iOS开发之Quartz2D 六 绘制UIImageView

#import <UIKit/UIKit.h>

@interface XMGImageView : UIView

/** <#注释#> */
@property (nonatomic, strong) UIImage *image;

- (instancetype)initWithImage:(UIImage *)image;

@end

#import "XMGImageView.h"

@implementation XMGImageView

- (instancetype)initWithImage:(UIImage *)image {

    if (self = [super init]) {
        //确定当前ImageView的尺寸大小
        self.frame = CGRectMake(0, 0, image.size.width, image.size.height);
        _image = image;
    }
    return self;
}

-(void)setImage:(UIImage *)image {
    _image = image;
    //重绘
    [self setNeedsDisplay];
}

- (void)drawRect:(CGRect)rect {
    // Drawing code
    [self.image drawInRect:rect];

}

@end

#import "ViewController.h"
#import "XMGImageView.h"

@interface ViewController ()

/** <#注释#> */
@property (nonatomic, weak) UIImageView *imageV;
@property (nonatomic, weak)  XMGImageView *xmgImageV;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

//    UIImageView *imageV = [[UIImageView alloc] init];
//    imageV.frame  = CGRectMake(0, 0, 200, 200);
//    imageV.image = [UIImage imageNamed:@"CTO"];
//    self.imageV = imageV;
//    [self.view addSubview:imageV];

    //initWithImage创建的ImageView的大小跟原始图片一样大
//    UIImageView *imageV = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"CTO"]];
//    [self.view addSubview:imageV];

    XMGImageView *xmgImageV = [[XMGImageView alloc] initWithImage:[UIImage imageNamed:@"CTO"]];
    [self.view addSubview:xmgImageV];

//
//    XMGImageView *xmgImageV = [[XMGImageView alloc] init];
//    xmgImageV.frame  = CGRectMake(0, 0, 200, 200);
//    xmgImageV.image = [UIImage imageNamed:@"CTO"];
//    self.xmgImageV = xmgImageV;
//    [self.view addSubview:xmgImageV];

}

-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {

    //self.imageV.image = [UIImage imageNamed:@"汽水"];
    self.xmgImageV.image = [UIImage imageNamed:@"汽水"];

}

@end

整体思路:

我们想要模仿系统的UIImageView,我们必须得要知道系统的UIView怎么用.

系统的用法是创建一个UIImageView对象,设置frame,给它传递一个UIImage,再把它添加到一个View上面就可以了.

可以切换图片.

这是第一个用法.

第二种用法,就是在创建的时候直接传递一个UIImage对象,使用initWithImage的方法进行创建一个UImageView的方式

用这种做法创建出来的UIImageView它的尺寸大小和原始图片的尺寸大小一样大.

所以我们自己的UIImageView也要具有这些功能.

实现步骤:

第一步:新建一个UIView,起名XMGImageView.

第二步:给XMGImageView添加一个UIImage属性,供外界传递图片

第三步:在DrawRect方法当中把传递的图片绘制到View上面

绘制方法为:[_image drawInRect:rect],绘制的图片尺寸大小和UIView的尺寸大小一样大.

第四步:重写UIImage属性的set方法,在set方法当中让View重新绘制.目的为了能够办到切换图片.

第五步:提供一个- (instancetype)initWithImage:(UIImage *)image方法.

在这个方法当中重写init方法

在初始化时,让View尺寸和图片的实际大小一样大.

然后再给UIImage属性赋值.

这样在绘制图片的时候,显示出来的View已经有尺寸了, 尺寸大小和图片的实际大小一样大.

具体代码实现:

- (instancetype)initWithImage:(UIImage *)image{

if (self = [super init]) {

self.frame = CGRectMake(0, 0, image.size.width, image.size.height);

_image = image;

}

return self;

}

-(void)setImage:(UIImage *)image{

_image = image;

[self setNeedsDisplay];

}

- (void)drawRect:(CGRect)rect {

[_image drawInRect:rect];

}