IOS學習筆記41--圖片的縮放（一）

圖片的縮放
 一：Pinch手勢對圖片進行縮放。即用兩根手指往不同方向拖拉照片，照片會被縮小或放大。
我理解的原理：等比縮放

先看如下關鍵代碼：

1.初始化參數

- (void)viewDidLoad

{

    [superviewDidLoad];

   

   lastDistance = 0.0;

   imageStartHeight = self.scaleImage.frame.size.height;

   imageStartWidth = self.scaleImage.frame.size.width;

}

 

2.縮放操作

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{

   

   CGPoint point1; //Point

   CGPoint point2;

   

   CGFloat sub_x; //兩手指間的 X距離

   CGFloat sub_y;//兩手指間的 Y距離

   

   CGFloat currentDistance; //當前兩手機間的距離

   CGRect imageFrame; //獲得活動範圍的frame

   

   NSArray *touchArray = [[event allTouches]allObjects];

   

   if ([touchArray count] >= 2) {

       

        point1 = [[touchArrayobjectAtIndex:0]locationInView:self.view];

        point2 = [[touchArrayobjectAtIndex:1]locationInView:self.view];

       

        sub_x = point1.x-point2.x;

        sub_y = point1.y-point2.y;

       

        currentDistance =sqrtf(sub_x * sub_x + sub_y * sub_y);

       

           

       if (lastDistance >0)

        {

            imageFrame =self.scaleImage.frame;

           

           if (currentDistance > lastDistance +2)

            {

//                NSLog(@"放大");

                imageFrame.size.width +=10;

               if (imageFrame.size.width >1000)

                {

                    imageFrame.size.width =1000;

                }

               lastDistance = currentDistance;

            }

           

           if (currentDistance < lastDistance -2)

            {

//                NSLog(@"縮小");

                imageFrame.size.width -=10;

               if (imageFrame.size.width <50)

                {

                    imageFrame.size.width =50;

                }

               lastDistance = currentDistance;

            }

           NSLog(@"currentDistance :%f  lastDistance : %f",currentDistance,lastDistance);

           if (currentDistance == lastDistance) {

               

                imageFrame.size.height =imageStartHeight*imageFrame.size.width/imageStartWidth;

               

               float addwidth = imageFrame.size.width -self.scaleImage.frame.size.width;

               float addheight = imageFrame.size.height -self.scaleImage.frame.size.height;

               

self.scaleImage.frame =CGRectMake(imageFrame.origin.x - addwidth/2.0f, imageFrame.origin.y - addheight/2.0f, imageFrame.size.width, imageFrame.size.height);

            }

        }

       else{

           

           lastDistance = currentDistance;

        }

    }

}

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event{

   lastDistance = 0;

}

其實他的關鍵所在就在於：判斷兩手指間的距離，當大於一定的距離的時候就對圖片的frame進行等比縮放，以達到縮放的目的。

有其他見解的同學留言討論。