I have created a C# WPF app. It takes an URL input from a text box and shows the downloaded html in another text box on a button click. To tell the user wait till the webpage is downloaded, I am appending text in the very beginning.
public void urlAnalyzer()
{
// Append text to Result box
Result.AppendText("Please wait, inspecting the URL.\n");
// Initiating WebClient to download webpage
WebClient inspecter = new WebClient();
// try-catch to avoid exception in a generic way
try
{
// stroring downloaded page in savedData
savedData = inspecter.DownloadString(webpage);
// appending downloaded html in Result box
Result.AppendText(savedData);
}
catch
{
Result.AppendText("You did not enter any valid URL.");
}
}
When the urlAnalyzer() is called, Result.AppendText() goes to Result text box's event handler method,
private void Result_TextChanged(object sender, TextChangedEventArgs e)
{
}
This event method is visited every time Result.AppendText() is called, but it doesn't append the string to Result box. When the urlAnalyzer() function is fully visited, texts then appear in the Result box.
How to make the appended text appear in the text box when the append statement is executed? How to update the text box on every text append call?
WebClient.DownloadString() is executed in UI thread and blocks UI updates. Use async version of download method:
public async void urlAnalyzer()
{
// Append text to Result box
Result.AppendText("Please wait, inspecting the URL.\n");
// Initiating WebClient to download webpage
WebClient inspecter = new WebClient();
// try-catch to avoid exception in a generic way
try
{
// stroring downloaded page in savedData
savedData = await inspecter.DownloadStringTaskAsync(webpage);
// appending downloaded html in Result box
Result.AppendText(savedData);
}
catch
{
Result.AppendText("You did not enter any valid URL.");
}
}
Related
So I have a bit of a weird problem.
I've implemented a camera preview class (largely following this code here: https://learn.microsoft.com/en-us/samples/xamarin/xamarin-forms-samples/customrenderers-view/) but have added a button at the bottom to take a picture. This involves the use of both some xamarin forms code and some xamarin android code.
However, the CapturePage is only put on the stack when the user announces that they want to take a photo, and after the photo has been taken, I want to pop the Capture page to go back to the main screen. Currently, I have a static boolean value in the overall project that is changed from false to true when a capture has occurred. Is there some way to get my code in Main.xaml.cs to wait on this value changing, then pop whatever is on top of the navigation stack? Is this a use for a property changed? See code below:
The code in Project.Droid that handles the capturing and saving of the image:
void OnCapButtonClicked(object sender, EventArgs e)
{
// capButton.capture is an instance of Android.Hardware.Camera
capButton.capture.TakePicture(null, null, this);
// stop the preview when the capture happens
CameraInfoContainer.isPreviewing = false;
}
public void OnPictureTaken(byte[] data, Camera camera)
{
var filepath = string.Empty;
var clientInstanceId = Guid.NewGuid().ToString();
var saveLoc = Android.OS.Environment.GetExternalStoragePublicDirectory(Android.OS.Environment.DirectoryPictures);
filepath = System.IO.Path.Combine(saveLoc.AbsolutePath, clientInstanceId + ".jpg");
try
{
System.IO.File.WriteAllBytes(filepath, data);
//mediascan adds the saved image into the gallery
var mediaScanIntent = new Intent(Intent.ActionMediaScannerScanFile);
mediaScanIntent.SetData(Android.Net.Uri.FromFile(new File(filepath)));
Forms.Context.SendBroadcast(mediaScanIntent);
}
catch (Exception e)
{
System.Console.WriteLine(e.ToString());
}
// CameraInfoContainer is a static class in Project NOT in Project.Droid
CameraInfoContainer.savedCapture = filepath;
CameraInfoContainer.capType = CaptureType.Photo;
CameraInfoContainer.captureComplete = true; // here is where I set the value (in Project)
}
Now the code in Project that pushes the capture page on the stack and that I want to trigger when the capture has happened:
// this method puts the capture page on the stack and starts the whole process
private async Task ExecuteNewCapture()
{
var cp = new CapturePage();
var np = new NavigationPage(cp);
await Navigation.PushModalAsync(np, true);
}
// this is the method that I want to trigger when a photo is taken (in Project/Main.xaml.cs)
private async Task Complete(string fileLoc)
{
await Navigation.PopModalAsync();
}
Answer is in a comment from Junior Jiang. Ended up using Xamarin.Forms.MessagingCenter to get done what I needed.
Working with Xamarin Android and C# -
I want to have a download function, that just download the next item (url) from the list if the first with index 0 is finished. While Downloading, the user should be able to extend the list (add new urls for download).
