I am new in flutter.
I am building an app to print on the ble label printer via Bluetooth.
I use flutter_blue library. I had successfully connected to the device and found the target characteristic. My problem is that when I call write() function of the characteristic printer show on display “waiting for data” and nothing is printed.
Could you please help me with the data format I need to put into the method?
I use utf8 encoded string as data.
Future<void> _print() async {
var serviceUuid = '0000ff00-0000-1000-8000-00805f9b34fb';
var characteristicsUuid = '0000ff02-0000-1000-8000-00805f9b34fb';
_services.forEach((service) {
if(service.uuid.toString().toLowerCase() == serviceUuid) {
printService = service;
for (var c in printService!.characteristics) {
if(c.uuid.toString().toLowerCase() == characteristicsUuid) {
var ZPL_TEST_LABEL = 'Hello WeChat!\r\n';
printCharacteristic = c;
writeData(printCharacteristic, ZPL_TEST_LABEL);
}
}
}});
}
Future<void> writeData(characteristic, data) async{
if (characteristic == null) return;
try {
var utf8Encoded = utf8.encode(data);
debugPrint(data.toString());
var result = await characteristic.write(utf8Encoded);
debugPrint(result.toString());
} catch (e) {
debugPrint(e.toString());
}
}
My first step is to print at least a string, could you pls help me?
Related
I am trying to create model and parse json data from api
for that i created the model class you can see below
class FeatureModel {
String? PlanFeatures;
bool? FeatureStatus;
FeatureModel({this.PlanFeatures, this.FeatureStatus});
FeatureModel.fromJson(parsonJson) {
PlanFeatures = parsonJson['PlanFeatures'];
FeatureStatus = parsonJson['FeatureStatus'];
}
}
now i am trying to parse json with the help of loop
let me show you my method
List<FeatureModel> featureModel = [];
Uri featureAPI = Uri.parse(
planFeatureApi);
apiCall() async {
try {
http.Response response = await http.get(featureAPI);
// print(response.statusCode);
if (response.statusCode == 200) {
var decode = json.decode(response.body);
print(decode);
for (var i = 0; i < decode.length; i++) {
print(i);
featureModel.add(
FeatureModel.fromJson(decode[i]),
);
}
}
} catch (e) {}
}
I am calling it here
onPressed: () async{
await apiCall();
}
but the problem is here
loop is not working while parsing data
in that particular code i remains on 0 only
when i removes featureModel.add( FeatureModel.fromJson(decode[i]), ); i started increaing till 10
please let me know if i am making any mistake or what
thanks in advance
Here is the sample of api respone
[{"PlanFeatures":"Video Link Sharing","FeatureStatus":"true"},{"PlanFeatures":"Email \u0026amp; Telephonic Support","FeatureStatus":"true"},{"PlanFeatures":"Remove Pixeshare Branding","FeatureStatus":"false"},{"PlanFeatures":"Add Custom logo on uploaded photos","FeatureStatus":"false"},{"PlanFeatures":"Get Visitor Info","FeatureStatus":"false"},{"PlanFeatures":"Mobile Apps","FeatureStatus":"false"},{"PlanFeatures":"Send Questionnaries","FeatureStatus":"false"},{"PlanFeatures":"Create \u0026amp; Send Quotation","FeatureStatus":"false"},{"PlanFeatures":"Online Digital Album Sharing","FeatureStatus":"false"},{"PlanFeatures":"Analytics","FeatureStatus":"false"}]
thanks
I found many errors, first, the fromJson is not a factory constructor and doesn't return a class instance from the JSON.
the second one is that the bool values from the sample you added are String not a bool so we need to check over it.
try changing your model class to this:
class FeatureModel {
String? PlanFeatures;
bool? FeatureStatus;
FeatureModel({this.PlanFeatures, this.FeatureStatus});
factory FeatureModel.fromJson(parsonJson) {
return FeatureModel(
PlanFeatures: parsonJson['PlanFeatures'],
FeatureStatus: parsonJson['FeatureStatus'] == "false" ? false : true,
);
}
}
In my app, a user can send a file to others in a group chat. First, the user records some audio using their mic. The file is then touched up using FFMPEG. Then, the file is uploaded to Firebase Cloud Storage and if this is successful, a record is written in Firebase Realtime Database.
