How to use MvvmCross without storyboards in iOS? - xamarin

When I was using MvvmCross 5, I coded all my views and avoided using storyboards for my iOS app by writing this in my AppDelegate:
[Register("AppDelegate")]
public class AppDelegate : MvxApplicationDelegate
{
private MvxIosViewPresenter viewPresenter;
public override UIWindow Window
{
get;
set;
}
/// <summary>
/// MvvmCross Mods:
/// - Creates a new presenter, which determines how Views are shown
/// - This example uses a standard presenter.
/// </summary>
/// <param name="application"></param>
/// <param name="launchOptions"></param>
/// <returns></returns>
public override bool FinishedLaunching(UIApplication application, NSDictionary launchOptions)
{
// create a new window instance based on the screen size
Window = new UIWindow(UIScreen.MainScreen.Bounds);
// MvvmCross Mod Start---------------------------------------------
// This class will determine how Views are shown
this.viewPresenter = new MvxIosViewPresenter(this, Window);//new ViewPresenter(Window);
// Init the Setup object, which initializes App.cs
var setup = new Setup(this, this.viewPresenter);
setup.Initialize();
//this.viewPresenter.PresentModalViewController(new ListenViewController(), true);
// Use IoC to find and start the IMvxAppStart object
var startup = Mvx.Resolve<IMvxAppStart>();
startup.Start();
// MvvmCross Mod End--------------------------------------------------
// make the window visible
Window.MakeKeyAndVisible();
return true;
}
public class Setup : MvxIosSetup
{
public Setup(MvxApplicationDelegate appDelegate, IMvxIosViewPresenter presenter)
: base(appDelegate, presenter)
{
}
protected override IMvxApplication CreateApp()
{
return new Core.App();
}
protected override IMvxTrace CreateDebugTrace()
{
return new DebugTrace();
}
}
But in MvvmCross 6.4.2, MvxIosSetup does not have the base constructor that takes 2 arguments. Instead I have:
[Register(nameof(AppDelegate))]
public partial class AppDelegate : MvxApplicationDelegate<Setup, App>
{
}
public class Setup : MvxIosSetup<App>
{
}
How can I configure it so that I can code my views without storyboards?
EDIT
I created a very small sample app with 1 view model/controller, using MvvmCross 7. The ViewDidLoad method never gets called in my MainViewController. Can someone please tell me why? I put my code here:
https://github.com/sinight95/TestApp/tree/main/TestApp

Neither the Setup.cs nor AppDelegate.cs files have anything to do whether you are presenting a storyboard or not. It is usually all up to which Presentation Attributes you are applying to a ViewController.
However, there are some stuff set in the Info.plist that changes how MvvmCross expects things to be set up.
Now in your example App you've put up on GitHub, you can do the following to make it not use the storyboard:
Remove Main.storyboard
In Info.plist set Main interface to (none)
In Info.plist set launch images to LaunchScreen.storyboard
Remove the scene delegate stuff in Info.plist
Remove the constructor in MainViewController
What is the main issue here is that you are essentially telling iOS that the ViewController has a storyboard by supplying this constuctor:
public MainViewController() : base(nameof(MainViewController), null)
{
}
Also are telling iOS to use storyboards through the Info.plist with all the scene delegation stuff.
I've created a PR showing what needs to be changed to make it run without the storboard and show the blue background color you've set on your ViewController.
https://github.com/sinight95/TestApp/pull/1

