问在API级别28中找不到画布变量

EN

canvas.saveLayer(0, 0, getWidth(), getHeight(), null,
                Canvas.MATRIX_SAVE_FLAG |
                        Canvas.CLIP_SAVE_FLAG |
                        Canvas.HAS_ALPHA_LAYER_SAVE_FLAG |
                        Canvas.FULL_COLOR_LAYER_SAVE_FLAG |
                        Canvas.CLIP_TO_LAYER_SAVE_FLAG);