隐藏/显示界面动画效果

之前用XXView.hidden = YES/NO去控制，怎样都没有出现过渡效果。

    [UIView animateWithDuration:0.4 animations:^{
        if (_summaryView.hidden) {
            _summaryView.hidden = NO;
            _summaryDetailTable.hidden = YES;
        }else{
            _summaryView.hidden = YES;
            _summaryDetailTable.hidden = NO;
        }
        
    } completion:^(BOOL finished) {
    }];
    
    [_buttonDetailSummary setTitle:(_summaryView.hidden @"Detail":@"Summary") forState:UIControlStateNormal];

后来改成用透明度去控制就搞定了，，

    [UIView animateWithDuration:0.4 animations:^{
        if (_summaryView.hidden) {
            _summaryDetailTable.alpha = 0.0;
            _summaryView.alpha = 1.0;
        }else{
            _summaryDetailTable.alpha = 1.0;
            _summaryView.alpha = 0.0;
        }
        
    } completion:^(BOOL finished) {
         _summaryView.hidden = !_summaryView.hidden;
        _summaryDetailTable.hidden = !_summaryDetailTable.hidden;
    }];
    
    [_buttonDetailSummary setTitle:(_summaryView.hidden @"Detail":@"Summary") forState:UIControlStateNormal];