iOS开发之图片查看器

可以学到UIButton，UIImageView，UILabel的代码创建。实现一个简单的点击按钮，切换图片的小程序。

知识点：

在getter方法中，不要使用self.imageList(会调用imageList的getter方法)，应该使用_imageList，否则会死循环

self.noLabel.textAlignment = NSTextAlignmentCenter; // 居中对齐
CGFloat imageY = CGRectGetMaxY(self.noLabel.frame) + 20;   // 取出noLabel的最大Y值，一定用frame，不能用bounds

plist资源的使用

NSString *path = [[NSBundle mainBundle] pathForResource:@"ImageList" ofType:@"plist"];
NSLog(@"%@", path);
// 需要完整的路径
_imageList = [NSArray arrayWithContentsOfFile:path];

在OC中

1.如果对象没有强引用，会被立即释放

2.默认的对象，都是强引用的。

__weak Person *p = [[Person alloc] init];// 声明一个弱引用对象

git: https://git.oschina.net/taylordavid/ImageSeeker.git

部分代码展示：

#import "ViewController.h"

@interface ViewController ()

@property (nonatomic, strong) UILabel *noLabel;         // 序号
@property (nonatomic, strong) UIImageView *iconImage;   // 图片
@property (nonatomic, strong) UILabel *descLabel;       // 描述
@property (nonatomic, strong) UIButton *leftButton;     // 上一张
@property (nonatomic, strong) UIButton *rightButton;    // 下一张

@property (nonatomic, assign) int index;                // 当前显示的照片索引

@property (nonatomic, strong) NSArray *imageList;       // 信息

@end

@implementation ViewController

#pragma mark - 懒加载
- (NSArray *)imageList {
    if (_imageList == nil) {
        
        NSString *path = [[NSBundle mainBundle] pathForResource:@"ImageList" ofType:@"plist"];
        NSLog(@"%@", path);
        // 需要完整的路径
        _imageList = [NSArray arrayWithContentsOfFile:path];
        NSLog(@"%@", _imageList);
    }
    
    return _imageList;
}

- (UILabel *)noLabel {
    if (_noLabel == nil) {
        _noLabel = [[UILabel alloc] initWithFrame:CGRectMake(0, 20, self.view.bounds.size.width, 40)];
        _noLabel.textAlignment = NSTextAlignmentCenter; // 居中对齐
        [self.view addSubview:_noLabel];
    }
    
    return _noLabel;
}

- (UIImageView *)iconImage {
    if (_iconImage == nil) {
        CGFloat imageWidth = 200;
        CGFloat imageHeight = 200;
        CGFloat imageX = (self.view.bounds.size.width - imageWidth) * 0.5;
        CGFloat imageY = CGRectGetMaxY(self.noLabel.frame) + 20;   // 取出noLabel的最大Y值，一定用frame，不能用bounds
        
        _iconImage = [[UIImageView alloc] initWithFrame:CGRectMake(imageX, imageY, imageWidth, imageHeight)];
        _iconImage.backgroundColor = [UIColor redColor];
        [self.view addSubview:_iconImage];
    }
    
    return _iconImage;
}

- (UILabel *)descLabel {
    if (_descLabel == nil) {
        CGFloat descY = CGRectGetMaxY(self.iconImage.frame);
        _descLabel = [[UILabel alloc] initWithFrame:CGRectMake(0, descY, self.view.bounds.size.width, 100)];
        _descLabel.textAlignment = NSTextAlignmentCenter;
        _descLabel.numberOfLines = 0; // 不限制行数，但是保证label有足够的空间，高度大于行所占的总高度就好s
        [self.view addSubview:_descLabel];
    }
    
    return _descLabel;
}

- (UIButton *)leftButton {
    if (_leftButton == nil) {
        _leftButton = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 40, 40)];
        CGFloat centerY = self.iconImage.center.y;
        CGFloat centerX = self.iconImage.frame.origin.x * 0.5;
        _leftButton.center = CGPointMake(centerX, centerY);
        [_leftButton setBackgroundImage:[UIImage imageNamed:@"left_normal"] forState:UIControlStateNormal];
        [_leftButton setBackgroundImage:[UIImage imageNamed:@"left_highlighted"] forState:UIControlStateHighlighted];
        [_leftButton addTarget:self action:@selector(clickButton:) forControlEvents:UIControlEventTouchUpInside]; // 在OC中，很多方法的第一个参数都是触发该方法的对象，这里是self
        _leftButton.tag = -1;   // 设置tag
        [self.view addSubview:_leftButton];
    }
    
    return _leftButton;
}

- (UIButton *)rightButton {
    if (_rightButton == nil) {
        _rightButton = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 40, 40)];
        _rightButton.center = CGPointMake(self.view.bounds.size.width - self.leftButton.center.x, self.leftButton.center.y);
        [_rightButton setBackgroundImage:[UIImage imageNamed:@"right_normal"] forState:UIControlStateNormal];
        [_rightButton setBackgroundImage:[UIImage imageNamed:@"right_highlighted"] forState:UIControlStateHighlighted];
        // 添加监听事件
        [_rightButton addTarget:self action:@selector(clickButton:) forControlEvents:UIControlEventTouchUpInside];
        _rightButton.tag = 1;
        [self.view addSubview:_rightButton];
    }
    
    return _rightButton;
}

// 视图加载完后执行该函数
- (void)viewDidLoad {
    [super viewDidLoad];
    
    [self showPhotoInfo];
}

/*
 显示图片
 */
- (void)showPhotoInfo {
    self.noLabel.text = [NSString stringWithFormat:@"%d/%d", self.index + 1, 5];    // 设置序号
    
    self.iconImage.image = [UIImage imageNamed:self.imageList[self.index][@"name"]];
    self.descLabel.text = self.imageList[self.index][@"desc"];
    
    // 控制按钮状态
    self.rightButton.enabled = (self.index != 4);
    self.leftButton.enabled = (self.index != 0);
}

- (void)clickButton:(UIButton *)button {
    // 根据按钮调整当前显示图片的索引
    self.index += button.tag; // 这里通过设置特殊的tag实现的，挺巧妙
    
    [self showPhotoInfo];
}

@end

效果展示：