Related

Failed to instantiate the default view controller for UIMainStoryboardFile

I am writing a small sample app with Xamarin and MvvmCross 6.4.2. I completed the Xamarin.Android version and am now starting the Xamarin.iOS version. I created a view controller for the first screen:
public class SignInViewController : MvxViewController<SignInViewModel>
{
public SignInViewController() : base(nameof(SignInViewController), null)
{
}
public override void ViewDidLoad()
{
// never gets called...
base.ViewDidLoad();
}
}
When I run the app, I just get a blank screen and ViewDidLoad never gets called. In the application output it says:
Failed to instantiate the default view controller for
UIMainStoryboardFile 'Main' - perhaps the designated entry point is
not set?
My Main.storyboard is blank and I tried to modify it in Xcode Interface Builder to set my SignInViewController as the entry point, but I couldn't figure out how.
Failed to instantiate the default view controller for
UIMainStoryboardFile 'Main' - perhaps the designated entry point is
not set?
This error happens due to a simple mistake in your storyboard. When your app starts, iOS needs to know precisely which view controller needs to be shown first – known as your default view controller.
To fix it, add a ViewController to your Main.Storyboard and set it as Inital View Controller.
Refer: how-to-fix-the-error-failed-to-instantiate-the-default-view-controller-for-uimainstoryboardfile
And there are two SignInViewController in your project.
Use this one:
public partial class SignInViewController : UIViewController
{
public SignInViewController (IntPtr handle) : base (handle)
{
}
public override void ViewDidLoad()
{
// never gets called...
base.ViewDidLoad();
View.BackgroundColor = UIColor.Red;
}
}
Update:

Xamarin.iOS - Unable to load view controller from within another view controller

I recently started developing using Xamarin, so I'm by no means an expert and have been stuck on this problem for a day or so now.
First of all, I am not using storyboards. I am creating my own custom views (xib) and loading them from code
I'm building a new Xamarin.iOS app and am attempting to load a view controller from within another view controller. Initially, I am loading the first controller from the AppDelegate like so:
public override bool FinishedLaunching(UIApplication application, NSDictionary launchOptions)
{
window = new UIWindow(UIScreen.MainScreen.Bounds);
appStartUpController = new AppStartUpController();
window.RootViewController = appStartUpController;
window.MakeKeyAndVisible();
return true;
}
This loads my AppStartUpController fine which is basically just a loading screen with a background image and loading animation while I make an API call in the background. Once the API call has completed, I want to load another view controller.
After the API call has completed, I attempt to load the next Controller like so:
var controller = new CityPickerViewController();
this.NavigationController.PushViewController(controller, false);
And here is my CityPickerViewController:
public partial class CityPickerViewController : UIViewController
{
CityPicker_View v;
public CityPickerViewController(IntPtr handle) : base(handle)
{
}
public CityPickerViewController ()
{
}
public override void ViewDidLoad()
{
base.ViewDidLoad();
v = CityPicker_View.Create();
this.View = v;
}
public override void ViewWillAppear(bool animated)
{
base.ViewWillAppear(false);
UIImage i = UIImage.FromFile("citypickbackground.jpg");
i = i.Scale(this.View.Frame.Size);
this.View.BackgroundColor = UIColor.FromPatternImage(i);
}
}
I'm probably missing something obvious here, but the CityPickerViewController will not load. If I put a break point within the code, the viewDidLoad / ViewWillAppear overrides never get hit.
I'm a rookie programmer and would definitely appreciate any tips on this. Thanks in advance!
Welcome to SO!
Try base.NavigationController.PushViewController(controller, true); instead since you don't have a local navigation controller.
There could also be an issue in your CityPickerViewController, so try a different ViewController if that doesn't work.

