Question

我的应用每分钟都会收到一次测量。当测量值为0时，我希望在中间显示标签。当它大于那个时，我希望标签消失。我遇到的问题是，一旦标签出现，一旦我将其隐藏模式设置为true，它就不会隐藏。

 UILabel *emptyBagLabel = [[UILabel alloc] init];
    emptyBagLabel.textAlignment = NSTextAlignmentCenter;
    emptyBagLabel.textColor = [UIColor darkGrayColor];
    emptyBagLabel.numberOfLines = 0;
    emptyBagLabel.text = @"EMPTY POUCH";
    emptyBagLabel.translatesAutoresizingMaskIntoConstraints = NO;
    emptyBagLabel.hidden = true;

    [self addSubview:emptyBagLabel];

    [emptyBagLabel.centerXAnchor constraintEqualToAnchor:self.centerXAnchor].active = YES;
    [emptyBagLabel.centerYAnchor constraintEqualToAnchor:self.centerYAnchor].active = YES;
    [emptyBagLabel.widthAnchor constraintEqualToAnchor:self.widthAnchor].active = YES;
    [emptyBagLabel.heightAnchor constraintEqualToConstant:100].active= YES;

    if (measurement == 0 || measurement <= 0.005) {
        emptyBagLabel.hidden = false;
    }

    if (measurement > 0.005) {
        emptyBagLabel.hidden = true;
    }

我一直在摸不着头脑，对我如何解决这样一个微不足道的问题感到有点沮丧。我每分钟都会调用它的方法。我知道方法和hidden = true行被调用，所以我不确定是什么导致了这个问题。

Answer 1

以编程方式添加的子视图应该是懒惰添加的，因此您只能获得一个子视图实例。我像这样重构代码......

- (UILabel *)emptyBagLabel {
    UILabel *emptyBagLabel = (UILabel *)[self.view viewWithTag:128];
    if (!emptyBagLabel) {
        emptyBagLabel = [[UILabel alloc] init];
        emptyBagLabel.tag = 128;

        // set all of the attributes her for how the label looks, textColor, etc.
        // everything except the properties that change over time

        [self addSubview:emptyBagLabel];
    }
    return emptyBagLabel;
}

// if this view is built using initWithFrame...
- (id)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        [self emptyBagLabel];  // to add the label initially
    }
    return self;
}

// if this view is ever loaded from a nib, then
- (id)initWithCoder:(NSCoder *)aDecoder {
    self = [super initWithCoder:aDecoder];
    if (self) {
        [self emptyBagLabel];
    }
    return self;

}

// elsewhere in the view, when you get the measurement
// side note: alpha is usually a better choice than hidden because you can animate it
if (measurement == 0 || measurement <= 0.005) {
    self.emptyBagLabel.alpha = 1.0;
}

if (measurement > 0.005) {
    self.emptyBagLabel.alpha = 0.0;
}

设置为隐藏时，UILabel不会隐藏

1 个答案: