i'm new to xamarin.forms development and i'm still having my first steps from the few tutorials that are found on the net.
I have an async task that returns the time from date.jsontest.com
and i have a timer that decrements a text in a label.
i want to put the async task in the timer so that it repeats itself and displays the time on the label however im getting cannot convert async lamba to func
here's my code please help me, thanks
static async Task<string> RequestTimeAsync()
{
using (var client = new HttpClient())
{
var jsonString = await client.GetStringAsync("http://date.jsontest.com/");
var jsonObject = JObject.Parse(jsonString);
return jsonObject["time"].Value<string>();
}
}
protected override async void OnAppearing()
{
base.OnAppearing();
timeLabel.Text = await RequestTimeAsync();
Device.StartTimer(TimeSpan.FromSeconds(1), () => { // i want the taks to be put
//here so that it gets repeated
var number = float.Parse(button.Text) - 1;
button.Text = number.ToString();
return number > 0;
});
}
Reloading the Content Page in the timer would do the trick, so if anybody can please help me it would be appreciated
You just need to wrap the async method call in a Task.Run(), for example:
Device.StartTimer(TimeSpan.FromSeconds(1), () =>
{
Task.Run(async () =>
{
var time = await RequestTimeAsync();
// do something with time...
});
return true;
});
Solved
as simple as that
private async void ContinuousWebRequest()
{
while (_keepPolling)
{
timeLabel.Text = "call: "+counter+" "+ await RequestTimeAsync()+Environment.NewLine;
// Update the UI (because of async/await magic, this is still in the UI thread!)
if (_keepPolling)
{
await Task.Delay(TimeSpan.FromSeconds(5));
}
}
}
static async Task<string> RequestTimeAsync()
{
using (var client = new HttpClient())
{
var jsonString = await client.GetStringAsync("http://date.jsontest.com/");
var jsonObject = JObject.Parse(jsonString);
TimePage.counter++;
return jsonObject["time"].Value<string>();
}
}
A simple clock demonstrates a one second timer action:
Device.StartTimer(TimeSpan.FromSeconds(1), doitt);
bool doitt()
{
label1.Text = DateTime.Now.ToString("h:mm:ss");
return true;
}
or you can try this:
static async Task<string> RequestTimeAsync()
{
using (var client = new HttpClient())
{
var jsonString = await client.GetStringAsync("http://date.jsontest.com/");
var jsonObject = JObject.Parse(jsonString);
return jsonObject["time"].Value<string>();
}
}
protected override async void OnAppearing()
{
base.OnAppearing();
var Text = await RequestTimeAsync();
Device.StartTimer(TimeSpan.FromSeconds(1), () => {
// i want the taks to be put
//here so that it gets repeated
var jsonDateTsk = RequestTimeAsync();
jsonDateTsk.Wait();
var jsonTime = jsonDateTsk.Result;
var number = float.Parse(Text) - 1;
var btnText = $"{number}";
return number > 0;
});
}
Related
I have app(net4.7.2) like this:
Program is simple, when user presses OK, im sending request to steam market to get informations about item which user entered (item steam market url) to textbox.
But when im trying to send request, first click event of button not working:
private void btnOK_Click(object sender, EventArgs e)
{
if (txtItemURL.Text.StartsWith("https://steamcommunity.com/market/listings/730/") == true)
{
Helpers.Helper.BuildURL(txtItemURL.Text);
SteamMarketItem SMI = Helpers.Helper.GetItemDetails();
lblPrice.Text = SMI.LowestPrice.ToString() + "$";
pbItemImage.ImageLocation = SMI.ImagePath;
Helpers.Helper.Kontrollar_BerpaEt();
}
else
{
Helpers.Helper.Kontrollar_SifirlaYanlisDaxilEdilib();
}
}
Method GetItemDetails():
public static SteamMarketItem GetItemDetails()
{
WinForms.Control.CheckForIllegalCrossThreadCalls = false;
Task.Run(() =>
{
try
{
using (HttpClient client = new HttpClient())
{
JavaScriptSerializer serializer = new JavaScriptSerializer();
/* Get item info: */
var ResultFromEndpoint1 = client.GetAsync(ReadyEndpointURL1).Result;
var Json1 = ResultFromEndpoint1.Content.ReadAsStringAsync().Result;
dynamic item = serializer.Deserialize<object>(Json1);
marketItem.LowestPrice = float.Parse(((string)item["lowest_price"]).Replace("$", "").Replace(".", ","));
/* Get item image: */
var ResultFromEndpoint2 = client.GetAsync(ReadyEndPointURL2).Result;
var Json2 = ResultFromEndpoint2.Content.ReadAsStringAsync().Result;
var html = ((dynamic)serializer.Deserialize<object>(Json2))["results_html"];
HtmlDocument htmlDoc = new HtmlDocument();
htmlDoc.LoadHtml(html);
marketItem.ImagePath = htmlDoc.DocumentNode.SelectSingleNode("//img[#class='market_listing_item_img']").Attributes["src"].Value + ".png";
Kontrollar_BerpaEt();
}
}
catch
{
Kontrollar_SifirlaYanlisDaxilEdilib();
}
});
return marketItem;
}
Class SteamMarketItem:
public class SteamMarketItem
{
public string ImagePath { get; set; }
public float LowestPrice { get; set; }
}
When im using Task.Run() first click not working, without Task.Run() working + but main UI thread stopping when request not finished.
