe because my DataContext is not the currently displayed ViewModel but the MainViewModel connected to my main activity. Or maybe it's not supposed to be done that way, i'm not sure.
I'm trying to do this:
var test = (MessagesViewModel)this.DataContext;
test.GetViewDataFromApi();
To update the data in the view when i press the tab. I can't use the Init function for this for example since the ViewModel isn't recreated everytime i show the view.
Are you trying to update some data in the tab's fragment when tab is selected?
If that's the case, one way to do it is to
1) handle the tab selection event to get the current tab(maybe using TabListener),
2) get the fragment (MvxFagment) in the selected tab
3) get the (IMvxViewModel) view-model from the fragment
4) call the method you need to update data on the view-model
I assume you are using a MvxFragment (https://github.com/MvvmCross/MvvmCross/blob/v3.1/Cirrious/Cirrious.MvvmCross.Droid.Fragging/Fragments/MvxFragment.cs?source=cc) so you can access the view-model from the MvxFragment's ViewModel property.
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