Xamarin.Forms FindViewById() 返回 null

Question

I am trying to create a toast with a custom font, in my layout file in the android project i did:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <TextView 
        android:id="@+id/toastTextView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:paddingBottom="5dp"
        android:paddingTop="5dp"
        android:paddingLeft="15dp"
        android:fontFamily="@font/made_evolve_sans_light"
        android:textColor ="#424242"
        android:textSize="25sp"
    />
</LinearLayout>

And then for the custom toast I did:

        Toast toast = Toast.MakeText(Application.Context, message, ToastLength.Long);
        TextView v = (TextView)toast.View.FindViewById(Resource.Id.toastTextView);
        v.SetTextSize(Android.Util.ComplexUnitType.Sp, 25);
        toast.View.Background.SetColorFilter(Android.Graphics.Color.ParseColor("#F2e3dace"), PorterDuff.Mode.SrcIn);

        toast.SetGravity(GravityFlags.Center, 0, 0);
        toast.Show();

But then at runtime, the textview v is always null.

How do I find my textview with my custom font by its ID?

THank you!

Answer 1

as far as i know the textview id from toast is: android.R.id.message

Answer 2

From your description, you want to create Toast with custom font in Xamarin.forms, you can use DependencyService to get it.

In your Share code project, create interface toast:

public interface toast
{
    void Show(string message);
}

Then implement this interface in Android platform. you can use following code to create custom font Toast.Don't forget to register the platform implementations.

[assembly: Xamarin.Forms.Dependency(typeof(Toast_Android))]
namespace FormsSample.Droid
{
public class Toast_Android : toast
{
    public void Show(string message)
    {
        
        Toast toast = Toast.MakeText(Application.Context, message, ToastLength.Long);
        TextView v = (TextView)toast.View.FindViewById(Android.Resource.Id.Message);
        v.SetTextSize(Android.Util.ComplexUnitType.Sp, 25);
        toast.View.Background.SetColorFilter(Android.Graphics.Color.ParseColor("#F2e3dace"), PorterDuff.Mode.SrcIn);

        var typeface = Typeface.Create("customfont", Android.Graphics.TypefaceStyle.Bold);
        v.Typeface = typeface;

        toast.SetGravity(GravityFlags.Center, 0, 0);
        toast.Show();


    }
}
 }

For Android native platform, there is one textview from Toast: Android.Resource.Id.Message

Then you can get Toast by Button.click method:

private void btn2_Clicked(object sender, EventArgs e)
    {
        DependencyService.Get<toast>().Show("Toast Message");
    }

The screenshot: