iOS自动布局动画

Question

比如当我点击按钮的时候执行如下代码:

UIView *view = [[UIView alloc] init];
[self.view addSubview:view];
view.backgroundColor = [UIColor blackColor];
[view mas_makeConstraints:^(MASConstraintMaker *make) {
    make.leading.equalTo(@0);
    make.trailing.equalTo(@0);
    make.bottom.equalTo(@-100);
    make.height.equalTo(@320);
}];


[view mas_updateConstraints:^(MASConstraintMaker *make) {
    make.bottom.equalTo(@-200);
}];

[UIView animateWithDuration:0.3f animations:^{
    [self.view layoutIfNeeded];
}];

但是动画很奇怪，不是我想要的。如果你添加了一个没有立即执行动画的约束，比如这样:

UIView *view = [[UIView alloc] init];
[self.view addSubview:view];
view.backgroundColor = [UIColor blackColor];
[view mas_makeConstraints:^(MASConstraintMaker *make) {
    make.leading.equalTo(@0);
    make.trailing.equalTo(@0);
    make.bottom.equalTo(@-100);
    make.height.equalTo(@320);
}];


dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
    [view mas_updateConstraints:^(MASConstraintMaker *make) {
        make.bottom.equalTo(@-200);
    }];

    [UIView animateWithDuration:0.3f animations:^{
        [self.view layoutIfNeeded];
    }];

});

这时候动画就正常了。糟糕，差点忘了说，autolayout我用的是Masonry

Answer 1

您还需要调用 [self.view setNeedsLayout] 以便在调用 [self.view layoutIfNeeded] 之前丢弃当前 View 布局。