I am busy writing an application where the user needs to capture a lot of images and then they get packaged together with some text data and then they get uploaded to a local server. I want to implement the uploading on the Android platform through an Intent Service but I cannot find a good Xamarin Forms PCL example to show me how.
This is the method where I initialize the Intent to pass to the IntentService:
public async Task<bool> UploadAsync(Uri serviceAddress,
CaptureEntity capture,
List<ImageEntity> images)
{
try
{
Intent uploadIntent = new Intent();
uploadIntent.PutExtra("serviceAddress", serviceAddress.ToString());
uploadIntent.PutExtra("captureId", capture.WorkflowId.ToString());
StartService(uploadIntent);
return true;
}
catch (Exception exc)
{
App.logger.LogError(DateTime.Now, "Uploader", exc.ToString());
throw exc;
}
}
And this is the IntentService itself.
[Service]
public class ServiceIntent : IntentService
{
public ServiceIntent() : base("ServiceIntent")
{
}
//[return: GeneratedEnum]
public override StartCommandResult OnStartCommand(Intent intent, [GeneratedEnum] StartCommandFlags flags, int startId)
{
return base.OnStartCommand(intent, flags, startId);
}
public override void OnCreate()
{
base.OnCreate();
}
protected override void OnHandleIntent(Intent intent)
{
Uri serviceAddress = new Uri(intent.GetStringExtra("serviceAddress"));
Guid captureId = Guid.Parse(intent.GetStringExtra("captureId"));
CaptureEntity capture = new DatabaseConnection_Android().CreateConnection().Query<CaptureEntity>("SELECT * FROM [CaptureEntity]").Single(c => c.WorkflowId == captureId);
var images = new DatabaseConnection_Android().CreateConnection().Query<ImageEntity>("SELECT * FROM [ImageEntity]").Where(i => i.CaptureEntityId == capture.Id);
try
{
MultipartFormDataContent content = new MultipartFormDataContent();
StringContent strContent = new StringContent(
capture.XmlData,
Encoding.UTF8,
"text/xml");
IImageHandler handler = new ImageHandler_Droid();
HttpRequestMessage request = new HttpRequestMessage();
request.Headers.Add("workflow", capture.WorkflowId.ToString());
request.Method = HttpMethod.Post;
request.RequestUri = serviceAddress;
foreach (var image in images)
{
byte[] imageByte = handler.ReadAllBytes(image.ImagePath);
ByteArrayContent byteContent = new ByteArrayContent(imageByte);
byteContent.Headers.Add("Content-Type", "image/jpeg");
content.Add(byteContent, "file", image.ImageName);
}
content.Add(strContent, "text/xml");
request.Content = content;
using (HttpClient client = new HttpClient())
{
client.Timeout = TimeSpan.FromSeconds(180);
var response = client.SendAsync(
request,
HttpCompletionOption.ResponseContentRead).Result;
var readResponse = response.Content.ReadAsStringAsync().Result;
if (readResponse == "File uploaded.")
MessagingCenter.Send<CaptureEntity, string>(
capture,
"Completed",
"Success");
else if (readResponse.Contains("An error has occurred."))
MessagingCenter.Send<CaptureEntity, string>(
capture,
"Uploader",
String.Format(CultureInfo.InvariantCulture,
"Failed: {0}",
readResponse));
else
MessagingCenter.Send<CaptureEntity, string>(
capture,
"Uploader",
String.Format(CultureInfo.InvariantCulture,
"Failed: {0}",
readResponse));
}
}
catch (WebException webExc)
{
MessagingCenter.Send<string, string>("Uploader", "Failed",
String.Format(CultureInfo.InvariantCulture,
"{0} upload failed.\n{1}",
capture.DisplayName,
webExc.Message));
}
catch (TimeoutException timeExc)
{
MessagingCenter.Send<string, string>("Uploader", "Failed",
String.Format(CultureInfo.InvariantCulture,
"{0} upload failed.\n{1}",
capture.DisplayName,
timeExc.Message));
}
catch (Exception exc)
{
MessagingCenter.Send<string, string>("Uploader", "Failed",
String.Format(CultureInfo.InvariantCulture,
"{0} upload failed.\n{1}",
capture.DisplayName,
exc.Message));
}
}
}
Can anyone tell me what I am doing wrong as I am getting the following error when I want to start the service:
Java.Lang.NullPointerException: Attempt to invoke virtual method 'android.content.ComponentName android.content.Context.startService(android.content.Intent)' on a null object reference
In your Intent declaration you need to tell the service you want to call
Something like this:
var uploadIntent = new Intent(this, typeof(ServiceIntent));
Note: this represents the Context.
