Unable to convert instance of type 'Android.Widget.Button'

Question

I got a weird exception comming up it worked for 1 year on android when i do:

TimerButton btnOut = FindViewById<TimerButton>(Resource.Id.btnTimer); 

it throws me an exception like:

System.InvalidCastException: Unable to convert instance of type 'Android.Widget.Button' to type 'MyProject.TimerButton'

The weird part is TimerButton inherits from Android.Widget.Button ? like:

public class TimerButton : Android.Widget.Button
{
        public int MaxTicks { get; set; }
        public EventHandler AfterTimer;
        private String OldButtonText { get; set; }

        public ButtonState State
        {
            get { return this._state; }
        }


    protected void Initialize()
    {
        if (MaxTicks == 0)
        { MaxTicks = 10; }

        OldButtonText = this.Text;

        this.Click += (sender, e) =>
        {
            if (this._state == GSDButtonState.Normal)
            {
                this.SetState(GSDButtonState.Ticking);
            }
            else
            {
                this.SetState(GSDButtonState.Normal);
            }
        };
    }

        public TimerButton(IntPtr javaReference, Android.Runtime.JniHandleOwnership transfer ) : base (javaReference, transfer)
        {
            this.Initialize ();
        }
        public TimerButton(Context context, Android.Util.IAttributeSet attrs) : base (context, attrs)
        {
            this.Initialize ();
        }

        public TimerButton (Context context, Android.Util.IAttributeSet attrs, int defStyle) : base (context, attrs, defStyle)
        {
            this.Initialize ();
        }
}

Its just a short example since im using this button with a custom eventhandler so i can do something in about x seconds. not important. So i stripped some code out such as SetState

Note this worked for like 1 year orso

What i tried:

• Project -> Clean
• Clean Bin and Obj folders of project
• recreate XML layout

if i use a simple button it won't crash. Resource.Id.btnTimer ofcourse exists in the XML layout as Button

pls does someone has any ideas or tips?

XML:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@drawable/background"
    android:minWidth="25px"
    android:minHeight="25px">
    <ScrollView
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:minWidth="25px"
        android:minHeight="25px">
        <LinearLayout
            android:orientation="vertical"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:minWidth="25px"
            android:minHeight="25px">
            <TextView
                android:text="Status"
                android:textAppearance="?android:attr/textAppearanceMedium"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:id="@+id/textView1" />
            <EditText
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:enabled="false"
                android:id="@+id/txtStatus" />
            <Button
                android:text="Timer Button"
                android:textColor="#FFFFFF"
                android:textSize="30sp"
                android:layout_width="fill_parent"
                android:layout_height="60dp"
                android:background="@drawable/ButtonState"
                android:shadowColor="#C4BEBE"
                android:layout_gravity="center"
                android:shadowDx="0"
                android:shadowDy="0"
                android:shadowRadius="5"
                android:layout_marginTop="10.1dp"
                android:layout_marginBottom="10.1dp"
                android:id="@+id/btnTimer" />

        </LinearLayout>
    </ScrollView>
</LinearLayout>

Answer 1

Change your Button in your layout to {your package name here}.TimerButton

Something like:

com.sushihangover.custombutton.XAMLButton

Example XAML:

<Button
    android:id="@+id/myButton"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="@string/hello" />
<com.sushihangover.custombutton.XAMLButton
    android:id="@+id/customButton"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="@string/hello" />

Note:

You must register your C#/Java wrappers so they have a fully qualified Java class name:

[Register("com.sushihangover.custombutton.XAMLButton")]
public class XAMLButton : Button

Answer 2

Your btnTimer is a Button not TimerButton. Replace <Button> with <MyProject.TimerButton>. Replace MyProject with the NameSpace of the TimerButton class.