ios iphone UILabel 多行文字自动换行 （自动折行）

【UILabel 自动换行】：

UIView *footerView = [[UIView alloc] initWithFrame:CGRectMake(10, 100, 300, 180)];
    UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(10, 100, 300, 150)];
    label.text = @"where are you? where are you? where are you? where are you? where are you? where are you? where are you? where are you? where are you? where are you?";
    //清空背景颜色
    label.backgroundColor = [UIColor clearColor];
    //设置字体颜色为白色
    label.textColor = [UIColor whiteColor];
    //文字居中显示
    label.textAlignment = UITextAlignmentCenter;
    //自动折行设置
    label.lineBreakMode = UILineBreakModeWordWrap;
    label.numberOfLines = 0;