MvvmCross: App crash with missing constructor on MvxImageView

It seems that the optional parameter added to some/most of the MvxImageView constructors will make the app crash when Activator.CreateInstance is called by MvxAndroidViewFactory due to it not being able to find the proper constructor on MvxImageView.

The constructors changed in this commit: https://github.com/MvvmCross/MvvmCross/commit/0b36189d8711d3bc5d666e6e6817c21bb6b36007#diff-f589bfb4a2af223a198d622ddfbb955b

This SO thread has some good information on Reflection & optional parameters: https://stackoverflow.com/questions/2421994/invoking-methods-with-optional-parameters-through-reflection Also this SO thread has some more specific information about Activator.CreateInstance: https://stackoverflow.com/questions/11002523/activator-createinstance-with-optional-parameters

Imho, there’s 2 ways to fix this, either change the mvximageview constructors (get rid of optional parametes) or change the way the instance is created in the MvxAndroidViewFactory.

Steps to reproduce

Use the InternetMinute sample, use package version in the sample (4.0.0-beta2) or upgrade to 4.4.0
Build & verify that the app starts ok
Upgrade the mvvmcross packages to 5.0.1
Clean the solution (important to do this), build & start the app, it crashes on load of the HomeView

Expected behavior

HomeView loads

Actual behavior

App crashes with unhandled exception:

06-05 19:18:43.712 I/MvxBind ( 7148):   1.49 Exception during creation of Mvx.MvxImageView from type MvvmCross.Binding.Droid.Views.MvxImageView - exception MissingMethodException: Constructor on type 'MvvmCross.Binding.Droid.Views.MvxImageView' not found.
06-05 19:18:43.712 I/MvxBind ( 7148): 	  at System.RuntimeType.CreateInstanceImpl (System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder binder, System.Object[] args, System.Globalization.CultureInfo culture, System.Object[] activationAttributes, System.Threading.StackCrawlMark& stackMark) [0x00213] in <3fd174ff54b146228c505f23cf75ce71>:0 
06-05 19:18:43.712 I/MvxBind ( 7148):   at System.Activator.CreateInstance (System.Type type, System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder binder, System.Object[] args, System.Globalization.CultureInfo culture, System.Object[] activationAttributes) [0x000a1] in <3fd174ff54b146228c505f23cf75ce71>:0 
06-05 19:18:43.712 I/MvxBind ( 7148):   at System.Activator.CreateInstance (System.Type type, System.Object[] args) [0x00000] in <3fd174ff54b146228c505f23cf75ce71>:0 
06-05 19:18:43.712 I/MvxBind ( 7148):   at MvvmCross.Binding.Droid.Binders.MvxAndroidViewFactory.CreateView (Android.Views.View parent, System.String name, Android.Content.Context context, Android.Util.IAttributeSet attrs) [0x00019] in D:\git\MvvmCross2\MvvmCross\Binding\Droid\Binders\MvxAndroidViewFactory.cs:42 
[0:] MvxBind:Error:  1.49 Exception during creation of Mvx.MvxImageView from type MvvmCross.Binding.Droid.Views.MvxImageView - exception MissingMethodException: Constructor on type 'MvvmCross.Binding.Droid.Views.MvxImageView' not found.
	  at System.RuntimeType.CreateInstanceImpl (System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder binder, System.Object[] args, System.Globalization.CultureInfo culture, System.Object[] activationAttributes, System.Threading.StackCrawlMark& stackMark) [0x00213] in <3fd174ff54b146228c505f23cf75ce71>:0 
  at System.Activator.CreateInstance (System.Type type, System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder binder, System.Object[] args, System.Globalization.CultureInfo culture, System.Object[] activationAttributes) [0x000a1] in <3fd174ff54b146228c505f23cf75ce71>:0 
  at System.Activator.CreateInstance (System.Type type, System.Object[] args) [0x00000] in <3fd174ff54b146228c505f23cf75ce71>:0 
  at MvvmCross.Binding.Droid.Binders.MvxAndroidViewFactory.CreateView (Android.Views.View parent, System.String name, Android.Content.Context context, Android.Util.IAttributeSet attrs) [0x00019] in D:\git\MvvmCross2\MvvmCross\Binding\Droid\Binders\MvxAndroidViewFactory.cs:42

Configuration

Version: 5.0.1

Platform:

iOS
Android
WPF
UWP

About this issue

Original URL
State: closed
Created 7 years ago
Comments: 15 (6 by maintainers)

Most upvoted comments

I don’t think it will, as the calling code:

var view = Activator.CreateInstance(viewType, context, attrs) as View;

Will search for a constructor that matches something like:

public MvxImageView(Context context, IAttributeSet attrs)

This constructor does not exist, due to the optional parameter. A quick fix would probably be to change this constructor:

        public MvxImageView(Context context, IAttributeSet attrs, Action afterImageChangeAction = null)
            : this(context, attrs, 0, afterImageChangeAction)
        { }

To these 2:

        public MvxImageView(Context context, IAttributeSet attrs)
            : this(context, attrs, 0)
        { }

        public MvxImageView(Context context, IAttributeSet attrs, Action afterImageChangeAction)
            : this(context, attrs, 0, afterImageChangeAction)
        { }

Whilst I’m personally not a fan of optional constructor parameters, I think the better fix would be to change the calling code that instantiates the object to pick the correct constructor.

rickjansen-dev on Jun 9, 2017