我是Android新手，我试图掌握多点触控输入。我开始使用一个简单的应用程序，允许用户通过用一根手指拖动和释放来创建Canvas上的矩形，我已经工作了。为了扩展它，我现在希望用户能够使用第二个手指旋转他们正在绘制的矩形，这是我的问题开始的地方。如图所示，添加第二个手指将导致多个矩形旋转，而不仅仅是当前的矩形，但是一旦释放第二个手指，它们将恢复到默认方向。
我已经在这里工作了一段时间，我认为我的核心问题是我错误地处理了两个（或多个手指）附带的多个MotionEvent。我留下的记录语句显示屏幕上的坐标，每个事件都与第一根手指触摸屏幕相关联，而不是切换到第二根手指。我尝试了多种访问和更改事件指针ID的配置，但仍然没有运气。如果有人能够在正确的方向上提供一些指导，我将非常感激。
我的代码如下：
public class BoxDrawingView extends View {
private static final String TAG = "BoxDrawingView";
private static final int INVALID_POINTER_ID = -1;
private int mActivePointerId = INVALID_POINTER_ID;
private Box mCurrentBox;
private List<Box> mBoxen = new ArrayList<>();
private Float mLastTouchX;
private Float mLastTouchY;
...
@Override
public boolean onTouchEvent(MotionEvent event) {
switch(MotionEventCompat.getActionMasked(event)) {
case MotionEvent.ACTION_DOWN:
mActivePointerId = MotionEventCompat.getPointerId(event, 0);
current = new PointF(MotionEventCompat.getX(event, mActivePointerId),
MotionEventCompat.getY(event, mActivePointerId));
action = "ACTION_DOWN";
// Reset drawing state
mCurrentBox = new Box(current);
mBoxen.add(mCurrentBox);
mLastTouchX = MotionEventCompat.getX(event, MotionEventCompat.getPointerId(event, 0));
mLastTouchY = MotionEventCompat.getY(event, MotionEventCompat.getPointerId(event, 0));
break;
case MotionEvent.ACTION_POINTER_DOWN:
action = "ACTION_POINTER_DOWN";
mActivePointerId = MotionEventCompat.getPointerId(event, 0);
mLastTouchX = MotionEventCompat.getX(event, MotionEventCompat.getPointerId(event, 0));
mLastTouchY = MotionEventCompat.getY(event, MotionEventCompat.getPointerId(event, 0));
break;
case MotionEvent.ACTION_MOVE:
action = "ACTION_MOVE";
current = new PointF(MotionEventCompat.getX(event, mActivePointerId),
MotionEventCompat.getY(event, mActivePointerId));
if (mCurrentBox != null) {
mCurrentBox.setCurrent(current);
invalidate();
}
if(MotionEventCompat.getPointerCount(event) > 1) {
int pointerIndex = MotionEventCompat.findPointerIndex(event, mActivePointerId);
float currX = MotionEventCompat.getX(event, pointerIndex);
float currY = MotionEventCompat.getY(event, pointerIndex);
if(mLastTouchX < currX) {
// simplified: only use x coordinates for rotation for now.
// +X for clockwise, -X for counter clockwise
Log.d(TAG, "Clockwise");
mRotationAngle = 30;
}
else if (mLastTouchX > getX()) {
Log.d(TAG, "Counter clockwise");
mRotationAngle = -30;
}
}
break;
case MotionEvent.ACTION_UP:
action = "ACTION_UP";
mCurrentBox = null;
mLastTouchX = null;
mLastTouchY = null;
mActivePointerId = INVALID_POINTER_ID;
break;
case MotionEvent.ACTION_POINTER_UP:
action = "ACTION_POINTER_UP";
int pointerIndex = event.getActionIndex();
int pointerId = event.getPointerId(pointerIndex);
if(pointerId == mActivePointerId){
mActivePointerId = INVALID_POINTER_ID;
}
break;
case MotionEvent.ACTION_CANCEL:
action = "ACTION_CANCEL";
mCurrentBox = null;
mActivePointerId = INVALID_POINTER_ID;
break;
}
return true;
}
@Override
protected void onDraw(Canvas canvas){
// Fill the background
canvas.drawPaint(mBackgroundPaint);
for(Box box : mBoxen) {
// Box is a custom object. Origin is the origin point,
// Current is the point of the opposite diagonal corner
float left = Math.min(box.getOrigin().x, box.getCurrent().x);
float right = Math.max(box.getOrigin().x, box.getCurrent().x);
float top = Math.min(box.getOrigin().y, box.getCurrent().y);