Update:
As mentioned in the comments your interface implementation cannot derive from Activity class. In order to have access to the Context to be able to call the StartService method and also create your Intent you can make it in two ways:
Using the Xamarin.Forms.Forms.Context:
public async Task<bool> UploadAsync(Uri serviceAddress,
CaptureEntity capture,
List<ImageEntity> images)
{
try
{
var context = Xamarin.Forms.Forms.Context;
var uploadIntent = new Intent(context, typeof(ServiceIntent));
uploadIntent.PutExtra("serviceAddress", serviceAddress.ToString());
uploadIntent.PutExtra("captureId", capture.WorkflowId.ToString());
context.StartService(uploadIntent);
return true;
}
catch (Exception exc)
{
App.logger.LogError(DateTime.Now, "Uploader", exc.ToString());
throw exc;
}
}
If you are using latest versions of Xamarin.Forms this global context was deprecated and they suggest to you local context instead. You can still use it though but in future updates of XF your app might break.
using CurrentActivity plugin:
public async Task<bool> UploadAsync(Uri serviceAddress,
CaptureEntity capture,
List<ImageEntity> images)
{
try
{
var context = CrossCurrentActivity.Current.Activity;
var uploadIntent = new Intent(context, typeof(ServiceIntent));
uploadIntent.PutExtra("serviceAddress", serviceAddress.ToString());
uploadIntent.PutExtra("captureId", capture.WorkflowId.ToString());
context.StartService(uploadIntent);
return true;
}
catch (Exception exc)
{
App.logger.LogError(DateTime.Now, "Uploader", exc.ToString());
throw exc;
}
}
This plugin can be installed from nugget and the setup is very straight forward. Basically it gives you access to the current activity and you can use it as your context to call the IntentService
Hope this helps.-
Here is the IntentService.
IntentService is a base class for Services that handle asynchronous requests (expressed as Intents) on demand. Clients send requests through startService(Intent) calls; the service is started as needed, handles each Intent in turn using a worker thread, and stops itself when it runs out of work.
In Android, we usually use IntentService to do asynchronous operator. As we all know, thread is also used to do asynchronous operator. The difference between IntentService and Thread is IntentService is Service which belongs to Android Component. So, the priority of IntentService is higher than Thread.
For example, there is a ActivityA which has a IntentService, and there is a ActivityB which has a Thread, both IntentService and Thread are working, and both ActivityA and ActivityB are al background Activity. Now, if your phone's system doesn't have extra resources, your ActivityB will be killed firstly.
About the Exception:
Java.Lang.NullPointerException: Attempt to invoke virtual method 'android.content.ComponentName android.content.Context.startService(android.content.Intent)' on a null object reference
That means you should use android.content.Context to call the StartService method. In Android, there are three kinds of Context. Application, Activity and Service. So you can call the StartService method in these three classes directly. If you are not in these three classes, you need pass the Context to your class, and then use the Context to call StartService.
I added Activity for this class' inheritance.
If you do this, your class will be a Activity, and you need to register it in your manifiest, add layout for your class, and it should have the lifecycle, and etc. It will not be what you want to get class. In Android, Activity is a Component, not normal class, so you can't inherit it unless you want your class to be a Activity.
Demo:
I have made a demo for you,
My application is completely based on internet and it does not work without it, when the internet is not available or it is slow my application is getting stopped unfortunately.
I tried to implement try, catch but it is not helping me out as it is not throwing any exception, then I thought that I have to check the internet connectivity continuously till the app is running and stop any activity from performing and set a popup to connect to the internet.
I am able to get the popup whenever I call a method which has the following code inside it,
ConnectivityManager connectivityManager = (ConnectivityManager)GetSystemService(ConnectivityService);
NetworkInfo networkInfo = connectivityManager.ActiveNetworkInfo;
if (networkInfo == null)
{
AlertDialog.Builder alert = new AlertDialog.Builder(this);
alert.SetTitle("Network");
alert.SetMessage("Please turn of your Wifi or Mobile Data From Settings");
alert.SetPositiveButton("OK", (senderAlert, args) => {
Intent intent = new Intent(Android.Provider.Settings.ActionSettings);
StartActivity(intent);
});
alert.SetNegativeButton("Cancel", (senderAlert, args) => {
Toast.MakeText(this, "Cancelled!", ToastLength.Short).Show();
Finish();
});
Dialog dialog = alert.Create();
dialog.Show();
But I am unable to get the connection checked continuously, So Can some one Please help me to complete get this functionality in my application.
