特別注意：定義的command中的封裝信號一定要sendCompleted；否則在生命周期內(nèi)無法被重新激活；

1. 普通的command

普通的RACCommand的使用很簡單了，只需要在封裝的信號中sendCompleted、sendError就可以。例如：

- (RACCommand *)commandForDataSelecting {
  if (!_commandForDataSelecting) {
    @weakify(self);
    _commandForDataSelecting = [[RACCommand alloc] initWithSignalBlock:^RACSignal *(id input) {
        return [[RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
            @strongify(self);
            [[DBManager sharedDB] selectDataFromTabel:kCardInfoTableName forConditions:nil sucBlock:^(NSArray *datasSelected) {
                [subscriber sendCompleted];
            } errBlock:^(NSError *error) {
                [subscriber sendError:error];
            }];
            return nil;
        }] replayLast];
    }];
  }
  return _commandForDataSelecting;
}

2. 獲取響應(yīng)狀態(tài)

要處理的狀態(tài)有3種：開始,完成,失敗

• 開始

  [[command executing] subscribeNext:^id(id x) {
      NSLog(@"數(shù)據(jù)加載中...");
  } // 或者在 'subscribeNext' 前面加上 'deliverOn:' 在主線程中處理;
  

• 完成

  [[[command executionSignals] flattenMap:^ RACStream(RACSignal* innerSignal) {
      return [innerSignal materialize];
  }] subscribeNext:^(RACEvent* event) {
      if (event.eventType == RACEventTypeCompleted) {
          NSLog(@"數(shù)據(jù)加載完畢!"); // 1
      }
      else if (event.eventType == RACEventTypeError) {
          NSLog(@"數(shù)據(jù)加載失敗!"); //2
      }
      else if (event.eventType == RACEventTypeNext) {
          NSLog(@"數(shù)據(jù)加載中..."); //3
      }
  }];
  

實際測試發(fā)現(xiàn)，subscribeNext只能獲取到 completed的狀態(tài)，所以可以在 subscribeNext 前對結(jié)果進行過濾:filter:,過濾出completed的狀態(tài)。

• 失敗

  [[command errors] subscribeNext:^(NSError* error) {
      NSLog(@"%@",[error localizedDescription]); //4
  }
  

3. 疑惑和解惑

• 當(dāng)command能正常結(jié)束時，一切都沒問題?？墒钱?dāng)command執(zhí)行異常時，不僅異常errors被拋出://4，completed也被拋出了//1。
• 如果上面 // 1-4 都用蒙版 MBProgressHUD 顯示的話，線程調(diào)度會有問題，蒙版顯示會一閃而過；

所以，我們要解決的目標(biāo)：當(dāng) command 拋出 error 時，不要同時拋出 completed .

• 解決方法
  在command的定義中，將返回的RACSignal再次封裝materialize，封裝后產(chǎn)生的信號的值是RACEvent類型；
  然后executionSignals通過解封裝dematerialize出一個新的信號,對它進行'異常'、'完成'捕獲:subscribeError: completed:分別處理異常和完成狀態(tài).

新的command定義和executionSignals處理如下:

// command定義
- (RACCommand *)commandForDataSelecting {
  if (!_commandForDataSelecting) {
    @weakify(self);
    _commandForDataSelecting = [[RACCommand alloc] initWithSignalBlock:^RACSignal *(id input) {
        return [[[[RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
            @strongify(self);
            [[DBManager sharedDB] selectDataFromTabel:kCardInfoTableName forConditions:nil sucBlock:^(NSArray *datasSelected) {
                self.cardInfosSelected = [datasSelected copy];
                [subscriber sendCompleted];
            } errBlock:^(NSError *error) {
                [subscriber sendError:error];
            }];
            return nil;
        }] replayLast] materialize] delay:1];
    }];
  }
  return _commandForDataSelecting;
}

 // 結(jié)果處理
 [command.executionSignals subscribeNext:^(RACSignal* signal) {
    @strongify(self);
    [[[signal dematerialize] deliverOn:[RACScheduler mainThreadScheduler]] subscribeError:^(NSError *error) {
        [self.progressHUD showFailWithText:[error localizedDescription] andDetailText:nil onCompletion:nil];
    } completed:^{
        [self.progressHUD showSuccessWithText:@"加載成功" andDetailText:nil onCompletion:^{}];
    }];
}];