animateWithDuration无效

需要在后面增加一句

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[self.view layoutIfNeeded];

比如

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 __weak typeof(self) weakSelf = self;

[UIView animateWithDuration:0.2 animations:^{

weakSelf.progressLineWidth.constant=WIDTH;

[weakSelf.view layoutIfNeeded];

} completion:^(BOOL finished) {

weakSelf.progressLine.hidden=YES;

weakSelf.progressLineWidth.constant=0;

}];