My idea was to have one void OnButtonClick() (for user input) and one custom aysnc void Download() function, as well the possibility to use the "share function" (intent) to send the link directly. It is working BUT only if the user does not uses the "share function" in another app (see here: Intent.GetStringExtra). If the App gets open via this intent, the download loop gets overwritten completely. Is there a way to avoid this "bug" or another solution for a download que?
protected override void OnCreate() //gets called if activity starts
{
string catchedLink = Intent.GetStringExtra(Intent.ExtraText);
if (!String.IsNullOrEmpty(catchedLink))
{
button.Text = catchedLink;
}
}
public OnButtonClick()
{
urlList.Add(Button.Text);
}
private aysnc void Download()
{
if(IsDownloading) return;
IsDownloading = true;
do
{
await DownloadSomethingFromTheInternet(); //Let's say these two function need 2 mins to complete -
await SafeItToStorage(); //But after one minute the user adds a secound url for download
//so this loop needs to run again (see below)
urlList.Remove(urlList[0]);
} while (urlList.Count >= 1) //see here
IsDownloading = false;
}
Please leave a comment if more details are needed.
Okay it's working now:
What I did:
Save the links on the device with Preferences.Set(); not only just with a List
Added LaunchMode = Android.Content.PM.LaunchMode.SingleTask to AndroidMainfest.xml (in <activity [...] />)
Used for intent-input following code:
protected override void OnNewIntent(Intent myIntent)
{
base.OnNewIntent(myIntent);
string catchedLink = myIntent.GetStringExtra(Intent.ExtraText);
if (!String.IsNullOrEmpty(catchedLink))
{
AddVideoToQue(catchedLink);
}
}```
Thanks #Leo Zhu - MSFT for his comments and help!
Im currently trying to create a messaging application from client to server. When the server sends the client a message it will open up an new form and add the text to a text box inside the form.
However the client is defiantly reviving the message, I tested this with a message box displaying the message before trying to update the text box. The text box is displaying the message perfectly.
However, when i try to edit the textboxt nothing happens. However my other method on a button click works perfectly. really unsure why this is happening.
I've also written an invoke method to check if the textbox need's to be invoked as i am using differen't threads for some methods.
Below is an example of my code with some screenshots the method below is being opened from another form "MAIN" i have reference to it in the code. Not sure if that is causing an issue perhaps?
public ChatWindow()
{
InitializeComponent();
Thread timerThread = new Thread(Main.ReceiveLoop);
timerThread.Start();
}
private void txtChatLog_TextChanged(object sender, EventArgs e)
{
}
private void btnSendMessage_Click(object sender, EventArgs e)
{
string clientReply = txtReply.Text;
string Message = "ClientMsg§" + clientReply;
var time = DateTime.Now;
txtChatWindow.AppendText($"{time} client: {clientReply}");
txtChatWindow.AppendText(Environment.NewLine);
Main main = new Main();
main.ChatResponse(Message);
txtReply.Text = "";
}
delegate void setTextCallBack(string message);
public void UpdateChatLog(string message)
{
if (txtChatWindow.InvokeRequired)
{
setTextCallBack d = new setTextCallBack(UpdateChatLog);
this.Invoke(d, new object[] { message });
}
else
{
var time = DateTime.Now;
string newMessage = message.Split('$')[1];
string messageToDisplay = $"{time} Server: {newMessage}";
MessageBox.Show(messageToDisplay);
this.txtChatWindow.AppendText(messageToDisplay);
this.txtChatWindow.AppendText(Environment.NewLine);
}
}
Below are some images of my server and the code running on the client:
as you can see the server is recieving what the client replies with, the textbox is also being appended for when the client presses the SEND button. However it isn't being changed when the method is called. You know the method is being called because the MessageBox.Show is being called and displaying what should be in the text box.
Really unsure what the issue is here. If anyone could help me It would be very appreciated! This is a project for my university degree that is due in soon!
Thankyou in advance!
When the user touch the app icon,
I want do these steps before user go to the main view
Fetch json string from URI
Use JArray.Parse to get the value
After all finish, go to the main view.
The problem is how can I prevent user to go to the main view
and put all the code
I tried to put it in Application_Launching method in the App.xaml.cs file
// Code to execute when the application is launching (eg, from Start)
// This code will not execute when the application is reactivated
private void Application_Launching(object sender, LaunchingEventArgs e)
{
// code here
}
But it doesn't prevent the program to go to the main view before the fetching finished.
And I found that actually in the MainPage.xaml, if I put this code like this
protected override void OnNavigatedTo(NavigationEventArgs e)
{
while(true) {}
// it will prevent the program to go to the main view,
// and will stick with the loading screen until this function reach its end
}
So I think, I can put the all the code here, when I finish the fetch, I will just break the while and it will go to the main view automatically.
