Android-真实绘图和手指运动之间的距离

我是Android开发的新手，这里有一个问题，因为我还没有找到关于Stackoverflow的任何答案

我编写了一个简单的代码，让用户用一个手指在屏幕上绘制一个边界框（从左上角到右下角）

类DrawView如下所示：

public class DrawView extends View {
Paint paint = new Paint();

public DrawView(Context context) {
    super(context);
}
public Point startPoint = new Point();
public Point endPoint = new Point();

@Override
public void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    paint.setColor(Color.RED);
    paint.setStrokeWidth(3);
    paint.setStyle(Paint.Style.STROKE);
    canvas.drawRect(startPoint.x,startPoint.y,endPoint.x,endPoint.y,paint);
}}

public class MainActivity extends AppCompatActivity {

DrawView drawView;

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

    drawView = new DrawView(this);
    drawView.setBackgroundColor(Color.WHITE);
    drawView.startPoint.set(0,0);
    drawView.endPoint.set(0,0);
    setContentView(drawView);
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    int eventAction = event.getAction();

    // you may need the x/y location
    int x = (int)event.getX();
    int y = (int)event.getY();

    // put your code in here to handle the event
    switch (eventAction) {
        case MotionEvent.ACTION_DOWN:
            drawView.startPoint.set(x,y);
            break;
        case MotionEvent.ACTION_UP:
            drawView.endPoint.set(x,y);
            drawView.invalidate();
            break;
        case MotionEvent.ACTION_MOVE:
            drawView.endPoint.set(x,y);
            drawView.invalidate();
            break;
    }

    // tell the View that we handled the event
    return true;
}}

主要活动如下所示：

public class DrawView extends View {
Paint paint = new Paint();

public DrawView(Context context) {
    super(context);
}
public Point startPoint = new Point();
public Point endPoint = new Point();

@Override
public void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    paint.setColor(Color.RED);
    paint.setStrokeWidth(3);
    paint.setStyle(Paint.Style.STROKE);
    canvas.drawRect(startPoint.x,startPoint.y,endPoint.x,endPoint.y,paint);
}}

public class MainActivity extends AppCompatActivity {

DrawView drawView;

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

    drawView = new DrawView(this);
    drawView.setBackgroundColor(Color.WHITE);
    drawView.startPoint.set(0,0);
    drawView.endPoint.set(0,0);
    setContentView(drawView);
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    int eventAction = event.getAction();

    // you may need the x/y location
    int x = (int)event.getX();
    int y = (int)event.getY();

    // put your code in here to handle the event
    switch (eventAction) {
        case MotionEvent.ACTION_DOWN:
            drawView.startPoint.set(x,y);
            break;
        case MotionEvent.ACTION_UP:
            drawView.endPoint.set(x,y);
            drawView.invalidate();
            break;
        case MotionEvent.ACTION_MOVE:
            drawView.endPoint.set(x,y);
            drawView.invalidate();
            break;
    }

    // tell the View that we handled the event
    return true;
}}

结果是我的手指点和屏幕上的真实绘图点之间有一个很长的距离，如下所示：

public class DrawView extends View {
Paint paint = new Paint();

public DrawView(Context context) {
    super(context);
}
public Point startPoint = new Point();
public Point endPoint = new Point();

@Override
public void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    paint.setColor(Color.RED);
    paint.setStrokeWidth(3);
    paint.setStyle(Paint.Style.STROKE);
    canvas.drawRect(startPoint.x,startPoint.y,endPoint.x,endPoint.y,paint);
}}

public class MainActivity extends AppCompatActivity {

DrawView drawView;

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

    drawView = new DrawView(this);
    drawView.setBackgroundColor(Color.WHITE);
    drawView.startPoint.set(0,0);
    drawView.endPoint.set(0,0);
    setContentView(drawView);
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    int eventAction = event.getAction();

    // you may need the x/y location
    int x = (int)event.getX();
    int y = (int)event.getY();

    // put your code in here to handle the event
    switch (eventAction) {
        case MotionEvent.ACTION_DOWN:
            drawView.startPoint.set(x,y);
            break;
        case MotionEvent.ACTION_UP:
            drawView.endPoint.set(x,y);
            drawView.invalidate();
            break;
        case MotionEvent.ACTION_MOVE:
            drawView.endPoint.set(x,y);
            drawView.invalidate();
            break;
    }

    // tell the View that we handled the event
    return true;
}}

---

蓝色的线是我的手指，红色的边框是屏幕上的真实图形。有人知道原因吗？非常感谢

活动和子视图的坐标原点不相同。我做了一些更正：

   public class MainActivity extends AppCompatActivity implements View.OnTouchListener{

        DrawView drawView;         

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


            drawView = new DrawView(this);
            drawView.setBackgroundColor(Color.WHITE);
            drawView.startPoint.set(0, 0);
            drawView.endPoint.set(0, 0);
            setContentView(drawView);
            drawView.setOnTouchListener(this);
        }



        @Override
        public boolean onTouch(View view, MotionEvent motionEvent) {
            int eventAction = motionEvent.getAction();


            // you may need the x/y location
            int x = (int) motionEvent.getX();
            int y = (int) motionEvent.getY();

            // put your code in here to handle the event
            switch (eventAction) {
                case MotionEvent.ACTION_DOWN:
                    drawView.startPoint.set(x, y);
                    break;
                case MotionEvent.ACTION_UP:
                    drawView.endPoint.set(x, y);
                    drawView.invalidate();
                    break;
                case MotionEvent.ACTION_MOVE:
                    drawView.endPoint.set(x, y);
                    drawView.invalidate();
                    break;
            }

            // tell the View that we handled the event
            return true;
        }
    }

---

这是因为

视图

的坐标与

活动

的坐标不同。在

视图中处理触摸事件。也就是说，将
onTouchEvent（）
方法移动到您的
DrawView
。