IOS学习笔记41--图片的缩放（一）

图片的缩放

一：Pinch手势对图片进行缩放。即用两根手指往不同方向拖拉照片，照片会被缩小或放大。

我理解的原理：等比缩放

先看如下关键代码：

1.初始化参数

- (void)viewDidLoad

{

[superviewDidLoad];

lastDistance = 0.0;

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

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

}

2.缩放操作

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

CGPoint point1; //Point

CGPoint point2;

CGFloat sub_x; //两手指间的 X距离

CGFloat sub_y;//两手指间的 Y距离

CGFloat currentDistance; //当前两手机间的距离

CGRect imageFrame; //获得活动范围的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(@"缩小");

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;

}

其实他的关键所在就在于：判断两手指间的距离，当大于一定的距离的时候就对图片的frame进行等比缩放，以达到缩放的目的。

有其他见解的同学留言讨论。