I'm getting the error below when the user records a long audio file and then presses submit. It almost seems as though FFMPEG hasn't finished processing the file...but I thought I used my async/await correctly to make sure that this processing is finished before moving on?
##MyAppFile## saveMyAppFileToCloudStorage Error: 'package:firebase_storage/src/reference.dart': Failed assertion: line 127 pos 12: 'file.absolute.existsSync()': is not true.
Psuedo-code:
User records audio
Audio file is processed using FFMPEG and the new processed file is created on the user's phone
User hits submit, uploading the file to Cloud Storage and, if successful, writing a record to Realtime Database
Order of Functions After User Hits Submit:
msgInput.dart -> sendMyAppFile()
msgInput.dart -> prepareMyAppFileForSending()
msgInput.dart -> runFFMPEGHighLow()
message_dao.dart -> sendMyAppFile()
message_dao.dart -> saveMyAppFileToCloudStorage() //ERROR COMES FROM THIS FUNCTION
The Code:
//msgInput.dart
Future<void> sendMyAppFile() async {
if (sendableMyAppFileExists == 1) {
final MyAppFileReadyToBeSent = await prepareMyAppFileForSending();
if (MyAppFileReadyToBeSent == '1') {
messageDao.sendMyAppFile(MyAppFile, filepath, filename);
} else {
}
}
setState(() {
sendableMyAppFileExists = 0;
});
}
Future<String> prepareMyAppFileForSending() async {
if (sendableMyAppFileExists == 1) {
if (recordedMyAppFileFilterID == '1') {
await runFFMPEGHighLow('1');
return '1';
}
if (recordedMyAppFileFilterID == '2') {
await runFFMPEGHighLow('2');
return '1';
}
}
return '0';
}
Future<void> runFFMPEGHighLow(String filterID) async {
if (filterID != '1' && filterID != '2') {
return;
}
if (sendableMyAppFileExists == 1) {
if (filterID == '1') {
await FFmpegKit.executeAsync(/*...parms...*/);
setState(() {
currentMyAppFileFilename = currentMyAppFileFilename + '1.mp3';
});
}
if (filterID == '2') {
await FFmpegKit.executeAsync(/*...parms...*/);
setState(() {
currentMyAppFileFilename = currentMyAppFileFilename + '2.mp3';
});
}
}
}
//message_dao.dart
void sendMyAppFile(ChatData MyAppFile, String filepath, String filename) {
saveMyAppFileToCloudStorage(filepath, filename).then((value) {
if (value == true) {
saveMyAppFileToRTDB(MyAppFile);
}
});
}
Future<bool> saveMyAppFileToCloudStorage(String filepath, String filename) async {
//filepath: /data/user/0/com.example.MyApp/app_flutter/MyApp/MyAppAudioFiles/MyAppFiles/2d7af6ae-6361-4be5-8209-8498dd17d77d1.mp3
//filename: 2d7af6ae-6361-4be5-8209-8498dd17d77d1.mp3
_firebaseStoragePath = MyAppFileStorageDir + filename;
File file = File(filepath);
try {
await _firebaseStorage
.ref(_firebaseStoragePath)
.putFile(file);
return true;
} catch (e) {
print('##MyAppFile## saveMyAppFileToCloudStorage Error: ' + e.toString()); //ERROR COMES FROM THIS LINE
return false;
}
return true;
}
I assume you're using the package ffmpeg_kit_flutter.