I have no idea why this happens, I cant find problem fix myself, I will be glad to get help from you. Thanks.
If you want to use async you need to change your event handler to async so you can use await, please see the following:
1. Change your Event handler to async void, async void is acceptable on event handler methods, you should try to use async Task in place of async void in most other cases, so change your method signature to the following:
private async void btnOK_Click(object sender, EventArgs e)
{
if (txtItemURL.Text.StartsWith("https://steamcommunity.com/market/listings/730/") == true)
{
Helpers.Helper.BuildURL(txtItemURL.Text);
//here we use await to await the task
SteamMarketItem SMI = await Helpers.Helper.GetItemDetails();
lblPrice.Text = SMI.LowestPrice.ToString() + "$";
pbItemImage.ImageLocation = SMI.ImagePath;
Helpers.Helper.Kontrollar_BerpaEt();
}
else
{
Helpers.Helper.Kontrollar_SifirlaYanlisDaxilEdilib();
}
}
2. You shouldn't need to use Task.Run, HttpClient exposes async methods and you can make the method async, also, calling .Result to block on an async method is typically not a good idea and you should make the enclosing method async so you can utilize await:
//Change signature to async and return a Task<T>
public async static Task<SteamMarketItem> GetItemDetails()
{
WinForms.Control.CheckForIllegalCrossThreadCalls = false;
//what is marketItem?? Where is it declared?
try
{
using (HttpClient client = new HttpClient())
{
JavaScriptSerializer serializer = new JavaScriptSerializer();
/* Get item info: */
var ResultFromEndpoint1 = await client.GetAsync(ReadyEndpointURL1);
var Json1 = await ResultFromEndpoint1.Content.ReadAsStringAsync();
dynamic item = serializer.Deserialize<object>(Json1);
marketItem.LowestPrice = float.Parse(((string)item["lowest_price"]).Replace("$", "").Replace(".", ","));
/* Get item image: */
var ResultFromEndpoint2 = await client.GetAsync(ReadyEndPointURL2);
var Json2 = await ResultFromEndpoint2.Content.ReadAsStringAsync();
var html = ((dynamic)serializer.Deserialize<object>(Json2))["results_html"];
HtmlDocument htmlDoc = new HtmlDocument();
htmlDoc.LoadHtml(html);
marketItem.ImagePath = htmlDoc.DocumentNode.SelectSingleNode("//img[#class='market_listing_item_img']").Attributes["src"].Value + ".png";
Kontrollar_BerpaEt();
}
}
catch
{
Kontrollar_SifirlaYanlisDaxilEdilib();
}
//what is marketItem?? Where is it declared?
return marketItem;
}
I have a class constructor in the form:
protected LoginFunctions(){…..}
Within this function I call an async function using :
var tsk = Task.Run(async () => await PrePopulateLogin());
my trouble is that the PrePopulateLogin function is still being run when the constructor is exited. How can I change my code so that the constructor doesn't exit until after PrePopulateLogin has finished?
The PrePopulateLogin has to be async.
private async Task PrePopulateLogin()
{
var vector = await JSRuntime.Current.InvokeAsync<string>("blazorExtensions.ReadCookie", "vector");
var secureNextLogon = await JSRuntime.Current.InvokeAsync<string>("blazorExtensions.ReadCookie", "SecureNextLogon");
if (secureNextLogon != null)
{
var encryptor = new AesEncryptor(SecurityConstants.SecurityKey, Convert.FromBase64String(vector));
var decryptedValue = encryptor.Decrypt(secureNextLogon);
var email = decryptedValue.Split(' ')[0].Substring(6);
var password = decryptedValue.Split(' ')[1].Substring(9);
var rememberMe = decryptedValue.Split(' ')[2].Substring(11);
if (rememberMe == "True")
{
UserModel.EmailAddress = email;
UserModel.Password = password;
UserModel.RememberUser = true;
}
}
}
Finally found how to do it with Blazor.
I needed to remove the call from the constructor and instead override the BlazorComponents initializer event thus:
protected override async Task OnInitAsync()
{
await PrePopulateLogin();
}
First of all, sorry because I am so new at C# and I decided to make this question because I have been choked in this for hours.
I have an GUI that works with Google Cloud Speech services and make a Speech-to-Text operation. I share with you the whole method that runs when a button is clicked:
private async Task<object> StreamingMicRecognizeAsync(int seconds)
{
if (NAudio.Wave.WaveIn.DeviceCount < 1)
{
Console.WriteLine("No microphone!");
return -1;
}
GoogleCredential googleCredential;
using (Stream m = new FileStream(#"..\..\credentials.json", FileMode.Open))
googleCredential = GoogleCredential.FromStream(m);
var channel = new Grpc.Core.Channel(SpeechClient.DefaultEndpoint.Host,
googleCredential.ToChannelCredentials());
var speech = SpeechClient.Create(channel);
var streamingCall = speech.StreamingRecognize();
// Write the initial request with the config.
await streamingCall.WriteAsync(
new StreamingRecognizeRequest()
{
StreamingConfig = new StreamingRecognitionConfig()
{
Config = new RecognitionConfig()
{
Encoding =
RecognitionConfig.Types.AudioEncoding.Linear16,
SampleRateHertz = 48000,
LanguageCode = "es-ES",
},
InterimResults = true,
}
});
// Read from the microphone and stream to API.
object writeLock = new object();
bool writeMore = true;
var waveIn = new NAudio.Wave.WaveInEvent();
waveIn.DeviceNumber = 0;
waveIn.WaveFormat = new NAudio.Wave.WaveFormat(48000, 1);
waveIn.DataAvailable +=
(object sender, NAudio.Wave.WaveInEventArgs args) =>
{
lock (writeLock)
{
if (!writeMore) return;
streamingCall.WriteAsync(
new StreamingRecognizeRequest()
{
AudioContent = Google.Protobuf.ByteString
.CopyFrom(args.Buffer, 0, args.BytesRecorded)
}).Wait();
}
};
// Print responses as they arrive.
Task printResponses = Task.Run(async () =>
{
while (await streamingCall.ResponseStream.MoveNext(default(CancellationToken)))
{
foreach (var result in streamingCall.ResponseStream
.Current.Results)
{
foreach (var alternative in result.Alternatives)
{
Console.WriteLine(alternative.Transcript);
//Textbox1.Text = alternative.Transcript;
}
}
}
});
waveIn.StartRecording();
Console.WriteLine("Speak now.");
Result_Tone.Text = "Speak now:\n\n";
await Task.Delay(TimeSpan.FromSeconds(seconds));
// Stop recording and shut down.
waveIn.StopRecording();
lock (writeLock) writeMore = false;
await streamingCall.WriteCompleteAsync();
await printResponses;
return 0;
}
My problem is that I want to update the content of the Textbox1control but it doesn´t work. It writes perfectly the output into the console with the line Console.WriteLine(alternative.Transcript); but not into my textbox.
If someone could help I would appreciate so much his help.
The problem is that you're using Task.Run, which means your code will be running on a thread-pool thread.
Instead of calling Task.Run(), just move that code into a separate async method:
async Task DisplayResponses(IAsyncEnumerator<StreamingRecognizeResponse> responses)
{
while (await responses.MoveNext(default(CancellationToken)))
{
foreach (var result in responses.Current.Results)
{
foreach (var alternative in result.Alternatives)
{
Textbox1.Text = alternative.Transcript;
}
}
}
}
Then call that method directly (without Task.Run) from code that's already on the UI thread (e.g. an event handler).
The async machinery will make sure that after the await expression, you're back on the UI thread (the same synchronization context). So the assignment to the Text property will occur on the UI thread, and all should be well.
For example:
// This would be registered as the event handler for a button
void HandleButtonClick(object sender, EventArgs e)
{
var stream = client.StreamingRecognize();
// Send the initial config request
await stream.WriteAsync(...);
// Presumably you want to send audio data...
StartSendingAudioData(stream);
await DisplayResponses(stream.ResponseStream);
}
Tasks run on seperate threads, so you must Invoke an action that will be performed on the control's thread
Textbox1.Invoke(new Action(() =>
{
Textbox1.Text= "";
}));
Edit: For WPF, I believe the equivalent is
Textbox1.Dispatcher.Invoke(new Action(() =>
{
Textbox1.Text= "";
}));
have you tried using Dispatcher.InvokeASync()?
await Dispatcher.InvokeAsync(() => {while (await streamingCall.ResponseStream.MoveNext(default(CancellationToken)))
{
foreach (var result in streamingCall.ResponseStream
.Current.Results)
{
foreach (var alternative in result.Alternatives)
{
Textbox1.Text = alternative.Transcript;
}
}
}});
I can successfully play sounds using Xamarin forms (Android and iOS) however I also need to achieve the following:
I need to await so that if multiple sounds are 'played', one will complete before the next.
