iOS之让UISearchBar搜索图标和placeholder靠左显示

@interface ViewController () <UISearchBarDelegate>

/** xib搜索框 */
@property (weak, nonatomic) IBOutlet UISearchBar *searchBar;
/** 搜索图片(放大镜) */
@property (nonatomic, weak) UIImageView *imgV;
@end
@implementation ViewController

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
    // 查找放大镜图片ImageView
    for (UIImageView *imgV in _searchBar.subviews.firstObject.subviews.lastObject.subviews) {
        if ([imgV isMemberOfClass:[UIImageView class]]) {
            imgV.frame = CGRectMake(8, 7.5, 13, 13);
            _imgV = imgV;
            [_imgV addObserver:self forKeyPath:@"frame" options:NSKeyValueObservingOptionNew context:nil];
        }
    }
    // 设置searchBar文本颜色
    [self updateSeachBar];
}
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context
{
    // 修改放大镜Frame前, 移除观察者
    [_imgV removeObserver:self forKeyPath:@"frame"];
    // 修改Frame
    _imgV.frame = CGRectMake(8, 7.5, 13, 13);
    // 再次添加观察者
    [_imgV addObserver:self forKeyPath:@"frame" options:NSKeyValueObservingOptionNew context:nil];
}
#pragma mark -UISearchBarDelegate代理方法
- (void)searchBarTextDidBeginEditing:(UISearchBar *)searchBar
{
    if ([searchBar.text isEqualToString:searchBar.placeholder]) {
        // 无文本时, 显示placeholder
        searchBar.text = @"";
    }
    // 获取到UISearchBar中UITextField
    UITextField *searchField = [searchBar valueForKey:@"_searchField"];
    // 开始编辑要修改textColor颜色
    searchField.textColor = [UIColor blackColor];
    searchField.clearButtonMode = UITextFieldViewModeWhileEditing;
}
- (void)searchBarTextDidEndEditing:(UISearchBar *)searchBar
{
    [self updateSeachBar];
}
#pragma mark -根据文本内容设置searchBar颜色及clearButtonMode
- (void)updateSeachBar
{
    if ([_searchBar.text isEqualToString:@""]) {// 文本内容为空时
        UITextField *searchField = [_searchBar valueForKey:@"_searchField"];
        // 修改textColor为placeholderColor
        searchField.textColor = [searchField valueForKeyPath:@"_placeholderLabel.textColor"];
        searchField.text = searchField.placeholder;
        // 去除右侧clearButton
        searchField.clearButtonMode = UITextFieldViewModeNever;
    }
}
- (void)dealloc
{
    // 移除观察者
    [_searchBar removeObserver:self forKeyPath:@"frame"];
}