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Android BLE GATT Operations — Complete Guide

DodaTech Updated 2026-06-24 2 min read

In this tutorial, you'll learn about Android BLE GATT Operations. We cover key concepts, practical examples, and best practices to help you understand and apply this topic effectively.

The Problem

Your BLE read returns GATT_INVALID_ATTRIBUTE_LENGTH, or you never receive notifications after enabling them.

Wrong Approach ❌

// Reading characteristic without checking properties
gatt.readCharacteristic(characteristic) // May not be readable!

// Enabling notifications without descriptor
gatt.setCharacteristicNotification(characteristic, true)
// Forgot to write CCCD descriptor!

Output: Read fails with GATT_READ_NOT_PERMITTED. Notifications never arrive.

Right Approach ✅

class GattOperationManager(private val gatt: BluetoothGatt) {

    // Safe characteristic read
    fun readCharacteristic(char: BluetoothGattCharacteristic) {
        if (!containsProperty(char, BluetoothGattCharacteristic.PROPERTY_READ)) {
            Log.e("GattOp", "Characteristic not readable")
            return
        }
        gatt.readCharacteristic(char)
    }

    // Write with response
    fun writeCharacteristic(char: BluetoothGattCharacteristic, data: ByteArray) {
        if (!containsProperty(char, BluetoothGattCharacteristic.PROPERTY_WRITE)) {
            Log.e("GattOp", "Characteristic not writable")
            return
        }
        char.value = data
        char.writeType = BluetoothGattCharacteristic.WRITE_TYPE_DEFAULT
        gatt.writeCharacteristic(char)
    }

    // Write without response (faster, no ACK)
    fun writeCharacteristicWithoutResponse(char: BluetoothGattCharacteristic, data: ByteArray) {
        if (!containsProperty(char, BluetoothGattCharacteristic.PROPERTY_WRITE_NO_RESPONSE)) {
            Log.e("GattOp", "Characteristic not writable without response")
            return
        }
        char.value = data
        char.writeType = BluetoothGattCharacteristic.WRITE_TYPE_NO_RESPONSE
        gatt.writeCharacteristic(char)
    }

    // Enable notifications
    fun enableNotifications(char: BluetoothGattCharacteristic) {
        if (!containsProperty(char, BluetoothGattCharacteristic.PROPERTY_NOTIFY)) {
            Log.e("GattOp", "Characteristic does not support notifications")
            return
        }

        gatt.setCharacteristicNotification(char, true)

        // Write CCCD (Client Characteristic Configuration Descriptor)
        val cccd = char.getDescriptor(
            UUID.fromString("00002902-0000-1000-8000-00805f9b34fb")
        ) ?: run {
            Log.e("GattOp", "CCCD not found")
            return
        }

        cccd.value = BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE
        gatt.writeDescriptor(cccd)
    }

    // Enable indications
    fun enableIndications(char: BluetoothGattCharacteristic) {
        if (!containsProperty(char, BluetoothGattCharacteristic.PROPERTY_INDICATE)) {
            Log.e("GattOp", "Characteristic does not support indications")
            return
        }

        gatt.setCharacteristicNotification(char, true)
        val cccd = char.getDescriptor(CCCD_UUID)
        cccd?.let {
            it.value = BluetoothGattDescriptor.ENABLE_INDICATION_VALUE
            gatt.writeDescriptor(it)
        }
    }

    // Read descriptor
    fun readDescriptor(descriptor: BluetoothGattDescriptor) {
        gatt.readDescriptor(descriptor)
    }

    // Handle response in BluetoothGattCallback:
    // onCharacteristicRead, onCharacteristicWrite, onDescriptorWrite
    // onCharacteristicChanged (notification/indication)

    private fun containsProperty(char: BluetoothGattCharacteristic, property: Int): Boolean {
        return char.properties and property != 0
    }

    companion object {
        val CCCD_UUID = UUID.fromString("00002902-0000-1000-8000-00805f9b34fb")
    }
}

// Callback handlers
override fun onCharacteristicChanged(gatt: BluetoothGatt, characteristic: BluetoothGattCharacteristic) {
    val data = characteristic.value
    // Handle notification data
}

Output: Correct GATT operations with property checking.

Prevention

  • Always check characteristic properties before read/write.
  • Always write CCCD descriptor after setCharacteristicNotification.
  • Use WRITE_TYPE_NO_RESPONSE for high-throughput, lossy-tolerant data.
  • Queue operations — BLE is single-threaded per GATT connection.

Common Mistakes with bluetooth gatt

  1. Using return to exit a function early instead of wrapping a pure value in the monad
  2. Mixing let bindings with <- bindings in do notation, producing type errors
  3. Overlapping type class instances that cause GHC to reject the program with ambiguous dispatch errors

These mistakes appear frequently in real-world Android code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

FAQ

### Why do I need to write the CCCD descriptor?

The CCCD (0x2902) tells the peripheral to start sending notifications/indications. Without it, the peripheral won't send data even if you call setCharacteristicNotification.

### What is the difference between notification and indication?

Notifications have no acknowledgement (faster, may miss data). Indications have acknowledgement (guaranteed delivery, slower). Use indications for critical data.

### How do I handle long data (more than MTU)?

BLE has a maximum packet size of MTU. For larger data, either: (1) request larger MTU, (2) implement manual segmentation and reassembly, or (3) use L2CAP CoC.

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