UIButton *button =[[UIButton alloc]initWithFrame:CGRectMake(100, 100, 200, 40)];
button.backgroundColor = [UIColor redColor];
[button setTitle:@"我是Chenhaijian\n 我要换行" forState:UIControlStateNormal];
button.titleLabel.lineBreakMode = 0;//这句话很重要,不加这句话加上换行符也没用
[self.view addSubview:button];

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[mButton.titleLabel setNumberOfLines:0];
[mButton.titleLabel setTextAlignment:NSTextAlignmentCenter];