First, why it's not working: execute and executeAsync return FFmpegSession objects. The run of FFmpeg doesn't need to be finished for these methods to complete. In fact, the returned session object has methods like getState to monitor whether the run of FFmpeg has completed.
A good way to fix this: The documentation for executeAsync has a hint for what to do here.
Note that this method returns immediately and does not wait the execution to complete. You must use an FFmpegSessionCompleteCallback if you want to be notified about the result.
You can set a completion callback by passing a function to executeAsync. Here's the full function signature from the docs:
Future<FFmpegSession> executeAsync(
String command,
[FFmpegSessionCompleteCallback? completeCallback = null,
LogCallback? logCallback = null,
StatisticsCallback? statisticsCallback = null]
)
FFmpegSessionCompleteCallback is just a function that accepts an FFmpegSession and returns nothing. You can provide your own.
void someCompletionFunction() {
setState(() {
currentMyAppFileFilename = currentMyAppFileFilename + '1.mp3';
});
}
await FFmpegKit.executeAsync(/*...parms...*/, someCompletionFunction);
Future vs callback: If you prefer to use Futures and async-await instead of callbacks, you'll need to create your own Future and update it in the callback. See Dart, how to create a future to return in your own functions? for an example.
Does anyone know how to get an argument pass by MethodChannel in windows?
Here is my code to send and receive data.
I need to get data value in string type
String data = "Some data";
await platform.invokeMethod("OpenViewer", {"data":data});
channel->SetMethodCallHandler([](const flutter::MethodCall<>& call, std::unique_ptr<flutter::MethodResult<>> result)
{
// check method name called from dart
if (call.method_name().compare("OpenViewer") == 0) {
}
else {
result->NotImplemented();
}
});
you could use something like below
if (method_call.method_name().compare("launch") == 0) {
std::string url = GetUrlArgument(method_call);
if (url.empty()) {
result->Error("argument_error", "No URL provided");
return;
}
std::optional<std::string> error = LaunchUrl(url);
if (error) {
result->Error("open_error", error.value());
return;
}
result->Success(EncodableValue(true));
For more read here from url_launcher
How can I get multiple messages from dart isolate?
I'm trying to create an excel file and want to do some operation on that file in an isolate. Before doing an operation on that file, I want to return an message to main isolate, that excel file is created.
Here is function goes in isolate :
foo(String filePath){
// create excel file
var bytes = File(filePath).readAsBytesSync();
var excel = Excel.decodeBytes(bytes);
//HERE I WANT TO SEND THE MESSAGE THAT CREATING EXCEL FILE IS DONE
// some operatoin on excel file
var result = doSomeOperation(excel);
return result;
}
Main isolate code :
var result = await compute(foo, filePath);
What should I do to get creating file message before the actual result comes?
For excel, I'm using excel: ^2.0.0-null-safety-3 package.
Compute only returns one result. If you want to pass multiple 'events' back to the main isolate then you need to use the full Isolate logic (with sendPort and receivePort).
For example, the following code runs in an isolate, and downloads a file while emitting float values to represent progress, potentially a String to indicate log messages and then a bool to indicate success or failure upon completion.
Future<void> isolateDownload(
DownloadRequest request) async {
final sendPort = request.sendPort;
if (sendPort != null) {
var success = false;
var errorMessage = '';
var url = Uri.parse('a_url_based_on_request');
IOSink? out;
try {
http.StreamedResponse response =
await http.Client().send(http.Request('GET', url));
if (response.statusCode == 200) {
var filePath =
join(request.destinationDirPath, '${request.fileName}.ZIP');
var contentLength = response.contentLength;
var bytesLoadedUpdateInterval = (contentLength ?? 0) / 50;
var bytesLoaded = 0;
var bytesLoadedAtLastUpdate = 0;
out = File(filePath).openWrite();
await response.stream.forEach((chunk) {
out?.add(chunk);
bytesLoaded += chunk.length;
// update if enough bytes have passed since last update
if (contentLength != null &&
bytesLoaded - bytesLoadedAtLastUpdate >
bytesLoadedUpdateInterval) {
sendPort.send(bytesLoaded / contentLength);
bytesLoadedAtLastUpdate = bytesLoaded;
}
});
success = true;
if (contentLength != null) {
sendPort.send(1.0); // send 100% downloaded message
}
} else {
errorMessage =
'Download of ${request.fileName} '
'received response ${response.statusCode} - ${response.reasonPhrase}';
}
} catch (e) {
errorMessage = 'Download of ${request.chartType}:${request.chartName} '
'received error $e';
} finally {
await out?.flush();
await out?.close();
if (errorMessage.isNotEmpty) {
sendPort.send(errorMessage);
}
sendPort.send(success);
}
}
}
The code that spawns the isolate then simply checks for the type of the message passed to it to determine the action.
