iOS UIImageView的contentMode属性详解

首先来看一下UIImageView的contentMode可以设置的常量:

typedef NS_ENUM(NSInteger, UIViewContentMode) {
    UIViewContentModeScaleToFill,
    UIViewContentModeScaleAspectFit,      // contents scaled to fit with fixed aspect. remainder is transparent
    UIViewContentModeScaleAspectFill,     // contents scaled to fill with fixed aspect. some portion of content may be clipped.
    UIViewContentModeRedraw,              // redraw on bounds change (calls -setNeedsDisplay)
    UIViewContentModeCenter,              // contents remain same size. positioned adjusted.
    UIViewContentModeTop,
    UIViewContentModeBottom,
    UIViewContentModeLeft,
    UIViewContentModeRight,
    UIViewContentModeTopLeft,
    UIViewContentModeTopRight,
    UIViewContentModeBottomLeft,
    UIViewContentModeBottomRight,
};

凡是没有带scale的，当图片尺寸超过ImageView的尺寸时，只有部分显示在ImageView中；当ImageView的尺寸大于图片尺寸时，图片会按指定的位置显示图片。UIViewContentModeScaleToFill属性是缩放填充，可能会导致图片变形。UIViewContentModeScaleAspectFit属性是等比缩放把图片整体显示在ImageView中，所以可能会出现ImageView有空白部分。UIViewContentModeScaleAspectFill属性是等比缩放图片把整个ImageView填充满，所以可能会出现图片部分显示不出来。
以女神(丫丫)图片做示例

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图片尺寸大小为400px*404px

图片尺寸.png

显示图片的ImageView的尺寸设置为600px*720px
显示图片的代码如下

#import "ExampleViewController.h"

@interface ExampleViewController ()

@end

@implementation ExampleViewController

#pragma mark - life cycle
- (void)viewDidLoad
{
    [super viewDidLoad];
    self.title = @"ContentMode的样式";
    self.view.backgroundColor = [UIColor whiteColor];
    
    [self.view addSubview:self.myImgView];
    self.myImgView.frame = CGRectMake(([UIScreen mainScreen].bounds.size.width - 300) / 2.0, 100, 300, 360);
}

#pragma mark - getter and setter
- (UIImageView *)myImgView
{
    if (_myImgView == nil) {
        _myImgView = [[UIImageView alloc] init];
        _myImgView.backgroundColor = [UIColor blackColor];
        _myImgView.clipsToBounds = YES;
        _myImgView.image = [UIImage imageNamed:@"yayazuimei"];
    }
    
    return _myImgView;
}

@end

主界面如下

主界面.png

代码如下

#import "RootViewController.h"
#import "ExampleViewController.h"

static NSString *const kUITableViewCellIdentifier = @"kUITableViewCellIdentifier";

@interface RootViewController ()

/** UI */
@property (nonatomic, strong) UITableView *myTableView;

/** DATA */
@property (nonatomic, strong) NSMutableArray *dataArray;

@end

@implementation RootViewController

#pragma mark - life cycle
- (void)viewDidLoad
{
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor whiteColor];
    self.title = @"点滴86";
    
    [self.view addSubview:self.myTableView];
    self.myTableView.frame = self.view.frame;
}

#pragma mark - UITableViewDataSource method
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    NSInteger rowCount = 0;
    rowCount = [self.dataArray count];
    
    return rowCount;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:kUITableViewCellIdentifier];
    cell.selectionStyle = UITableViewCellSelectionStyleNone;
    cell.textLabel.text = [self.dataArray objectAtIndex:indexPath.row];
    
    return cell;
}

#pragma mark - UITableViewDelegate method
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
    CGFloat cellHeight = 44;
    
    return cellHeight;
}

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    ExampleViewController *exampleVC = [[ExampleViewController alloc] init];
    UIViewContentMode imageContentMode = UIViewContentModeScaleToFill;
    NSString *tempStr = [self.dataArray objectAtIndex:indexPath.row];
    if ([tempStr isEqualToString:@"UIViewContentModeScaleToFill"]) {
        imageContentMode = UIViewContentModeScaleToFill;
    } else if ([tempStr isEqualToString:@"UIViewContentModeScaleAspectFit"]) {
        imageContentMode = UIViewContentModeScaleAspectFit;
    } else if ([tempStr isEqualToString:@"UIViewContentModeScaleAspectFill"]) {
        imageContentMode = UIViewContentModeScaleAspectFill;
    } else if ([tempStr isEqualToString:@"UIViewContentModeCenter"]) {
        imageContentMode = UIViewContentModeCenter;
    } else if ([tempStr isEqualToString:@"UIViewContentModeTop"]) {
        imageContentMode = UIViewContentModeTop;
    } else if ([tempStr isEqualToString:@"UIViewContentModeBottom"]) {
        imageContentMode = UIViewContentModeBottom;
    } else if ([tempStr isEqualToString:@"UIViewContentModeLeft"]) {
        imageContentMode = UIViewContentModeLeft;
    } else if ([tempStr isEqualToString:@"UIViewContentModeRight"]) {
        imageContentMode = UIViewContentModeRight;
    } else if ([tempStr isEqualToString:@"UIViewContentModeTopLeft"]) {
        imageContentMode = UIViewContentModeTopLeft;
    } else if ([tempStr isEqualToString:@"UIViewContentModeTopRight"]) {
        imageContentMode = UIViewContentModeTopRight;
    } else if ([tempStr isEqualToString:@"UIViewContentModeBottomLeft"]) {
        imageContentMode = UIViewContentModeBottomLeft;
    } else if ([tempStr isEqualToString:@"UIViewContentModeBottomRight"]) {
        imageContentMode = UIViewContentModeBottomRight;
    }
    
    exampleVC.myImgView.contentMode = imageContentMode;
    [self.navigationController pushViewController:exampleVC animated:YES];
}

#pragma mark - getter and setter
- (UITableView *)myTableView
{
    if (_myTableView == nil) {
        _myTableView = [[UITableView alloc] initWithFrame:CGRectZero style:UITableViewStylePlain];
        [_myTableView registerClass:[UITableViewCell class] forCellReuseIdentifier:kUITableViewCellIdentifier];
        _myTableView.delegate = self;
        _myTableView.dataSource = self;
    }
    
    return _myTableView;
}

- (NSMutableArray *)dataArray
{
    if (_dataArray == nil) {
        _dataArray = [[NSMutableArray alloc] init];
        [_dataArray addObject:@"UIViewContentModeScaleToFill"];
        [_dataArray addObject:@"UIViewContentModeScaleAspectFit"];
        [_dataArray addObject:@"UIViewContentModeScaleAspectFill"];
        [_dataArray addObject:@"UIViewContentModeCenter"];
        [_dataArray addObject:@"UIViewContentModeTop"];
        [_dataArray addObject:@"UIViewContentModeBottom"];
        [_dataArray addObject:@"UIViewContentModeLeft"];
        [_dataArray addObject:@"UIViewContentModeRight"];
        [_dataArray addObject:@"UIViewContentModeTopLeft"];
        [_dataArray addObject:@"UIViewContentModeTopRight"];
        [_dataArray addObject:@"UIViewContentModeBottomLeft"];
        [_dataArray addObject:@"UIViewContentModeBottomRight"];
    }
    
    return _dataArray;
}

@end

点击某一个样式，会进入样式显示页面
UIViewContentModeScaleToFill 样式如下，仔细看会看出来图片有变形哦