I need to return a boolean to indicate whether operation was a success.
Here is my current simplified code (for the iOS platform):
public Task<bool> PlayAudioTask(string fileName)
{
var tcs = new TaskCompletionSource<bool>();
string filePath = NSBundle.MainBundle.PathForResource(
Path.GetFileNameWithoutExtension(fileName), Path.GetExtension(fileName));
var url = NSUrl.FromString(filePath);
var _player = AVAudioPlayer.FromUrl(url);
_player.FinishedPlaying += (object sender, AVStatusEventArgs e) =>
{
_player = null;
tcs.SetResult(true);
};
_player.Play();
return tcs.Task;
}
To test the method, I have tried calling it like so:
var res1 = await _audioService.PlayAudioTask("file1");
var res2 = await _audioService.PlayAudioTask("file2");
var res3 = await _audioService.PlayAudioTask("file3");
I had hoped to hear the audio for file1, then file2, then file3. However I only hear file 1 and the code doesn't seem to reach the second await.
Thankyou
I think your issue here is that the AVAudioPlayer _player was being cleared out before it was finished. If you were to add debugging to your FinsihedPlaying, you'll notice that you never hit that point.
Try these changes out, I made a private AVAudioPlayer to sit outside of the Task
(I used the following guide as a reference https://developer.xamarin.com/recipes/ios/media/sound/avaudioplayer/)
public async void play()
{
System.Diagnostics.Debug.WriteLine("Play 1");
await PlayAudioTask("wave2.wav");
System.Diagnostics.Debug.WriteLine("Play 2");
await PlayAudioTask("wave2.wav");
System.Diagnostics.Debug.WriteLine("Play 3");
await PlayAudioTask("wave2.wav");
}
private AVAudioPlayer player; // Leave the player outside the Task
public Task<bool> PlayAudioTask(string fileName)
{
var tcs = new TaskCompletionSource<bool>();
// Any existing sound playing?
if (player != null)
{
//Stop and dispose of any sound
player.Stop();
player.Dispose();
}
string filePath = NSBundle.MainBundle.PathForResource(
Path.GetFileNameWithoutExtension(fileName), Path.GetExtension(fileName));
var url = NSUrl.FromString(filePath);
player = AVAudioPlayer.FromUrl(url);
player.FinishedPlaying += (object sender, AVStatusEventArgs e) =>
{
System.Diagnostics.Debug.WriteLine("DONE PLAYING");
player = null;
tcs.SetResult(true);
};
player.NumberOfLoops = 0;
System.Diagnostics.Debug.WriteLine("Start Playing");
player.Play();
return tcs.Task;
}
I have the following pieces of code:
private async void buttonStart_ItemClick(object sender, DevExpress.XtraBars.ItemClickEventArgs e)
{
Bot b = new Bot(_names);
var result = await b.Start(false, true, false);
MessageBox.Show("Done");
}
public async Task<bool> Start(bool instagram, bool twitter, bool xbox)
{
if (twitter)
{
Twitter t = new Twitter(Names);
await t.CheckNames();
}
return true;
}
public Task CheckNames()
{
List<Task> tasks = new List<Task>();
foreach (Name name in Names)
{
tasks.Add(Task.Factory.StartNew(async () =>
{
TwitterResponse result = await Check(name);
MessageBox.Show(result.msg);
}));
}
return Task.WhenAll(tasks);
}
public async Task<TwitterResponse> Check(Name name)
{
HttpClient http = new HttpClient();
HttpResponseMessage response = await http.GetAsync(string.Format("https://twitter.com/users/username_available?username={0}", name.Value));
string html = response.Content.ReadAsStringAsync().Result;
TwitterResponse result = new JavaScriptSerializer().Deserialize<TwitterResponse>(html);
return result;
}
However, I always seem to get the MessageBox saying "Done" before any of the tasks are completed.
Am I doing something wrong, how can I make sure all of the tasks actually complete before getting the messagebox?
The problem is the line tasks.Add(Task.Factory.StartNew(async () =>, you should almost never be using Task.Factory.StartNew and instead use Task.Run(.
The object that StartNew is returning is a Task<Task> which means it does not wait for the inner task to finish. You must either call .Unwrap() on the output of the StartNew before you add it to the collection or, much much better use Task.Run(
tasks.Add(Task.Run(async () =>
{
TwitterResponse result = await Check(name);
MessageBox.Show(result.msg);
}));
Which has a overload that takes in a Func<Task> and will unwrap the inner task for you.