帶多個參數的performSelectorInBackground

Question

如何使用performSelectorInBackground調用多個參數，如下所示：

樣品方法：

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

Answer 1

的問題是，performSelectorInBackground:withObject:只需要一個對象參數。要繞過這個限制的一種方式是通過的參數的字典（或陣列）到解構參數和調用您的實際方法的「包裝」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... 
}

這樣，你只傳遞一個「單一「的背景調用的參數，但該方法可以構建真正調用所需的多個參數（這將發生在同一個背景線上）。

Answer 2

好了，我已經使用這個：

[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

我只是發現了這個問題，並沒有高興與任何答案。在我看來，既沒有充分利用現有的工具，也沒有在數組和字典中傳遞任意信息，這通常令我感到擔憂。

於是，我又寫了一個小NSObject的類別，將與參數個數可變調用任意選擇：

Category接頭

@interface NSObject (NxAdditions) 

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

@end 

分類實施

@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

與performSelectorInBackground你只能傳遞一個參數，所以使自定義對象的這個方法來保存數據，ITLL比曖昧字典或數組更加簡潔。這樣做的好處是，當包含多個返回屬性時，您可以傳遞相同的對象。

#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 

和對象傳遞給你的方法：

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; 
} 

確保清理對象做是爲了防止內存泄漏