Android 安卓：我如何将它分为两类？

我在网上读了一篇关于画圆的教程（教程的第一部分）：

我成功了。现在我想将它们分为两类：

MainActivity.java

public class MainActivity extends AppCompatActivity {


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(new SimpleView(this));

    }

}

public class SimpleView extends SurfaceView {

public SimpleView(Context context) {

    super(context);
}

@Override
protected void onDraw(Canvas canvas) {

    super.onDraw(canvas);
    int x = getWidth();
    int y = getHeight();
    int radius;
    radius = 100;
    Paint paint = new Paint();
    paint.setStyle(Paint.Style.FILL);
    paint.setColor(Color.GREEN);
    canvas.drawPaint(paint);
    // Use Color.parseColor to define HTML colors
    paint.setColor(Color.parseColor("#CD5C5C"));
    canvas.drawCircle(x / 2, y / 2, radius, paint);

}

}

SimpleView.java

public class MainActivity extends AppCompatActivity {


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(new SimpleView(this));

    }

}

public class SimpleView extends SurfaceView {

public SimpleView(Context context) {

    super(context);
}

@Override
protected void onDraw(Canvas canvas) {

    super.onDraw(canvas);
    int x = getWidth();
    int y = getHeight();
    int radius;
    radius = 100;
    Paint paint = new Paint();
    paint.setStyle(Paint.Style.FILL);
    paint.setColor(Color.GREEN);
    canvas.drawPaint(paint);
    // Use Color.parseColor to define HTML colors
    paint.setColor(Color.parseColor("#CD5C5C"));
    canvas.drawCircle(x / 2, y / 2, radius, paint);

}

}

然而，我没能让他们工作：它从不画任何东西

---

我在这里做错了什么？

如果您想使用SurfaceView，您只需在构造函数上调用

setWillNotDraw（false）

，这样类就会如下所示：

public class SimpleView extends SurfaceView {

    public SimpleView(Context ctx) {
        super(ctx);
        setWillNotDraw(false); //notice this method call IMPORTANT
    }

    @Override
    protected void onDraw(Canvas canvas) {

        super.onDraw(canvas);
        int x = getWidth();
        int y = getHeight();
        int radius;
        radius = 100;
        Paint paint = new Paint();
        paint.setStyle(Paint.Style.FILL);
        paint.setColor(Color.GREEN);
        canvas.drawPaint(paint);
        // Use Color.parseColor to define HTML colors
        paint.setColor(Color.parseColor("#CD5C5C"));
        canvas.drawCircle(x / 2, y / 2, radius, paint);


    }
}

---

将

SurfaceView

更改为

View

@ssh为什么

SurfaceView扩展视图

@cricket_007是的，但绘图场景不同。@ssh如果您认为这是解决方案，您可以在回答中解释这一点。噢，在我将其更改为视图后，它会起作用，请问有什么区别？如果我想保持SurfaceView，我该怎么做？