Could work

var buttonWindow;
var ctx = com.mojang.minecraftpe.MainActivity.currentMainActivity.get();

var BitmapFactory = android.graphics.BitmapFactory;
var BitmapDrawable = android.graphics.drawable.BitmapDrawable;

let imgSlot = new BitmapFactory.decodeFile("mnt/sdcard/download/Offhand/offhand.png");
let iconSlot = new BitmapDrawable(imgSlot);

const DENSITY = ctx.getResources().getDisplayMetrics().density;

function px2dip(px){
    return Math.floor(px / DENSITY);
}

function newLevel() {
    ctx.runOnUiThread(new java.lang.Runnable({
        run: function() {
            try {

                buttonWindow = new android.widget.PopupWindow();

                var layout = new android.widget.RelativeLayout(ctx);
                var button = new android.widget.Button(ctx);

                button.setText("Offhand");
                button.setOnClickListener(new android.view.View.OnClickListener({

                    onClick: function(viewarg) {
                        clientMessage("Block Placed");
                    }

                }));

                layout.addView(button);

                buttonWindow.setContentView(layout);
                buttonWindow.setWidth(110);
                buttonWindow.setHeight(110);
                buttonWindow.setBackgroundDrawable(iconSlot);
                buttonWindow.showAtLocation(ctx.getWindow().getDecorView(), android.view.Gravity.LEFT | android.view.Gravity.BOTTOM, 200, 0);

            } catch (problem) {
                print("Button could not be displayed: " + problem);
            }
        }
    }));
}

function leaveGame() {

    ctx.runOnUiThread(new java.lang.Runnable({
        run: function() {

            if (buttonWindow != null) {
                buttonWindow.dismiss();
                buttonwindow = null;
            }

        }
    }));

}