Ios UITableViewHeaderFooterView无法将背景颜色更改为clearColor

这是我的TableHeaderView类，它扩展了UITableViewHeaderFooterView。此类没有Nib文件，所有操作都是通过编程完成的

我希望它的背景色是透明的，但我不能让它工作。 我尝试过设置[self.backgroundView setBackgroundColor:[UIColor clearColor]]、[self-setBackgroundView:nil]、[self.contentView setBackgroundColor:[UIColor clearColor]]，但最终结果始终是黑色背景

我已经花了好几个小时在这上面了，我真的不知道如何解决这个问题。我需要做什么才能让它工作

#import "TableHeaderView.h"

@interface TableHeaderView ()

@property (strong, nonatomic) UIView *background;
@property (strong, nonatomic) UILabel *text;

@end

@implementation TableHeaderView

- (instancetype)initWithReuseIdentifier:(NSString *)reuseIdentifier {
  self = [super initWithReuseIdentifier:reuseIdentifier];

  if (self.contentView) {
    self.background = [UIView new];
    [self.background setBackgroundColor:[UIColor colorWithWhite:0.0f alpha:0.5f]];
    [self.background setTranslatesAutoresizingMaskIntoConstraints:NO];

    self.text = [UILabel new];
    [self.text setTranslatesAutoresizingMaskIntoConstraints:NO];
    [self.text setText:@"Label"];
    [self.text setFont:[UIFont fontWithName:@"HelveticaNeue" size:15.0f]];
    [self.text setTextColor:[UIColor whiteColor]];
    [self.text setBackgroundColor:[UIColor redColor]];

    [self.background addSubview:self.text];
    [self.contentView addSubview:self.background];

    [self.contentView setTranslatesAutoresizingMaskIntoConstraints:NO];

    [self.background addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-10-[L]-10-|"
                                                                            options:0
                                                                            metrics:nil
                                                                              views:@{@"L": self.text}]];

    [self.background addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|[L]|"
                                                                            options:0
                                                                            metrics:nil
                                                                              views:@{@"L": self.text}]];

    [self.contentView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-10-[V]-10-|"
                                                                             options:0
                                                                             metrics:nil
                                                                               views:@{@"V": self.background}]];

    [self.contentView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-10-[V]|"
                                                                             options:0
                                                                             metrics:nil
                                                                               views:@{@"V": self.background}]];

    [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|[contentView]|"
                                                                 options:0
                                                                 metrics:nil
                                                                   views:@{@"contentView" : self.contentView}]];

    [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|[contentView]|"
                                                                 options:0
                                                                 metrics:nil
                                                                   views:@{@"contentView" : self.contentView}]];

    [self setBackgroundView:[UIView new]];                          // I can't change this background color to
    [self.backgroundView setBackgroundColor:[UIColor whiteColor]];  // be transparent. It gets black instead.
  }

  return self;
}

@end

更新

我尝试使用Nib文件并使用此初始值设定项：

- (instancetype)initWithReuseIdentifier:(NSString *)reuseIdentifier {
  self = [super initWithReuseIdentifier:reuseIdentifier];                                                                       

  if (self) {
    [self.contentView addSubview:[[[NSBundle mainBundle] loadNibNamed:@"TableHeaderView" owner:self options:nil] firstObject]];
  }
  return self;
}

Nib文件与旧代码一样设置视图。但它仍然不起作用，我不能得到一个透明的背景

更新2

问题是我还重写了drawRect:，这样做会导致黑色背景。将其中的代码移动到另一个方法解决了这个问题