If you're developing a mobile application using Apache Cordova and you're facing issues with Bluetooth Low Energy (BLE) printing via the cordova-plugin-ble-central, you're not alone. Many developers have encountered the frustrating situation where the ble.write method does not return any error, yet the expected print job does not occur.
Understanding the Problem
In this article, we will address the specific issue: "Can't get print via cordova-plugin-ble-central ble.write, while it doesn't return any error (Android)." The original code snippet that might resemble the issue is as follows:
// Example code that attempts to write data to a BLE device
ble.write(deviceId, serviceUUID, characteristicUUID, data,
function() {
console.log('Write successful');
},
function(error) {
console.error('Write failed: ' + error);
}
);
While the above code seems correct, you may find that the console logs 'Write successful,' yet nothing gets printed. Let's delve deeper into understanding and resolving this issue.
Analyzing the Issue
1. Ensure Correct UUIDs
The first thing to check is whether you are using the correct serviceUUID and characteristicUUID. These UUIDs are vital because they tell the device which service and characteristic to communicate with. If they're incorrect, the device may not respond even though there's no error.
2. Data Format
The format of the data you're trying to write also plays a crucial role. Ensure that the data you're sending to the printer is in the correct byte format. BLE devices often expect data in specific structures. If you’re sending strings, make sure to convert them to a byte array or to the required format that the printer can interpret.
3. BLE Connection Status
Sometimes, the connection to the BLE device might be unstable. Double-check that the device is connected before sending any write commands. You can implement a connection check by listening for the state changes in the BLE connection.
4. Firmware and Compatibility
Occasionally, the issue may lie with the firmware of the BLE printer. Ensure that your printer supports the command you are trying to send. Refer to the printer’s technical documentation to validate compatibility with the BLE commands.
5. Permissions and Background Restrictions
For Android applications, ensure that you have all necessary permissions set correctly in your Android manifest. Additionally, check the background execution settings, as Android may restrict background operations depending on the device’s settings.
Practical Example
To illustrate these points, consider the following example:
var deviceId = 'YOUR_DEVICE_ID';
var serviceUUID = 'YOUR_SERVICE_UUID';
var characteristicUUID = 'YOUR_CHARACTERISTIC_UUID';
var data = new Uint8Array([0x1B, 0x40, 0x01, 0x02, 0x03]); // Sample data format
ble.write(deviceId, serviceUUID, characteristicUUID, data.buffer,
function() {
console.log('Write successful');
},
function(error) {
console.error('Write failed: ' + error);
}
);
In this example, we utilize a Uint8Array to format the data being sent. Always consult your printer’s documentation to match the expected data structure.
Conclusion
In summary, when dealing with BLE printing issues in Apache Cordova applications using cordova-plugin-ble-central, it’s crucial to check your UUIDs, format your data correctly, ensure stable connectivity, verify compatibility with the printer, and handle permissions properly. By following these steps, you can troubleshoot and resolve many common issues that arise in this context.
Useful Resources
By optimizing your troubleshooting strategies, you can enhance your application's performance and ensure a smoother user experience with BLE printing.
