带多个参数的performSelectorInBackground

Question

如何使用performSelectorInBackground调用多个参数，如下所示：

样品方法：

-(void) reloadPage:(NSInteger)pageIndex firstCase:(BOOL)firstCase; 

Answer 1

的问题是，performSelectorInBackground:withObject:只需要一个对象参数。要绕过这个限制的一种方式是通过的参数的字典（或阵列）到解构参数和调用您的实际方法的“包装”方法：

- (void)callingMethod { 
    NSDictionary * args = [NSDictionary dictionaryWithObjectsAndKeys: 
          [NSNumber numberWithInteger:pageIndex], @"pageIndex", 
          [NSNumber numberWithBool:firstCase], @"firstCase", 
          nil]; 
    [self performSelectorInBackground:@selector(reloadPageWrapper:) 
          withObject:args]; 
} 

- (void)reloadPageWrapper:(NSDictionary *)args { 
    [self reloadPage:[[args objectForKey:@"pageIndex"] integerValue] 
      firstCase:[[args objectForKey:@"firstCase"] boolValue]]; 
} 

- (void)reloadPage:(NSInteger)pageIndex firstCase:(BOOL)firstCase { 
    // Your code here... 
}

这样，你只传递一个“单一“的背景调用的参数，但该方法可以构建真正调用所需的多个参数（这将发生在同一个背景线上）。

Answer 2

好了，我已经使用这个：

[self performSelectorInBackground:@selector(reloadPage:) 
         withObject:[NSArray arrayWithObjects:pageIndex,firstCase,nil] ]; 

此：

- (void) reloadPage: (NSArray *) args { 
    NSString *pageIndex = [args objectAtIndex:0];  
    NSString *firstCase = [args objectAtIndex:1];  
} 

Answer 3

我只是发现了这个问题，并没有高兴与任何答案。在我看来，既没有充分利用现有的工具，也没有在数组和字典中传递任意信息，这通常令我感到担忧。

于是，我又写了一个小NSObject的类别，将与参数个数可变调用任意选择：

Category接头

@interface NSObject (NxAdditions) 

-(void)performSelectorInBackground:(SEL)selector withObjects:(id)object, ... NS_REQUIRES_NIL_TERMINATION; 

@end 

分类实施

@implementation NSObject (NxAdditions) 

-(void)performSelectorInBackground:(SEL)selector withObjects:(id)object, ... 
{ 
    NSMethodSignature *signature = [self methodSignatureForSelector:selector]; 

    // Setup the invocation 
    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature]; 
    invocation.target = self; 
    invocation.selector = selector; 

    // Associate the arguments 
    va_list objects; 
    va_start(objects, object); 
    unsigned int objectCounter = 2; 
    for (id obj = object; obj != nil; obj = va_arg(objects, id)) 
    { 
     [invocation setArgument:&obj atIndex:objectCounter++]; 
    } 
    va_end(objects); 

    // Make sure to invoke on a background queue 
    NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithInvocation:invocation]; 
    NSOperationQueue *backgroundQueue = [[NSOperationQueue alloc] init]; 
    [backgroundQueue addOperation:operation]; 
} 

@end 

用法

-(void)backgroundMethodWithAString:(NSString *)someString array:(NSArray *)array andDictionary:(NSDictionary *)dict 
{ 
    NSLog(@"String: %@", someString); 
    NSLog(@"Array: %@", array); 
    NSLog(@"Dict: %@", dict); 
} 

-(void)someOtherMethod 
{ 
    NSString *str = @"Hello world"; 
    NSArray *arr = @[@(1337), @(42)]; 
    NSDictionary *dict = @{@"site" : @"Stack Overflow", 
          @"url" : [NSURL URLWithString:@"http://stackoverflow.com"]}; 

    [self performSelectorInBackground:@selector(backgroundMethodWithAString:array:andDictionary:) 
          withObjects:str, arr, dict, nil]; 
} 

Answer 4

与performSelectorInBackground你只能传递一个参数，所以使自定义对象的这个方法来保存数据，ITLL比暧昧字典或数组更加简洁。这样做的好处是，当包含多个返回属性时，您可以传递相同的对象。

#import <Foundation/Foundation.h> 

@interface ObjectToPassToMethod : NSObject 

@property (nonatomic, strong) NSString *inputValue1; 
@property (nonatomic, strong) NSArray *inputArray; 
@property (nonatomic) NSInteger returnValue1; 
@property (nonatomic) NSInteger returnValue2; 

@end 

和对象传递给你的方法：

ObjectToPassToMethod *obj = [[ObjectToPassToMethod alloc] init]; 
obj.inputArray = @[]; 
obj.inputValue1 = @"value"; 
[self performSelectorInBackground:@selector(backgroundMethod:) withObject:obj]; 


-(void)backgroundMethod:(ObjectToPassToMethod*)obj 
{ 
    obj.returnValue1 = 3; 
    obj.returnValue2 = 90; 
} 

确保清理对象做是为了防止内存泄漏