ios – 具有自动布局的UILabel高度动画

概述我的观点和UIButton都有一个UILabel.当按钮触摸UILabel时应更改动画高度,取决于标签内容.我在尝试这个： - (void)viewDidLoad { self.textLabel= [[UILabel alloc] initWithFrame:CGRectZero]; self.textLabel.numberOfLines=0; 我的观点和UIbutton都有一个UILabel.当按钮触摸UILabel时应更改动画高度,取决于标签内容.我在尝试这个：

- (voID)vIEwDIDLoad {        self.textLabel= [[UILabel alloc] initWithFrame:CGRectZero];        self.textLabel.numberOflines=0;        self.textLabel.Font= [UIFont systemFontOfSize:14];        self.textLabel.backgroundcolor= [UIcolor lightGraycolor];        self.textLabel.text= @"short text";        [self.vIEw addSubvIEw:self.textLabel];        [self.textLabel setTranslatesautoresizingMaskIntoConstraints:NO];        [self.vIEw addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-10-[_textLabel]-10-|"        options:0        metrics:nil        vIEws:NSDictionaryOfVariableBindings(_textLabel)]];        self.button= [UIbutton buttonWithType:UIbuttonTypeSystem];        [self.button addTarget:self action:@selector(buttontouched:) forControlEvents:UIControlEventtouchUpInsIDe];        [self.button setTitle:@"Tap" forState:UIControlStatenormal];        self.button.backgroundcolor= [UIcolor greencolor];        [self.button setTranslatesautoresizingMaskIntoConstraints:NO];        [self.vIEw addSubvIEw:self.button];        [self.vIEw addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-10-[_button]-10-|"                                   options:0                                   metrics:nil                                   vIEws:NSDictionaryOfVariableBindings(_button)]];        [self.vIEw addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-50-[_textLabel(>=0)]-10-[_button(==20)]"                                   options:0                                   metrics:nil                                    vIEws:NSDictionaryOfVariableBindings(_textLabel,_button)]];}- (voID)buttontouched:(ID)buttontouched {        self.shortText =!self.shortText;        self.textLabel.text= self.shortText ?@"short text":@"long long long text\nlong long long text\nlong long long text\n";        [UIVIEw animateWithDuration:1.0                         animations:^{                             [self.vIEw layoutIfNeeded];                     }];}

解决方法 在动画块之前,您需要调用[self.vIEw setNeedsUpdateConstraints]以触发告诉视图在调用layoutIfNeeded时需要更新约束

所以新方法：

- (voID)buttontouched:(ID)buttontouched {    self.shortText =!self.shortText;    self.textLabel.text= self.shortText ?@"short text":@"long long long text\nlong long long text\nlong long long text\n";    [self.vIEw setNeedsUpdateConstraints];    [UIVIEw animateWithDuration:1.0                     animations:^{                         [self.vIEw layoutIfNeeded];    }];}

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