OnAppearing different on iOS and Android

I have found that on iOS, OnAppearing is called when the page literally appears on the screen, whereas on Android, it's called when it's created.
I'm using this event to lazily construct an expensive to construct view but obviously the Android behaviour defeats this.
Is there some way of knowing on Android when a screen literally appears on the screen?
You can use the event:
this.Appearing += YourPageAppearing;
Otherwise, you should use the methods of the Application class that contains the lifecycle methods:
protected override void OnStart()
{
Debug.WriteLine ("OnStart");
}
protected override void OnSleep()
{
Debug.WriteLine ("OnSleep");
}
protected override void OnResume()
{
Debug.WriteLine ("OnResume");
}
On Android, Xamarin.Forms.Page.OnAppearing is called immediately before the page's view is shown to user (not when the page is "created" (constructed)).
If you want an initial view to appear quickly, by omitting an expensive sub-view, use a binding to make that view's IsVisible initially be "false". This will keep it out of the visual tree, avoiding most of the cost of building it. Place the (invisible) view in a grid cell, whose dimensions are constant (either in DPs or "*" - anything other than "Auto".) So that layout will be "ready" for that view, when you make it visible.
APPROACH 1:
Now you just need a binding in view model that will change IsVisible to "true".
The simplest hack is to, in OnAppearing, fire an action that will change that variable after 250 ms.
APPROACH 2:
The clean alternative is to create a custom page renderer, and override "draw".
Have draw, after calling base.draw, check an action property on your page.
If not null, invoke that action, then clear it (so only happens once).
I do this by inheriting from a custom page base class:
XAML for each of my pages (change "ContentPage" to "exodus:ExBasePage"):
<exodus:ExBasePage
xmlns:exodus="clr-namespace:Exodus;assembly=Exodus"
x:Class="YourNamespace.YourPage">
...
</exodus:ExBasePage>
xaml.cs:
using Exodus;
// After creating page, change "ContentPage" to "ExBasePage".
public partial class YourPage : ExBasePage
{
...
my custom ContentPage. NOTE: Includes code not needed for this, related to iOS Safe Area and Android hardward back button:
using Xamarin.Forms;
using Xamarin.Forms.PlatformConfiguration.iOSSpecific;
namespace Exodus
{
public abstract partial class ExBasePage : ContentPage
{
public ExBasePage()
{
// Each sub-class calls InitializeComponent(); not needed here.
ExBasePage.SetupForLightStatusBar( this );
}
// Avoids overlapping iOS status bar at top, and sets a dark background color.
public static void SetupForLightStatusBar( ContentPage page )
{
page.On<Xamarin.Forms.PlatformConfiguration.iOS>().SetUseSafeArea( true );
// iOS NOTE: Each ContentPage must set its BackgroundColor to black or other dark color (when using LightContent for status bar).
//page.BackgroundColor = Color.Black;
page.BackgroundColor = Color.FromRgb( 0.3, 0.3, 0.3 );
}
// Per-platform ExBasePageRenderer uses these.
public System.Action NextDrawAction;
/// <summary>
/// Override to do something else (or to do nothing, i.e. suppress back button).
/// </summary>
public virtual void OnHardwareBackButton()
{
// Normal content page; do normal back button behavior.
global::Exodus.Services.NavigatePopAsync();
}
}
}
renderer in Android project:
using System;
using Android.Content;
using Android.Views;
using Android.Graphics;
using Xamarin.Forms;
using Xamarin.Forms.Platform.Android;
using Exodus;
using Exodus.Android;
[assembly: ExportRenderer( typeof( ExBasePage ), typeof( ExBasePageRenderer ) )]
namespace Exodus.Android
{
public class ExBasePageRenderer : PageRenderer
{
public ExBasePageRenderer( Context context ) : base( context )
{
}
protected override void OnElementChanged( ElementChangedEventArgs<Page> e )
{
base.OnElementChanged( e );
var page = Element as ExBasePage;
if (page != null)
page.firstDraw = true;
}
public override void Draw( Canvas canvas )
{
try
{
base.Draw( canvas );
var page = Element as ExBasePage;
if (page?.NextDrawAction != null)
{
page.NextDrawAction();
page.NextDrawAction = null;
}
}
catch (Exception ex)
{
// TBD: Got Disposed exception on Android Bitmap, after rotating phone (in simulator).
// TODO: Log exception.
Console.WriteLine( "ExBasePageRenderer.Draw exception: " + ex.ToString() );
}
}
}
}
To do some action after the first time the page is drawn:
public partial class YourPage : ExBasePage
{
protected override void OnAppearing()
{
// TODO: OnPlatform code - I don't have it handy.
// On iOS, we call immediately "DeferredOnAppearing();"
// On Android, we set this field, and it is done in custom renderer.
NextDrawAction = DeferredOnAppearing;
}
void DeferredOnAppearing()
{
// Whatever you want to happen after page is drawn first time:
// ((MyViewModel)BindingContext).ExpensiveViewVisible = true;
// Where MyViewModel contains:
// public bool ExpensiveViewVisible { get; set; }
// And your XAML contains:
// <ExpensiveView IsVisible={Binding ExpensiveViewVisible}" ... />
}
}
NOTE: I do this differently on iOS, because Xamarin Forms on iOS (incorrectly - not to spec) calls OnAppearing AFTER the page is drawn.
So I have OnPlatform logic. On iOS, OnAppearing immediately calls DeferredOnAppearing. On Android, the line shown is done.
Hopefully iOS will eventually be fixed to call OnAppearing BEFORE,
for consistency between the two platforms.
If so, I would then add a similar renderer for iOS.
(The current iOS implementation means there is no way to update a view before it appears a SECOND time, due to popping the nav stack.
instead, it appears with outdated content, THEN you get a chance
to correct it. This is not good.)

