Question

如何使用performSelectorInBackground调用带有多个params的方法？

示例方法：

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

Answer 1

问题是performSelectorInBackground:withObject:只接受一个对象参数。解决此限制的一种方法是将参数的字典（或数组）传递给“包装器”方法，该方法解构参数并调用实际方法：

- (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...
}

这样你只是将“单个”参数传递给后台调用，但是该方法可以构造真实调用所需的多个参数（这将在同一个后台运行的线程上进行）。

Answer 2

我刚刚发现了这个问题，对任何答案都不满意。在我看来，两者都没有充分利用可用的工具，并且在数组和字典中传递任意信息一般都让我担心。

所以，我去写了一个小NSObject类，它将调用一个带有可变数量参数的任意选择器：

类别标题

@interface NSObject (NxAdditions)

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

@end

类别实施

@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

<强>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 3

好吧，我用过这个：

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

为此：

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

Answer 4

使用performSelectorInBackground

你只能传递一个参数，所以为这个方法创建一个自定义对象来保存你的数据，它比一个模糊的字典或数组更简洁。这样做的好处是，当完成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

并将该对象传递给您的方法：

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;
}

确保在完成后清理对象以防止内存泄漏

performSelectorInBackground有多个参数

4 个答案: