performSelector方法
- performSelector在运行时，调用方去找目标方法selector，在编译时不做校验；
延迟执行 -- 与RunLoop有关
- 调用performSelector:withObject:afterDelay方法实现延迟执行，底层的本质是会创建NSTimer定时器去执行目标方法selector；
- (void)viewDidLoad {
[super viewDidLoad];
[self performSelector:@selector(test) withObject:nil afterDelay:3];
}
- (void)test {
NSLog(@"%s",__func__);
NSLog(@"%@",[NSThread currentThread]);
}
@end
- 在主线程中，延迟3秒后执行test方法，可以执行成功；
- 若将performSelector:withObject:afterDelay方法 放在子线程中调用，如下：
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
dispatch_async(dispatch_get_global_queue(0, 0), ^{
[self performSelector:@selector(test) withObject:nil afterDelay:3];
});
}
- (void)test {
NSLog(@"%s",__func__);
NSLog(@"%@",[NSThread currentThread]);
}
@end
- 在子线程中调用performSelector:withObject:afterDelay方法 是不会执行test方法的，因为NSTimer定时器依赖于RunLoop才能执行，必须开启子线程的RunLoop，做如下修改：
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
dispatch_async(dispatch_get_global_queue(0, 0), ^{
[self performSelector:@selector(test) withObject:nil afterDelay:3];
[[NSRunLoop currentRunLoop] run];
});
}
- (void)test {
NSLog(@"%s",__func__);
NSLog(@"%@",[NSThread currentThread]);
}
@end
开启子线程执行任务 -- 与多线程有关
- performSelector: onThread:withObject: waitUntilDone: 可指定线程执行目标方法任务；
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
dispatch_async(dispatch_get_global_queue(0, 0), ^{
NSLog(@"%@",[NSThread currentThread]);
NSLog(@"11111");
[self performSelector:@selector(test) onThread:[NSThread currentThread] withObject:nil waitUntilDone:YES];
NSLog(@"22222");
});
}
- (void)test {
NSLog(@"%s",__func__);
NSLog(@"%@",[NSThread currentThread]);
}
@end
- 控制台的调试结果如下：
image.png
- performSelector发送消息与消息的执行是处于
同一个线程的； - waitUntilDone参数为Yes，表示test方法必须执行完成，才会执行之后的打印2222，即会阻塞当前线程的继续执行；
performSelector:方法传递多参数的实现方案
- 第一种方案：将所有参数放到字典或者数组中，再传递集合即可；
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
NSDictionary *params = @{
@"name":@"yanzi",
@"age":@"30"
};
[self performSelector:@selector(test:) withObject:params];
}
- (void)test:(NSDictionary *)params {
NSLog(@"%@--%@",params[@"name"],params[@"age"]);
}
@end
- 第二种方案：利用objc_msgSend()进行传递，其可以传递多个参数；
#import "ViewController.h"
#import <objc/message.h>
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
((void (*)(id,SEL,NSString *, NSString *, NSString *))objc_msgSend)(self, @selector(testWithParam:param2:param3:),@"111",@"222",@"333");
}
//有三个参数的方法
- (void)testWithParam:(NSString *)param1 param2:(NSString *)param2 param3:(NSString *)param3 {
NSLog(@"param1:%@, param2:%@, param3:%@",param1, param2, param3);
}
@end
- 第三种方案：利用NSInvocation进行传递
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
//调用方法
NSArray *paramArray = @[@"112",@[@2,@13],@12];
[self performSelector:@selector(testFunctionWithParam:param2:param3:) withObjects:paramArray];
}
//可以传多个参数的方法
- (id)performSelector:(SEL)selector withObjects:(NSArray *)objects{
// 方法签名(方法的描述)
NSMethodSignature *signature = [[self class] instanceMethodSignatureForSelector:selector];
if (signature == nil) {
//可以抛出异常也可以不操作。
}
//NSInvocation: 利用一个NSInvocation对象包装一次方法调用（方法调用者、方法名、方法参数、方法返回值）
NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];
invocation.target = self;
invocation.selector = selector;
//设置参数
NSInteger paramsCount = signature.numberOfArguments - 2; // 除self、_cmd以外的参数个数
paramsCount = MIN(paramsCount, objects.count);
for (NSInteger i = 0; i < paramsCount; i++) {
id object = objects[i];
if ([object isKindOfClass:[NSNull class]]) continue;
[invocation setArgument:&object atIndex:i + 2];
}
//调用方法
[invocation invoke];
//获取返回值
id returnValue = nil;
if (signature.methodReturnLength) { // 有返回值类型，才去获得返回值
[invocation getReturnValue:&returnValue];
}
return returnValue;
}
//要调用的方法
- (void)testFunctionWithParam:(NSString *)param1 param2:(NSArray *)param2 param3:(NSInteger)param3 {
NSLog(@"param1:%@, param2:%@, param3:%ld",param1, param2, param3);
}
@end