Future<bool> _downloadInBackground(
DownloadRequest request) async {
var receivePort = ReceivePort();
request.sendPort = receivePort.sendPort;
var isDone = Completer();
var success = false;
receivePort.listen((message) {
if (message is double) {
showUpdate(message);
}
if (message is String) {
log.fine(message); // log error messages
}
if (message is bool) {
success = message; // end with success or failure
receivePort.close();
}
}, onDone: () => isDone.complete()); // wraps up
await Isolate.spawn(isolateDownload, request);
await isDone.future;
return success;
}
I have the following method which is use dto verify a ticket/token
var ticketArray = ticket.split('|');
//First check to verify token using simple versification algo
if (widget.eventID.toString() != (ticketArray[0])) {
setState(() {
ticketMainMsg = 'This QR code is NOT VALID';
ticketsubtitle = ticketArray.length != 2
? 'The QR code is fake'
: 'QR code could belong to another event';
ticketStatus = false;
return;
});
}
//Make API call
ticketModel = HttpVerifyTicketPost(
eventId: widget.eventID,
ticket: ticket,
scannerId: widget.scannerId,
).verifyTicket();
}
From above, you can see I do a very simple check on the qr code/token if this simple step fails, I don't bother making an API call and I set the state based on these values.
However if the check passes, then I proceed to make an API call to the server to fully verify the token/code.
My issue is I am struggling to now assign the values from the API call to the ticketStatus, ticketMainMsgand ticketsubtitle parameters. Can anyone helo shed some light. I am quite new to flutter but I am aware that the TicketModel will be a type of Future. My background is PHP so forgive me!
EDIT: The httpVerifyTicket Class
class HttpVerifyTicketPost {
String ticket;
int someId;
int anotherId;
HttpVerifyTicketPost(
{required this.ticket, required this.someId, required this.anotherId});
String verifyURL =
'https://api.com/api/vendors/scanner/native/verify/ticket';
Future<TicketModel> verifyTicket() async {
var storage = await SharedPreferences.getInstance();
var code= storage.getString('code');
var client = http.Client();
var ticketModel = null;
var body = {
'ticket': ticket,
'scanner': scannerCode,
'someId': someId,
'anotherId': anotherId
};
try {
var url = Uri.parse(verifyURL);
var res = await client.post(url, body: jsonEncode(body));
if (res.statusCode == 200) {
var jsonString = res.body;
var jsonMap = json.decode(jsonString);
ticketModel = TicketModel.fromJson(jsonMap);
}
return ticketModel;
} catch (Exception) {
return ticketModel;
}
}
}
Try this please
HttpVerifyTicketPost(
eventId: widget.eventID,
ticket: ticket,
scannerId: widget.scannerId,
).verifyTicket().then((value){setState(() {
ticketModel=value
});
});
I don't quite understand what you want to achieve, but maybe you need to add an asynchronous method like
ticketModel = await HttpVerifyTicketPost( //add await eventId: widget.eventID, ticket: ticket, scannerId: widget.scannerId, ).verifyTicket();
and you must add async like Future Foo() async {your code...}