如何判断UILabel何时被截断和/或其换行符位置将会改变 [英] How to tell when a UILabel will be truncated an/or its line break position will change

问题描述

我有一个多行 UILabel （ numberOfLines = 0）。它的宽度可以在运行时改变，有时这导致截断和/或重新包装。一些示例最好地说明了这一点：

示例1：宽度减少导致不同的换行符

>

示例2：宽度减小导致截断

示例3：宽度减少导致截断和不同的换行符位置

示例4：宽度减少对截断或换行符位置没有任何影响

由于格式化的变化可能相当刺激，我打算掩盖它一些动画（可能是淡入/淡出）。但是，第一个障碍是确定何时我需要这样做。我不想在标签重新调整大小时应用动画 - 只有当它会导致截断或换行符位置发生更改时。

我如何测试这个？测试应该返回YES，例如1，2和3，但不是例如4.

注意：调整大小绝不会改变我的示例中的行数。

注意2：如果有人有更好的标签与文本格式相关，我很想知道他们 - 随时可以编辑。

注意3：如果你有兴趣看到这个行为完成，请在iPhone上尝试Apple的mail.app。查看收件箱时，滑动电子邮件，并在其重新换行和/或截断时（但不需要时）淡入/淡出汇总行。

解决方案

您可以知道显示特定 NSString 实例所需的标签大小。例如，你可以使用那个：

- （CGSize）sizeWithFont：（UIFont *）font constrainedToSize： （CGSize）size lineBreakMode：（UILineBreakMode）lineBreakMode

如果使用指定的约束来渲染字符串，则返回字符串的大小。

所以你想要的是获得 CGSize 特殊字符串并检查它是否不大于 UILabel size：

  UILabel * label; 
 CGSize sizeNeeded = [label.text sizeWithFont：label.font constrainedToSize：CGSizeMake（label.bounds.size.width，MAXFLOAT）]; 
 if（sizeNeeded.height> label.bounds.size.height）
 {
 NSLog（@String is truncated）; 
} 
  

更有用 NSString 方法，您可以在这里找到： NSString UIKit添加参考

好的，另一种方式来做你想做的事情：

1）创建2 UILabel 具有相同的属性，但第二个（ label2 ）将与另一个 c $ c>。

2）设置 alpha 属性 label2



3）当编辑模式开始时，这样的动画： <$ c> / p>



  // label1.alpha == 1.0，label2.alpha == 0.0 
 {[UIView animateWithDuration：0.5 animations： ^ {
 label1.alpha = 0.0; 
 label2.alpha = 1.0; 
}]; 
  

4）编辑模式结束时：

  {[UIView animateWithDuration：0.5 animations：^ {
 label1.alpha = 1.0; 
 label2.alpha = 0.0; 
}]; 
  

这将给出与Mail.app中相同的结果

I have a multi-line UILabel (numberOfLines = 0). It's width can change at runtime, and sometimes this leads to truncation and/or re-wrapping. Some examples illustrate this best:

Example 1: the reduction in width leads to a different line break point

Example 2: the reduction in width leads to truncation

Example 3: the reduction in width leads to both truncation and a different line break position

Example 4: the reduction in width does not have any effect on truncation or line break position

Since this change in formatting can be quite jarring, I intend to mask it behind some animation (probably a fade in/fade out). However, the first hurdle is identifying when I need to do this. I don't want to apply the animation whenever the label re-sizes - only when it will cause a change in either truncation or line break positions.

How might I test this? The test should return YES for example 1, 2, and 3, but NO for example 4.

Note: the resizing will never alter the number of lines in my example.

Note 2: if anyone has some better tags related to text formatting I'd love to know them - feel free to edit.

Note 3: if you are interested in seeing this behavior accomplished, try Apple's mail.app on the iPhone. When viewing the inbox, swipe an email and watch the summary line fade-in/out as it re-wraps and/or truncates (but not when it doesn't need to).

解决方案

You could know the size of label that is needed to display a particular NSString instance. For example, you could use that one:

- (CGSize)sizeWithFont:(UIFont *)font constrainedToSize:(CGSize)size lineBreakMode:(UILineBreakMode)lineBreakMode

Returns the size of the string if it were rendered with the specified constraints.

So what you want is to get CGSize for a particular string and check if it is not larger then UILabel size:

    UILabel *label;
    CGSize sizeNeeded = [label.text sizeWithFont:label.font constrainedToSize:CGSizeMake(label.bounds.size.width, MAXFLOAT)];
    if (sizeNeeded.height > label.bounds.size.height)
    {
        NSLog(@"String is truncated");
    }

More useful NSString methods you could find here: NSString UIKit Additions Reference

Ok, another way of doing what you want:

1) Create 2 UILabel with the same properties but second one (label2) will be with another one width.

2) Set alpha property of label2 to 0.0 in non-edit mode.

3) When edit mode begins make such animation:

// label1.alpha == 1.0, label2.alpha == 0.0 
{[UIView animateWithDuration:0.5 animations:^{
    label1.alpha = 0.0;
    label2.alpha = 1.0;
}];

4) When edit mode ends:

{[UIView animateWithDuration:0.5 animations:^{
    label1.alpha = 1.0;
    label2.alpha = 0.0;
}];

That will give you the same result as in Mail.app

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