MvvmCross - navigation with custom objects

I have followed the steps in this link
Passing complex navigation parameters with MvvmCross ShowViewModel
i implemented an instance of the IMvxJsonConverter, and registered it. this is my code for my view model
public class AccountDetailsViewModel : BaseViewModel<AccountDetailsNav>
{
private readonly Repository.AccountsRepository _accounts;
Account _fullAccount;
public AccountDetailsViewModel(Repository.AccountsRepository accounts)
{
_accounts = accounts;
}
protected override void RealInit(AccountDetailsNav parameter)
{
//stuff
}
I have tried simple types by just passing thru strings , this is the code i use to navigate to to the viewmodel
Mvx.RegisterSingleton<Repository.AccountsRepository>(() =>
{
return _accounts;
});
ShowViewModel<AccountDetailsViewModel>(nav);
But it never ever seems to arrive in my view model methods or populates my data, and i cannot for the life of me figure out why. the data is serialized fine , and i have even tried blank constructors to no avail .. i just cannot figure out why its not hitting the realinit
K i found the problem , when adding a new view i failed to remove this method on the code behind of the view, and as such was causing my viewmodel to be null and never hitting my breakpoints
/// <summary>
/// Invoked when this page is about to be displayed in a Frame.
/// </summary>
/// <param name="e">Event data that describes how this page was reached.
/// This parameter is typically used to configure the page.</param>
protected override void OnNavigatedTo(NavigationEventArgs e)
{
}

Monotouch Dialog OwnerDrawnElement - Height Size not being called

I am trying to inherit from OwnerDrawnElement (as presented in the docs). Everything seems to be working except the Height method is never called so I am not able to set the height of the cell. The Height method is never called (breakpoint never hits). I tried to force a reimplementation of IElementSizing and implemented the method again as a new method. Again, that also doesn't get hit. Here is the stripped down code
public class CustomDrawElement : OwnerDrawnElement, IElementSizing
{
public CustomDrawElement (UITableViewCellStyle style, string cellIdentifier) : base (style, cellIdentifier)
{
}
#region implemented abstract members of OwnerDrawnElement
public override void Draw (System.Drawing.RectangleF bounds, MonoTouch.CoreGraphics.CGContext context, MonoTouch.UIKit.UIView view)
{
UIColor.Blue.SetFill ();
context.FillRect (bounds);
}
public override float Height (System.Drawing.RectangleF bounds)
{
return 220f;
}
#endregion
public new float GetHeight (UITableView tableView, NSIndexPath indexPath) {
return 220f;
}
}
When creating the object, I using for test purposes only:
var e = new CustomDrawnElement(UITableViewCellStyle.Default, "myKey");
I am currently using the latest Xamarin Studio 3.
I have read every question regarding this class and no one seems to have had this problem. Not sure if it is due to the new 3 release that introduced a new bug.
Ok, after much research, I found the answer. In order for the custom height methods to be called, you need to set UnevenRows = true on the rootElement created for MonoDialog.

Resources