ios - 在 Objective-C 中使用 KVC 读取联合属性
<p><p><strong>更新:</strong></p>
<p>我将问题归结为根本无法在下面看到的类上使用键值编码</p>
<pre><code>#import <Foundation/Foundation.h>
#import <GLKit/GLKit.h>
@interface CMTransformation : NSObject
@property(nonatomic) GLKVector3 position;
@property(nonatomic) GLKVector3 scale;
@property(nonatomic) GLKVector3 rotation;
@property(nonatomic) GLKVector3 anchor;
@property(nonatomic) GLKMatrix4 matrix;
- (GLKMatrix4)calculateMatrixWithParentTransformation:(CMTransformation *)parentTransformation;
@end
</code></pre>
<p>根据我的理解和经验，我应该能够将非 NSObject 作为 NSValue 提取出来，但是，我发现使用 KVC 语法无法访问这些项目(定义为联合):</p>
<pre><code>CMTransformation* trans = [ init];
temp = ;
</code></pre>
<p>同样，如果我尝试访问底层变量:</p>
<pre><code>CMTransformation* trans = [ init];
temp = ;
</code></pre>
<p>这两个都抛出异常，因为找不到 key 。我在这里错过了什么？</p>
<p><strong>上一个问题</strong></p>
<p>我编写了一些代码，允许我使用诸如“transformation.position”之类的字符串访问(有点)任意结构</p>
<p>由于某种原因，当我尝试从 NSObject 读取属性时，代码在第二次跳转时停止工作。这里是</p>
<pre><code>NSString* property = actionDetails[@"Property"];
PropertyParts = [ mutableCopy];
int count = ;
id current_object = initial_object;
for(int i = 0; i < count; i++)
{
NSString* current_part = PropertyParts;
current_object = ;
}
</code></pre>
<p>我已经尝试了所有可能的属性访问语法，包括 Property、property 和 _property。</p>
<p>这是自定义的 NSObject 声明</p>
<pre><code>#import <Foundation/Foundation.h>
#import <GLKit/GLKit.h>
@interface CMTransformation : NSObject
@property(nonatomic) GLKVector3 position;
@property(nonatomic) GLKVector3 scale;
@property(nonatomic) GLKVector3 rotation;
@property(nonatomic) GLKVector3 anchor;
@property(nonatomic) GLKMatrix4 matrix;
- (GLKMatrix4)calculateMatrixWithParentTransformation:(CMTransformation *)parentTransformation;
@end
</code></pre>
<p>另外，在第一个循环之后，我可以看到调试器说 CMTransformation* 正在填充 currrent_object，所以我不知道为什么我不能访问它的属性？</p></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><p>您对实现 <em>valueForUndefinedKey:</em> 和 <em>setValue:forUndefinedKey:</em> 满意吗？</p>
<p>如果是这样，这可行:</p>
<pre><code>union Test
{
CGFloat f ;
NSInteger i ;
};
@interface TestClass : NSObject
@property ( nonatomic ) union Test t ;
@end
@implementation TestClass
-(void)setValue:(nullable id)value forUndefinedKey:(nonnull NSString *)key
{
Ivar v = class_getInstanceVariable( [ self class ], [ [ NSString stringWithFormat:@"_%@", key ] UTF8String ] ) ;
if ( v )
{
char const * const encoding = ivar_getTypeEncoding( v ) ;
if ( encoding == '(' ) // unions only
{
size_t size = 0 ;
NSGetSizeAndAlignment( encoding, &size, NULL ) ;
uintptr_t ptr = (uintptr_t)self + ivar_getOffset( v ) ;
[ (NSValue*)value getValue:(void*)ptr ] ;
return ;
}
}
objc_property_t prop = class_getProperty( [ self class ], [ key UTF8String ] ) ;
if ( prop )
{
char const * const encoding = property_copyAttributeValue( prop, "T" ) ;
if ( encoding == '(' ) // unions only
{
objc_setAssociatedObject( self, NSSelectorFromString( key ), value, OBJC_ASSOCIATION_COPY ) ;
return ;
}
}
[ super setValue:value forUndefinedKey:key ] ;
}
-(nullable id)valueForUndefinedKey:(nonnull NSString *)key
{
Ivar v = class_getInstanceVariable( [ self class ], [ [ NSString stringWithFormat:@"_%@", key ] UTF8String ] ) ;
if ( v )
{
char const * const encoding = ivar_getTypeEncoding( v ) ;
if ( encoding == '(' )
{
size_t size = 0 ;
NSGetSizeAndAlignment( encoding, &size, NULL ) ;
uintptr_t ptr = (uintptr_t)self + ivar_getOffset( v ) ;
NSValue * result = [ NSValue valueWithBytes:(void*)ptr objCType:encoding ] ;
return result ;
}
}
objc_property_t prop = class_getProperty( [ self class ], [ key UTF8String ] ) ;
if ( prop )
{
return objc_getAssociatedObject( self, NSSelectorFromString( key ) ) ;
}
return [ super valueForUndefinedKey:key ] ;
}
@end
int main(int argc, const char * argv[])
{
@autoreleasepool
{
union Test u0 = { .i = 1234 } ;
TestClass * const testClass = [ TestClass new ] ;
[ testClass setValue:[ NSValue valueWithBytes:&u0 objCType:@encode( typeof( u0 ) ) ] forKey:@"t" ] ;
assert( testClass.t.i == 1234 ) ;
NSValue * const result = [ testClass valueForKey:@"t" ] ;
union Test u1 ;
[ result getValue:&u1 ] ;
assert( u1.i == 1234 ) ;
}
return 0;
}
</code></pre>
<p>(粘贴到你的main.m文件中试试)</p></p>
<p style="font-size: 20px;">关于ios - 在 Objective-C 中使用 KVC 读取联合属性，我们在Stack Overflow上找到一个类似的问题：
<a href="https://stackoverflow.com/questions/31006982/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/31006982/
</a>
</p>
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