Ios UIButton标题标签在按下时调整大小？

我试图根据按下的状态给UIButton（它是用大小调整图像创建的）一些文本。我看到的行为是，当我按下按钮时，按钮图像的宽度会改变（变宽）。我想要的是文本在我按下时发生变化，但按钮的宽度保持不变。我已经摆弄了许多UIButton选项，但运气不好。下面是我目前正在做的：（有趣的是，按钮宽度的变化量似乎与按钮框架的宽度相关（更大->更多变化）：

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我想说你在反对自动布局（我看到了类似的行为，有人在这里回答了我的问题：），但我不确定当你问这个问题时是否存在。

UIImage *normalButton = [UIImage imageNamed:@"ButtonSlice.png"];
UIImage *pressedButton = [UIImage imageNamed:@"ButtonPressedSlice.png"];
normalButton = [normalButton resizableImageWithCapInsets:UIEdgeInsetsMake(0, 2, 0, 2)];
pressedButton = [pressedButton resizableImageWithCapInsets:UIEdgeInsetsMake(0, 2, 0, 2)];

UIButton *myButton = [UIButton buttonWithType:UIButtonTypeCustom];
myButton.contentHorizontalAlignment = UIControlContentHorizontalAlignmentFill;
[myButton setImage:normalButton forState:UIControlStateNormal];
[myButton setImage:pressedButton forState:UIControlStateHighlighted];
[myButton addTarget:self action:@selector(pressed) forControlEvents:UIControlEventTouchUpInside];

myButton.titleLabel.font = [UIFont fontWithName:@"Helvetica" size:18.0];

[myButton setTitleColor:[UIColor colorWithWhite:0.1 alpha:1] forState:UIControlStateNormal];
[myButton setTitle:@"Highlighted" forState:UIControlStateHighlighted];
[myButton setTitle:@"Default" forState:UIControlStateNormal];
myButton.titleLabel.textAlignment = UITextAlignmentCenter;

//No effect?
myButton.adjustsImageWhenHighlighted = NO;

myButton.frame = CGRectMake(ceil(controllerFrame.size.width/2 - 100), 80, 200, 50);