CODEWITHSUNDEEP
swift3core-bluetooth
Chris
Chris

Reputation: 495

Get "value" from characteristic

The following...

    func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic, error: Error?) {
        print(characteristic)
    }

..outputs...

<CBCharacteristic: 0x1700b8180, UUID = FFE1, properties = 0x10, value = <01>, notifying = YES>

I want the "value" part "01".

Upvotes: 0

Views: 5580

Answers (4)

Hiral Jotaniya
Hiral Jotaniya

Reputation: 63

If you are asking to parse the data when Peripheral communicates.

func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor   characteristic: CBCharacteristic, error: Error?) {
    if let error = error {
        print("ERROR didUpdateValue \(error)")            
        return
    }
 //BLE_Characteristic_uuid > Your BLE Char UUID
    if characteristic.uuid == CBUUID(string: BLE_Characteristic_uuid) {
        guard let value = characteristic.value else { return }
        
        let content = String(data: value, encoding:.utf8)?.trimmingCharacters(in: .whitespacesAndNewlines) ?? ""//.filter { !" \n\t\r".contains($0) } ?? ""
        print("Value Received:-->",content )
        if let i = content.utf8.firstIndex(where: { $0 >= 32 })     {
           if let asciiPrefix = String(content.utf8[..<i]) {
             print(asciiPrefix)
            }
        }else{
            return
        }
    }
}

The ASCII value of 32 corresponds to the space character (' '). Therefore, the expression content.utf8.firstIndex(where: { $0 >= 32 }) returns the index of the first non-control character in the UTF-8 representation of the content String. However you can control it as per your requirements.

32 (in ASCII, these are printable characters like letters, digits, punctuation, etc.).

String(content.utf8[..<i]): This creates a new String using a substring of the content string from its start (0) up to the index i (excluding i). In other words, it extracts the portion of the string up to the first non-control ASCII character (whose ASCII value is greater than or equal to 32) and assigns it to asciiPrefix.

It will also neglect \u{01}

Upvotes: 0

Deepak Tagadiya
Deepak Tagadiya

Reputation: 2237

swift: Get value from characteristic while update value.

func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic, error: Error?) {

        let value = characteristic.value

        print(value)
}

Upvotes: -1

Chris
Chris

Reputation: 495

I want to thank OOPer on the Apple Developer Forums for this answer.

func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic, error: Error?) {  
    guard let data = characteristic.value else {  
        return  
    }  
    if data.elementsEqual([0x01]) { //<- You can directly compare a Data to an Array of bytes.  
        //do something  
    }
}

Upvotes: 0

ACBM
ACBM

Reputation: 667

According to the documentation you can access it by calling: characteristic.value, this will be an object of type Data. Then you can transform this object to string. Like this:

let data = characteristic.value
var dataString = String(data: data, encoding: String.Encoding.utf8)

Upvotes: 2

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