Yes, I had the same problem.

For me, the solution was to do the following steps:
1. Clean all
2. Close IDE
3. Remove all bin and obj folders from all projects (shared and device specific)
4. Restart IDE, build and run

Hope this helps you.

I have created Xamarin Forms(Portable Class Library) project 2 weeks ago. And when i am going to compile it today, it gives such error:

Error 3 Exception while loading assemblies: System.IO.FileNotFoundException: Could not load assembly 'Xamarin.Android.Support.v4, Version=1.0.0.0, Culture=neutral, PublicKeyToken='. Perhaps it doesn't exist in the Mono for Android profile?
File name: 'Xamarin.Android.Support.v4.dll'
at Xamarin.Android.Tuner.DirectoryAssemblyResolver.Resolve(AssemblyNameReference reference, ReaderParameters parameters)
at Xamarin.Android.Tasks.ResolveAssemblies.AddAssemblyReferences(ICollection`1 assemblies, AssemblyDefinition assembly, Boolean topLevel)
at Xamarin.Android.Tasks.ResolveAssemblies.Execute() Epul.Android

maybe i have changed somethink. but not remember what.

What may be cause this error?

I would check your iOS .csproj file. Open it up in a text editor, look for those files and delete any references that shouldn't be there anymore.

Don't forget the PropertyChanged event

To be able to access the views data, You will want to create a property in your ViewModel.

For example, To get the Username from an Entry I would create property in ViewModel..

private string _username;
        public string Username
        {
            get {  return _username; }
            set {  _username = value; }
        }

and then bind it to the TextProperty on the Entry field and I can access it from the ViewModel.

First of all, this is a deprecated method of creating custom renderers. Check out the following link for more information on renderers:
https://docs.microsoft.com/en-us/xamarin/xamarin-forms/app-fundamentals/custom-renderer/entry

Second of all, your CustomEntry class needs to be public in order for your android project to see it. Clean, Rebuild, and all should be well. I would suggest investing some time on learning how assemblies work and especially access modification; it's need-to-know information!

it's push, not pop