Resizing uiview from its corners

Question

How to resize the uiview using touches on the corners of the uiview. For e.g. it top left corner is touched and dragged upwards its y coordinate and height should increase, if bottom right corner is dragged then its origin should be same but height and width should be changed.

Answer 1

You can do it by changing the view.layer anchor point.

You can read about it here: Layer Geometry

To get the UIView corners you can use -

CGRect topLeftCorner = CGRectMake(CGRectGetMinX(self.view),CGRectGetMinY(self.view),20,20); //Will define the top-left corner of the view with 20 pixels inset. you can change the size as you wish.

CGRect topRightCorner  =  CGRectMake(CGRectGetMaxX(self.view),CGRectGetMinY(self.view),20,20); //Will define the top-right corner.

CGRect bottomRightCorner  =   CGRectMake(CGRectGetMinX(self.view),CGRectGetMaxY(self.view),20,20); //Will define the bottom-right corner.

CGRect bottomLeftCorner  = CGRectMake(CGRectGetMinX(self.view),CGRectGetMinY(self.view),20,20); //Will define the bottom-left corner.

Then You can cheek if the touch point is inside one of the corners. and set the layer.anchorPoint according.

  BOOL isBottomLeft =  CGRectContainsPoint(bottomLeftCorner, point);
  if(isLeft) view.layer.anchorPoint = CGPoint(0,0);
   //And so on for the others (off course you can optimize this code but I wanted to make the explanation simple).

Then when you will resize the view it will resize from the anchor point.

Good Luck

Answer 2

#define TOUCH_OFFSET 20 //distance from rectangle edge where it can be touched

UITouch* touch = [... current touch ...];

CGRect rectagle = [... our rectangle ... ];
CGPoint dragStart = [touch previousLocationInView:self.view];
CGPoint dragEnd = [touch locationInView:self.view];

//this branch is not necessary if we let users resize the rectangle when they tap its border from the outside
if (!CGRectContainsPoint(rectangle, dragStart)) {
  return;
}

if (abs(dragStart.x - CGRectGetMinX(rectangle)) < TOUCH_OFFSET) {
   //modify the rectangle appropiately, e.g.
   rectangle.origin.x += (dragEnd.x - dragStart.x);
   rectangle.size.width -= (dragEnd.x - dragStart.x);

   //TODO: you have to handle situation when width is zero or negative - flipping the rectangle or giving it a minimum width
}
else if (abs(dragStart.x - CGRectGetMaxX(rectangle)) < TOUCH_OFFSET) {
}

if (abs(dragStart.y - CGRectGetMinY(rectangle)) < TOUCH_OFFSET) {
}
else if (abs(dragStart.y - CGRectGetMaxY(rectangle)) < TOUCH_OFFSET) {
}