float bottom = Math.max(box.getOrigin().y, box.getCurrent().y);
if(mRotationAngle != 0) {
canvas.save();
canvas.rotate(mRotationAngle);
canvas.drawRect(left, top, right, bottom, mBoxPaint);
canvas.rotate(-mRotationAngle);
canvas.restore();
mRotationAngle = 0;
} else {
canvas.drawRect(left, top, right, bottom, mBoxPaint);
}
}
}
}
答案 0 :(得分：0)
有几种方法可以绘制东西，不仅在android中，而且在Java中。问题是你试图通过旋转画布来绘制矩形。这是一种方式，但根据我的个人经验，我认为如果你想旋转整个画面，这只是一个很好的选择。如果没有，那可能会有点棘手，因为你需要放置一个旋转轴，这似乎你没有使用，所以Android会假设你想要从左上角或视图中心旋转（我不＆＃ 39;记住）。
如果您选择了这个选择，您可以尝试这样做：
Matrix matrix = new Matrix();
matrix.setRotate(angle, rectangleCenterX, rectangleCenterY);
canvas.setMatrix(matrix);
但我建议你尝试不同的方法。通过计算多边形的轴，直接在要移动的矩形上进行旋转。您可以使用Java Math操作执行此操作：
public void formShape(int cx[], int cy[], double scale) {
double xGap = (width / 2) * Math.cos(angle) * scale;
double yGap = (width / 2) * Math.sin(angle) * scale;
cx[0] = (int) (x * scale + xGap);
cy[0] = (int) (y * scale + yGap);
cx[1] = (int) (x * scale - xGap);
cy[1] = (int) (y * scale - yGap);
cx[2] = (int) (x * scale - xGap - length * Math.cos(radians) * scale);
cy[2] = (int) (y * scale - yGap - length * Math.sin(radians) * scale);
cx[3] = (int) (x * scale + xGap - length * Math.cos(radians) * scale);
cy[3] = (int) (y * scale + yGap - length * Math.sin(radians) * scale);
}
所以（x，y）是你的矩形的中心，高度告诉你它有多大。在formShape(int[], int[], double)方法中，cx和cy将用于绘制您的形状，如果您想稍后放大或缩小，则使用缩放比例，如果不是仅使用scale = 1;
现在绘制矩形，你就是这样做的：
Paint paint = new Paint();
paint.setColor(Color.GRAY);
paint.setStyle(Style.FILL);
int[] cx = new int[4];
int[] cy = new int[4];
Box box = yourBoxHere;
box.formShape(cx, cy, 1);
Path path = new Path();
path.reset(); // only needed when reusing this path for a new build
path.moveTo(cx[0], cy[0]); // used for first point
path.lineTo(cx[1], cy[1]);
path.lineTo(cx[2], cy[2]);
path.lineTo(cx[3], cy[3]);
path.lineTo(cx[0], cy[0]); // repeat the first point
canvas.drawPath(wallpath, paint);
对于多点触控旋转侦听器，您应该在Activity或View中覆盖2个方法：
@Override
public boolean onTouch(View v, MotionEvent event) {
if(event.getId() == MotionEvent.ACTION_UP)
this.points = null;
}
}
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
if(event.getPointerCount() >= 2) {
float newPoints[][] = new float[][] {
{event.getX(0), event.getY(0)},
{event.getX(1), event.getY(1)}
};
double angle = angleBetweenTwoPoints(newPoints[0][0], newPoints[0][1], newPoints[1][0], newPoints[1][1]);
if(points != null) {
double difference = angle - initialAngle;
if(Math.abs(difference) > rotationSensibility) {
listener.onGestureListener(GestureListener.ROTATION, Math.toDegrees(difference));
this.initialAngle = angle;
}
} else {
this.initialAngle = angle;
}
this.points = newPoints;
}
}
public static double angleBetweenTwoPoints(double xHead, double yHead, double xTail, double yTail) {
if(xHead == xTail) {
if(yHead > yTail)
return Math.PI/2;
else
return (Math.PI*3)/2;
} else if(yHead == yTail) {
if(xHead > xTail)
return 0;
else
return Math.PI;
} else if(xHead > xTail) {
if(yHead > yTail)
return Math.atan((yHead-yTail)/(xHead-xTail));
else
return Math.PI*2 - Math.atan((yTail-yHead)/(xHead-xTail));
} else {
if(yHead > yTail)
return Math.PI - Math.atan((yHead-yTail)/(xTail-xHead));
else
return Math.PI + Math.atan((yTail-yHead)/(xTail-xHead));
}
}
很抱歉，但是这个答案很长，如果您对这些操作有任何疑问，并且想要更改解决方案的方法，请再次询问并在评论中告诉我。
我希望这很有帮助。