I don’t use app inventor and it’s been a long time, but here is a solution using only java, in case someone still needs it.

public void createToast(AndroidViewComponent component,int gravity1,int gravity2){
   
    View content = component.getView();
    try{
        //declare content
        Toast toast = new Toast(context);
        LinearLayout toast_layout = new LinearLayout(context);
        TextView toast_msg = new TextView(context);
        //add rounded border to toast
        android.graphics.drawable.GradientDrawable toast_borders = new android.graphics.drawable.GradientDrawable();
        //background color of toast
        toast_borders.setColor(Color.parseColor("#434343"));
        //round size
        toast_borders.setCornerRadius(20);
        //add shadow
        toast_layout.setElevation(15);
        toast_layout.setBackground(toast_borders);

        //set layout type
        toast_layout.setLayoutParams(new LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
        toast_layout.setOrientation(LinearLayout.VERTICAL);

        //layout padding
        toast_layout.setPadding(15, 15, 16, 15);

        //text size
        toast_msg.setTextSize(15);
        //text padding
        toast_msg.setPadding(15, 15, 16, 15);
        //text color
        toast_msg.setTextColor(Color.parseColor("#ff0000"));
        //set text
        toast_msg.setText("Your Message!");

        //add your text to the toast layout
        toast_layout.addView(toast_msg);  
        //set the layout to your toast
        toast.setView(toast_layout);

        //set toast duration
        toast.setDuration(Toast.LENGTH_LONG);
        toast.setGravity(gravity1 | gravity2, 32, 32);
        toast.show();
        if(autoInvisible == true){
            content.setVisibility(View.GONE);}
    }catch (Exception e){e.printStackTrace();}
}

I am creating a extension for app inventor for custom toast in which I am only allowed to use java but in the android it can be done using Inflater. Is there any way to create custom toast with only Java.

Here is what I have did

public void createToast(AndroidViewComponent component,int gravity1,int gravity2){
toast = new Toast(context);
    View content = component.getView();
    try{
    toast.setView(content);
    toast.setDuration(Toast.LENGTH_LONG);
    toast.setGravity(gravity1 | gravity2, 32, 32);
    toast.show();
        if(autoInvisible == true){
            content.setVisibility(View.GONE);}
      }catch (Exception e){e.printStackTrace();}
  }