在不同的类中使用Android canvas，调试崩溃错误

刚开始使用 Android、canvas 和作品。我有可以在图形对象上绘制形状的现有 Java 代码。我正在尝试在带有 Canvas 的 Android 应用程序中使用该代码。基本上，我试图避免重构我的所有 Java 代码以显式使用 Canvas。所以我正在制作我自己的“图形”对象。它应该做的就是调用适当的 Canvas 方法来绘制指定的形状。

我在这里阅读了多篇关于无法在onDraw()方法之外使用画布对象的帖子。据我了解，您不能将画布对象传递给不同的类并期望它正常工作。但我也没有完全理解这一切是如何运作的。

应用程序在 drawOval 方法的 Graphics 类中崩溃。我已经阅读了关于所有这些的日志，但我还没有找到一个很好的答案来说明为什么这特别不起作用。我一直无法找到一种以 Java 友好的方式（又名堆栈跟踪）获取崩溃日志的方法。它只是抛出Fatal signal 11 (SIGSEGV), code 1, fault addr 0x130 in tid 1520.

谢谢！如果需要更多详细信息，请告诉我。这是我的代码：

MainActivity

public class MainActivity extends AppCompatActivity {

    MyCanvas canvas;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        canvas = new MyCanvas(this);
        setContentView(canvas);
    }
}

MyCanvas View

public class MyCanvas extends View {
    Graphics graphics;
    List<Shape> shapes;

    public MyCanvas(Context context) {
        super(context);
        graphics = new Graphics();
        shapes = new ArrayList<>();
    }

    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        graphics.setCanvas(canvas); //Sets the canvas object in the graphics class
        for (Shape shape : shapes) {
            try { //this is in a try/catch block for custom exception handling
                //This just calls the specific shapes render method,
                //in this case, a circle from the makeShape Method
                //The graphics object then calls the specific shape to
                //render on the canvas
                shape.render(graphics, 0, 0); 
            } catch (ShapeException e) {
                e.printStackTrace();
            }
        }
        invalidate();
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                int x = (int) event.getX();
                int y = (int) event.getY();
                try { //this is in a try/catch block for custom exception handling
                    makeShape(x, y);
                } catch (ShapeException e) {
                    e.printStackTrace();
                }
                invalidate();

            case MotionEvent.ACTION_MOVE:
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL: {
                break;
            }
        }
        invalidate();
        return true;
    }

    public void makeShape(int x, int y) throws ShapeException{
        Point p = new Point(x, y);
        Shape shape = new Circle(p, 50, 50);
        shapes.add(shape);
    }

}

Graphics

public class Graphics {
    private Canvas canvas = null;

    public Graphics() {
    }

    public void setCanvas(Canvas canvas) {
        if (this.canvas == null) {
            this.canvas = canvas;
        }
    }

    public void drawOval(int x, int y, int width, int height) {
        Paint paint1 = new Paint();
        paint.setColor(Color.BLACK);
        canvas.drawCircle(500, 500, 50, paint1); //App crashes here
    }
}