And I try, this is the code
protected override void OnNavigatedTo(NavigationEventArgs e)
{
bool isFetchFinished = false;
ObservableCollection<PromoViewModel> Promos = new ObservableCollection<PromoViewModel>();
WebClient client = new WebClient();
client.DownloadStringCompleted += (s, evt) =>
{
if (evt.Error == null)
{
// Retrieve the JSON
string jsonString = evt.Result;
JArray promos = JArray.Parse(jsonString);
foreach (JObject promo in promos)
{
string name = promo["name"].Value<string>();
string description = promo["description"].Value<string>();
string img = promo["image"].Value<string>();
Promos.Add(new PromoViewModel() { Name = name, Description = description, Img = img });
}
isFetchFinished = true;
System.Diagnostics.Debug.WriteLine("finish fetch");
}
};
// run
client.DownloadStringAsync(new Uri("the json url"));
while(true) {
if(isFetchFinished) {
App.ViewModel.LoadData(Promos); // pass value to main view model
break; // after complete, break
}
}
}
I thought it would work, but it was not.
This is what I found,
The WebClient DownloadStringAsync won't run until the OnNavigatedTo function finished.
Because it's still waiting for the while loop to break and reach the end function.
And this
isFetchFinished = true; // will never executed
Resulting infinite loop.
I think I put the fetch code in the wrong method. Where is the right place to put all of this?
Ouch, you are doing it all wrong. First of all, you have to specify the starting page. If you want to download some data before navigating to it, you can create a special "download" page that is actually the first page navigated to when starting the application. And then, once the download is completed, you navigate to your main page. This is actually a replacement for the extended splash screen.
Also, never put while (true) in any UI code, that will simply freeze the application. Besides, if the application is frozen, you never get the chance to "unfreeze" it.
i want to use a background thread for the process of loading the XML data, possibly with a progress bar to let the user know that the application is actively doing something.
i have written this code through searching the net.
i want to load a XML tree in treeview on winform when a user cliks a Browse button.
In case of a large XML file the winform freezes.So to let the user know that in background the work is going on i want to add a progress bar.i have used a background worker here.
But it is raising an exception of System.ArgumentException showing this message "The URL cannot be empty.\r\nParameter name: url" on xmlDocument.Load(txtFileName.Text); this line.
My xml file is in correct format and is at the proper location where i selected.
But i am unable to find the cause of this exception.
Can you please help out or tell me the correction in my code?
Thanks....
private void btnBrowse_Click(object sender,EventArgs e)
{
bgWorker1.RunWorkerAsync();
StripProgressBar.Value = 0;
toolStripStatusLabel1.Text = "Browsing for a Xml file";
if (open.ShowDialog(this) == DialogResult.OK)
{
txtFileName.Text = open.FileName;
initiatingTree(open.FileName); //this variable gives the name of selected file
}
while (this.bgWorker1.IsBusy)
{
StripProgressBar.Increment(1);
// Keep UI messages moving, so the form remains
// responsive during the asynchronous operation.
Application.DoEvents();
}
}//Browse button
private void bgWorker1_DoWork(object sender, DoWorkEventArgs e)
{
xmlDocument = new XmlDocument();
Thread.Sleep(5000);
xmlDocument.Load(txtFileName.Text);
btnBrowse.Enabled = false;
}
private void bgworker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
// Set progress bar to 100% in case it's not already there.
StripProgressBar.Value = 100;
if (e.Error == null)
{
MessageBox.Show(xmlDocument.InnerXml, "Download Complete");
}
else
{
MessageBox.Show("Failed to download file");
}
// Enable the Browse button and reset the progress bar.
this.btnBrowse.Enabled = true;
StripProgressBar.Value = 0;
toolStripStatusLabel1.Text = "work finished processing request.";
}//workerCompleted
You're starting the asynchronous process immediately when the user clicks "Browse", by calling
bgWorker1.RunWorkerAsync();
This calls the DoWork method of your background worker, which sleeps for 5 seconds, and pulls the value from txtFileName.Text whether or not the user has completed their entry in the FileOpenDialog.
You'd be better off moving the byWorker1.RunWorkerAsync() (and the busy waiting) into the if (open.ShowDialog(this) == DialogResult.OK) block.
private void btnBrowse_Click(object sender,EventArgs e)
{
StripProgressBar.Value = 0;
toolStripStatusLabel1.Text = "Browsing for a Xml file";
if (open.ShowDialog(this) == DialogResult.OK)
{
txtFileName.Text = open.FileName;
initiatingTree(open.FileName);
bgWorker1.RunWorkerAsync();
while (this.bgWorker1.IsBusy)
{
StripProgressBar.Increment(1);
// Keep UI messages moving, so the form remains
// responsive during the asynchronous operation.
Application.DoEvents();
}
}
}
For these kinds of problems, it can be helpful to put a breakpoint right where the file is going to get loaded, and see what the value is when that happens... you might notice that it's getting called with an empty string.
You might also consider the version of RunWorkerAsync that takes a parameter; you could pass the file in that way, instead of trying to read it asynchronously from the textbox.
And personally, I wouldn't use a loop that calls Application.DoEvents(); instead I'd return control back to the UI thread and then Invoke() onto it from the asynchronous thread to effect the progressbar updates.
When the method bgWorker1.RunWorkerAsync(); is called the event DoWork is fired.
Because the method is called in the beginning of the application, the file name text box is empty.
I hope you've understood.