为什么 UITextField 上的 valueForKey: 会引发 UITextInputTraits 属性异常？

发布于 2024-11-18 21:32:51 字数 823 浏览 3 评论 0原文

运行此：

@try
{
    NSLog(@"1. autocapitalizationType = %d", [self.textField autocapitalizationType]);
    NSLog(@"2. autocapitalizationType = %@", [self.textField valueForKey:@"autocapitalizationType"]);
}
@catch (NSException *exception)
{
    NSLog(@"3. %@", exception);
}

输出此：

1. autocapitalizationType = 0
3. [<UITextField 0x6c15df0> valueForUndefinedKey:]: this class is not key value coding-compliant for the key autocapitalizationType.

我期望：

1. autocapitalizationType = 0
2. autocapitalizationType = 0

此异常仅发生在属于 UITextInputTraits 协议的属性上。 UITextField 的常规属性（例如具有 clearButtonMode）可以通过 valueForKey: 访问。

那么为什么不能使用键值编码访问 UITextInputTraits 属性呢？

原文

Running this:

@try
{
    NSLog(@"1. autocapitalizationType = %d", [self.textField autocapitalizationType]);
    NSLog(@"2. autocapitalizationType = %@", [self.textField valueForKey:@"autocapitalizationType"]);
}
@catch (NSException *exception)
{
    NSLog(@"3. %@", exception);
}

Outputs this:

1. autocapitalizationType = 0
3. [<UITextField 0x6c15df0> valueForUndefinedKey:]: this class is not key value coding-compliant for the key autocapitalizationType.

I was expecting:

1. autocapitalizationType = 0
2. autocapitalizationType = 0

This exception only happens with properties that are part of the UITextInputTraits protocol. Regular properties of a UITextField such has clearButtonMode can be accessed through valueForKey:.

So why can't you access UITextInputTraits properties with key-value coding?

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帅气称霸 2024-11-25 21:32:51

如果您深入研究 UIKit 框架并打开 UITextField.h，您会发现：

@interface UITextField : UIControl <UITextInput, NSCoding> {
  @private

    UITextInputTraits  *_traits;
    UITextInputTraits  *_nonAtomTraits;

您还会发现 clearButtonMode 被声明为 @property< /code> 在 UITextField 头文件中，但 autocapitalizationType （以及 UITextInputTraits 协议的其余部分）不是。

你和我都看不到 UITextField.m，所以我们真正能得出的结论是 Apple 实现了 UITextField 的 UITextInputTraits 协议在某种程度上不符合 KVC 标准。据推测，某处的粘合代码会将 [myTextField autocapitalizationType] 转换为适当的值，但无论发生什么幕后魔法，都会停止 valueForKey:。

If you delve into the UIKit framework and open up UITextField.h, you'll find:

@interface UITextField : UIControl <UITextInput, NSCoding> {
  @private

    UITextInputTraits  *_traits;
    UITextInputTraits  *_nonAtomTraits;

You'll also find that clearButtonMode is declared as a @property in the UITextField header file, but that autocapitalizationType (and the rest of the UITextInputTraits protocol) are not.

You and I don't get to see UITextField.m, so all we can really conclude is that Apple implemented the UITextField's UITextInputTraits protocol in a way that's not KVC compliant. Presumably glue code somewhere converts [myTextField autocapitalizationType] into the appropriate value, but whatever behind-the-scenes magic is taking place stops short of valueForKey:.

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