从objective-c中的主线程返回值

Question

我正在开发一个应用程序,我需要在后台线程中构建一些图像.在这个过程中的某个时刻,我需要从UITextView获取文本.如果我调用UITextview.text,我会收到警告,我的辅助线程不应该纠缠UIKit

这一切都很好,但我需要文本,我无法找出从主线程获得所述文本的合理方法.

我的问题是:有没有人想出一个很好的方法来从后台线程获取UI元素的属性,或者,首先避免这样做的好方法？

我把这个东西放在一起就可以了,但是感觉不对:

@interface SelectorMap : NSObject

@property (nonatomic, strong) NSArray *selectors;
@property (nonatomic, strong) NSArray *results;

@end


@interface NSObject (Extensions)
- (NSArray *)getValuesFromMainThreadWithSelectors:(SEL)selector, ...;
- (void)performSelectorMap:(SelectorMap *)map;
@end

并实施:

#import "NSObject+Extensions.h"

@implementation SelectorMap
@synthesize selectors;
@synthesize results;
@end

@implementation NSObject (Extensions)

- (void)performSelectorMap:(SelectorMap *)map
{
    NSMutableArray *results = [NSMutableArray arrayWithCapacity:map.selectors.count];

    for (NSString *selectorName in map.selectors)
    {
        SEL selector = NSSelectorFromString(selectorName);
        id result = [self performSelector:selector withObject:nil];
        [results addObject:result];
    }

    map.results = results.copy;
}

- (NSArray *)getValuesFromMainThreadWithSelectors:(SEL)selector, ...
{
    NSMutableArray *selectorParms = [NSMutableArray new];

    va_list selectors;
    va_start(selectors, selector);

    for (SEL selectorName = selector; selectorName; selectorName = va_arg(selectors, SEL))
        [selectorParms addObject:NSStringFromSelector(selectorName)];

    va_end(selectors);

    SelectorMap *map = [SelectorMap new];
    map.selectors = selectorParms.copy;

    [self performSelectorOnMainThread:@selector(performSelectorMap:) withObject:map waitUntilDone:YES];

    return map.results;
}

@end

我称之为:

NSArray *textViewProperties = [textView getValuesFromMainThreadWithSelectors:@selector(text), @selector(font), nil];

获取字体并没有给出获取文本的相同警告,但我认为最好保持一致.

Answer 1

我尽可能避免使用任何类型的元编程.它完全破坏了编译器重复检查代码的能力,对于启动,它往往是不可读的.

 __block NSString* foo;
 dispatch_sync(dispatch_get_main_queue(), ^{
      foo = [textField ...];
  });

请注意,如果不使用ARC,您可能想要copy或者retain在块中然后release或autorelease在本地线程中使用字符串.