Change Cursor on Android with Xamarin Forms Visual

Question

I have a Xamarin Forms Android application with the Material Design Visual. That seems to override the cursor color to black. Now I would like to create a dark theme. On IOS the cursor color changes with the font color to white. But on Android it stays black which makes it barely visible. Is there a way that I can override the color set as the cursor color?

Based on this Forum discussion I tried this Effect: https://forums.xamarin.com/discussion/42823/change-entry-cursor

    protected override void OnAttached()
    {
        try
        {
            IntPtr IntPtrtextViewClass = JNIEnv.FindClass(typeof(TextView));
            IntPtr mCursorDrawableResProperty = JNIEnv.GetFieldID(IntPtrtextViewClass, "mCursorDrawableRes", "I");
            JNIEnv.SetField(Control.Handle, mCursorDrawableResProperty, Resource.Drawable.custom_cursor);
        }
        catch (Exception e) {
            Console.WriteLine(e);
        }
    }

cursor drawable:

<shape xmlns:android="http://schemas.android.com/apk/res/android"
       android:shape="rectangle">

  <solid android:color="@color/colorAccent"></solid>
  <size android:width="2dp" />

</shape>

But with that the app crashes with the following error in the output:

JNI DETECTED ERROR IN APPLICATION: jfieldID int android.widget.TextView.mCursorDrawableRes not valid for an object of class md5a6256f8d5bc17d3565a450e514d4a6e7.MaterialFormsTextInputLayout

Xamarin Forms doesn't expose any api for control cursor color, you would have to create an Effect to change that behavoir. — FabriBertani
@FabriBertani Thanks for your response! I tried to create an effect, but so far no success. I added the last version to my original post. Maybe you have an idea what is wrong. — NPadrutt
Could you please post the demo of the effect you have you tried ? — Jessie Zhang -MSFT

NPadrutt NPadrutt · Accepted Answer · 2019-07-25T11:27:31

I ended up with a custom renderer for the entry.

[assembly: ExportRenderer(typeof(Entry), typeof(CustomEntryRenderer), new[] { typeof(VisualMarker.MaterialVisual) })]
namespace MoneyFox.Droid.Renderer
{
    public class CustomEntryRenderer : MaterialEntryRenderer
    {
        public CustomEntryRenderer(Context context) : base(context) {
        }

        protected override void OnElementChanged(ElementChangedEventArgs<Entry> e) {
            base.OnElementChanged(e);

            // set cursor color
            IntPtr IntPtrtextViewClass = JNIEnv.FindClass(typeof(TextView));
            IntPtr mCursorDrawableResProperty = JNIEnv.GetFieldID(IntPtrtextViewClass, "mCursorDrawableRes", "I");

            JNIEnv.SetField(Control.EditText.Handle, mCursorDrawableResProperty, Resource.Drawable.CustomCursor);

            // try set cursor pointer color
            try
            {
                TextView textViewTemplate = new TextView(Control.EditText.Context);

                var field = textViewTemplate.Class.GetDeclaredField("mEditor");
                field.Accessible = true;
                var editor = field.Get(Control.EditText);

                String[]
                    fieldsNames = { "mTextSelectHandleLeftRes", "mTextSelectHandleRightRes", "mTextSelectHandleRes" },
                    drawablesNames = { "mSelectHandleLeft", "mSelectHandleRight", "mSelectHandleCenter" };

                for (Int32 index = 0; index < fieldsNames.Length && index < drawablesNames.Length; index++)
                {
                    String
                        fieldName = fieldsNames[index],
                        drawableName = drawablesNames[index];

                    field = textViewTemplate.Class.GetDeclaredField(fieldName);
                    field.Accessible = true;
                    Int32 handle = field.GetInt(Control.EditText);

                    Drawable handleDrawable = Resources.GetDrawable(handle, null);

                    handleDrawable.SetColorFilter(Color.Accent.ToAndroid(), PorterDuff.Mode.SrcIn);

                    field = editor.Class.GetDeclaredField(drawableName);
                    field.Accessible = true;
                    field.Set(editor, handleDrawable);
                }
            } 
            catch (Exception ex)
            {
                LogManager.GetCurrentClassLogger().Error(ex);
            }
        }
    }
}

There I was able to call Control.EditText.Handle, which accesses the native control. Unfortunately this is not accessible for effects.

Change Cursor on Android with Xamarin Forms Visual

1 Answers