CODEWITHSUNDEEP
iosobjective-ccore-bluetooth
iosdeveloper
iosdeveloper

Reputation: 99

iOS CoreBluetooth:Sending data from central and getting response from peripheral

I am developing a Bluetooth app. I have connected to the bluetooth device and found the services and characteristics in it. I am facing problem in sending write request from central and receiving response from peripheral. I have written code as below to write data. How will I know that peripheral received that data? Can I show any alert in peripheral. And, in the same way, I want to receive the data from the peripheral so that the central should show an alert that it has got response from peripheral.

Here is the below code I have written 

  - (void)peripheral:(CBPeripheral *)peripheral didDiscoverCharacteristicsForService:  
  (CBService *)service error:(NSError *)error {
   if (!error) {
    printf("Characteristics of service with UUID : %s found\r\n",[self   
   CBUUIDToString:service.UUID]);
    for(int i=0; i < service.characteristics.count; i++) {
        CBCharacteristic *c = [service.characteristics objectAtIndex:i];
        printf("Found characteristic %s\r\n",[ self CBUUIDToString:c.UUID]);
        CBService *s = [peripheral.services objectAtIndex:(peripheral.services.count - 1)];
        if([self compareCBUUID:service.UUID UUID2:s.UUID])
        {
            printf("Finished discovering characteristics");

            break;
        }
     }

  }
   else {
    printf("Characteristic discorvery unsuccessfull !\r\n");
  }

  }

for writing the value 

- (void)peripheral:(CBPeripheral *)peripheral didUpdateValueForCharacteristic:  
   (CBCharacteristic *)characteristic error:(NSError *)error
  {
    NSString *payloadMessage = @"Hello";
    NSData *payload = [payloadMessage dataUsingEncoding:NSUTF8StringEncoding];
    [peripheral writeValue:payload forCharacteristic:characteristic    
   type:CBCharacteristicWriteWithResponse];

 }

and i need to get the version of the ble device i.e GET_VERSION = 0x4a; please help me regarding this or else provide any examples for writing and reading data from the both devices.Thanks in advance

Upvotes: 0

Views: 6272

Answers (1)

Paulw11
Paulw11

Reputation: 114846

There are two ways that a Bluetooth central can receive data from a peripheral -

  1. It can issue an explicit read request for a characteristic
  2. It can subscribe for notifications on a characteristic - in this case the peripheral will notify the central when the value changes or these is new data. This is more efficient as it avoids the central having to constantly poll the peripheral for data that may not have changed.

Regards of which method you use, the data will be delivered via a call to your didUpdateValueForCharacteristic: delegate method.

It seems you are a bit confused as to the purpose of this method as your code issues a write request there, which probably isn't what you want.

When it comes to writing data, you can write the data with or without a response. Your code specifies with response. In this case, when the peripheral acknowledges the write, your didWriteValueForCharacteristic delegate method is called - this is how you know that the data was received.

Some simple code to implement the behaviour you described in your question is:

 -(void)sendData:(NSData *)data {

      [self.connectedPeripheral writeValue:data forCharacteristic:self.someCharacteristic type:CBCharacteristicWriteWithResponse];

 }


- (void)peripheral:(CBPeripheral *)peripheral
didWriteValueForCharacteristic:(CBCharacteristic *)characteristic
             error:(NSError *)error {
         if (error == nil) {
            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Wrote characteristic" message:@"Successfully wrote characteristic" delegate:nil cancelButtonTitle:nil otherButtonTitles:@"ok"];
            [alert show];
         }
         else {
             NSLog(@"Error writing characteristic %@",error);
         }
     }

  -(void)readCharacteristic {
    [self.connectedPeripheral readCharacteristic:self.someOtherCharacteristic];
}




- (void)peripheral:(CBPeripheral *)peripheral didUpdateValueForCharacteristic:(CBCharacteristic *)characteristic error:(NSError *)error
    {
     if (error == nil) {
            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Read characteristic" message:[NSString stringWithFormat:@"Successfully read characteristic %@",characteristic.value] delegate:nil cancelButtonTitle:nil otherButtonTitles:@"ok"];
            [alert show];
         }
         else {
             NSLog(@"Error reading characteristic %@",error);
         }

     }

Upvotes: 3

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