UIButton＆＃34; setAttributedTitle＆＃34;显示＆＃34;（null）＆＃34;

Question

按钮显示＆＃34;（null）＆＃34;如果使用＆＃34; setAttributedTitle＆＃34;。如果使用＆＃34; setTitle＆＃34;。

，它可以显示没有属性的正确字符串

知道如何正确显示属性吗？为什么它可以＆＃34; null＆＃34;？

// Set current bar button attributes
NSMutableAttributedString *currentBarAttributedString = [[NSMutableAttributedString alloc] init];
[currentBarAttributedString appendAttributedString:[[NSAttributedString alloc] initWithString:@"REQUEST\n"
                                                                         attributes:@{NSUnderlineStyleAttributeName: @(NSUnderlineStyleNone)}]];
[currentBarAttributedString appendAttributedString:[[NSAttributedString alloc] initWithString:@"EQUIPMENT"
                                                                         attributes:@{NSUnderlineStyleAttributeName: @(NSUnderlineStyleSingle)}]];
// Initialize buttons and set titles
UIButton *button1 = [UIButton buttonWithType:UIButtonTypeCustom];
[button1 setAttributedTitle:currentBarAttributedString forState:UIControlStateNormal];