ios：UIButton标题格式延迟

Question

我有一些按钮，我保持对齐并换行标题文字。

当我运行应用程序时，文本未格式化的时间会延迟：

pre-format text http://imageshack.us/a/img28/1958/preformat.jpg

当对齐和包装生效时：

post-format text http://imageshack.us/a/img821/6118/postformat.jpg

在模拟器上，延迟非常明显（约1秒），在我的队友的iPhone 5上，延迟要小得多，但仍然很明显。

导致这种延迟的原因是什么？我能解决这个延迟吗？

提前致谢！

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修改

在我的viewDidLoad方法中，我创建了10个按钮：

for (int i = 1; i <= STEP_NUMBER; ++i)
    [self createStepButtion:i isIphone:isIphone isRetina:isRetina];

在createStepButton中，相关代码如下：

UIButton * b = [UIButton buttonWithType:UIButtonTypeCustom];

// Listener
[b addTarget:self action:@selector(goToStep:) forControlEvents:UIControlEventTouchUpInside];

[self.scrollView addSubview:b];

// Set button size.
CGFloat width = self.scrollView.frame.size.width;
// CGRectMake(x, y, width, height)
int y = stepNum * margin + (stepNum - 1) * buttonHeight;
int buttonWidth = width - margin * 2;
b.frame = CGRectMake(margin, y, buttonWidth, buttonHeight);

b.layer.cornerRadius = cornerRadius;
b.clipsToBounds = YES;
b.showsTouchWhenHighlighted = YES;

// Image
[b setImage:img forState:UIControlStateNormal];
b.imageEdgeInsets = [self makeImageInsets:buttonWidth];

// Text
[b setTitleEdgeInsets:UIEdgeInsetsMake(0, titleLeftMargin, 0, titleRightMargin)];
b.contentHorizontalAlignment = UIControlContentHorizontalAlignmentLeft;
b.titleLabel.lineBreakMode = UILineBreakModeWordWrap;
[b setTitle:[NSString stringWithFormat:@"%i - %s", stepNum, STEP_NAMES[stepNum - 1]]forState:UIControlStateNormal];

[b setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
b.titleLabel.font = [UIFont systemFontOfSize:fontSize];

// Background
[b setBackgroundColor:[UIColor whiteColor]];

// The step number this button represents.
b.tag = stepNum;