java - 从另一个类访问时，Getter 函数不返回值

Question

我有一个类(class)如下:

public class Element extends Activity
{
public float mX;
    public float mY;
 public void animate(long elapsedTime) 
    {
        mX += mSpeedX * (elapsedTime / 20f);
        mY += mSpeedY * (elapsedTime / 20f);
        setmX(mX);
        setmY(mY);
        checkBorders();
    }
public void setmX(float mX) 
{
Log.i("this.mX","mY at setmX read is :"+this.mX );      **//Line 1**
        this.mX = mX;
    }
public float getmX() {
        Log.i("mX","mX in getmX read is :"+mX );    **//Line 2**
        return mX;
    }

    public void setmY(float mY) {

        this.mY = mY;
        Log.i("this.mY","mY at setmY read is :"+this.mY );  **//Line 3**
    }

    public float getmY() {
        Log.i("mY","mY in getY read is :"+mY );    **//Line 4**

        return mY;
    }
}

我还有一个类

public class Panel extends SurfaceView implements SurfaceHolder.Callback
{
int x = 100;
    int y = 0;
public float xval;
    public float yval; 
@Override
    public boolean onTouchEvent(MotionEvent event) 
    {
        Element element = new Element();
        float x = event.getX();
        float y = event.getY();
        Log.i("x","x in panel is :"+x);
        //toast tos = new toast();

        xval = element.getmX();
        Log.i("xval","xval in playactivity obtained is :"+xval );   **//Line 5**
        yval = element.getmY();
        Log.i("yval","yval in playactivity obtained is :"+xval );    **//Line 6**
return super.onTouchEvent(event);
}

第 2、4、5 和 6 行显示的值为零。我不想这么做。下面是 logcat 图像。

我在访问说明符中犯了错误吗？

Answer 1

• 您不应在另一个类中创建 Activity 类(在您的 Element 类中)的对象。请浏览Application fundamentals
• 虽然您在 Panel 类中创建 Element 类的对象，但您从未调用 setter 方法 setmX() 和 setmY() 来设置值。您直接调用 getter 方法，它会返回默认值。