You need to use a BroadcastReceiver to monitor network changes.
[BroadcastReceiver(Enabled = true)]
[IntentFilter(new[] { "android.net.conn.CONNECTIVITY_CHANGE" })]
[Android.Runtime.Preserve(AllMembers = true)]
public class ConnectivityChangeBroadcastReceiver : BroadcastReceiver
{
public override void OnReceive(Context context, Intent intent)
{
if (intent.Action != ConnectivityManager.ConnectivityAction)
return;
//Check if is connected and raise a custom event or store
//the current in a static global variable
}
}
}
In Android 7.0, you need to remove IntentFilter from the class and register the receiver.
var receiver = new ConnectivityChangeBroadcastReceiver();
Application.Context.RegisterReceiver(receiver, new IntentFilter(ConnectivityManager.ConnectivityAction));
Another option is to use the ConnectivityPlugin https://github.com/jamesmontemagno/ConnectivityPlugin , which is easier to use.
CrossConnectivity.Current.ConnectivityChanged += HandleConnectivityChanged;
void HandleConnectivityChanged (object sender, ConnectivityChangedEventArgs e)
{
// You can check the network status in
//e.IsConnected
}
Note that The ACCESS_NETWORK_STATE and ACCESS_WIFI_STATE permissions are required.
I am using Windows Phone to download a file with a WebClient. The DownloadProgressChanged event does not work. It fires only once, returning a value of "4923206" for DownloadProgressChangedEventArgs.BytesRecieved. My code is:
private void listBox1_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
WebClient wb = new WebClient();
wb.DownloadProgressChanged += wbchange;
wb.OpenReadAsync(new Uri("http://sohowww.nascom.nasa.gov/data/LATEST/current_eit_304small.gif"));
}
private void wbchange(object sender, DownloadProgressChangedEventArgs e)
{
MessageBox.Show(e.BytesReceived.ToString()); (obviously in the end I will not be showing a message at every change)
}
What is wrong with this?
It's working absolutely fine, it just happens to have downloaded all the bytes on the first DownloadProgressChanged invoke.
If you read the documentation you'll see that this is the expected behaviour.
I have wrote this code:
private void button1_Click(object sender, RoutedEventArgs e)
{
HttpWebRequest request = SendRequests.CreateRequest(serverTextBox.Text);
IAsyncResult result = request.BeginGetResponse(new AsyncCallback(ReadWebRequestCallback), request);
}
private void ReadWebRequestCallback(IAsyncResult callbackResult)
{
HttpWebRequest myRequest = (HttpWebRequest)callbackResult.AsyncState;
try
{
HttpWebResponse myResponse = (HttpWebResponse)myRequest.EndGetResponse(callbackResult);
using (StreamReader httpwebStreamReader = new StreamReader(myResponse.GetResponseStream()))
{
string results = httpwebStreamReader.ReadToEnd();
loginValue = Parser.ParseLoginValue(results);
}
myResponse.Close();
}
catch (WebException we)
{
//
}
}
My problem at this point is that after the Click on the button I need the return value (here loginValue) of the BeginGetResponse to go on with the execution of the application.
I know that this is against the entire sense of asynchronous calls, but, there's a way to wait for the results before going on with the main thread?
Unfortunately, you have answered your own question. On Windows Phone, there is no way to do a synchronous web call.
But you don't really need to. If there is really nothing for your user to do while waiting for the response from the web, slap up a translucent overlay with a progress bar (or even better, use the global progress bar in the system try) and abide.
By contrast, if you were waiting for a synchronous call from the internet to return (which on a mobile device could take a long time), the UI would be locked and the user would think the application had hung (which, technically, is true).
Asynchronicity is your friend. Play nice with it.
I am calling a web service in Windows Phone 7.
I have added a service reference to a web service (.asmx Service) with the Refrence name RS.
Then i am calling Service Like below:
Class AModel
{
public void CreateT()
{
RS.RSSoapClient objRS = new RSRSSoapClient();
objRS.Completed += new EventHandler<RS.CompletedEventArgs>(objRS_Completed);
objRSAsync();
}
private void objRS_Completed(object sender, EventCompletedEventArgs e)
{
string str = e.Result;
responseEventArgs = new ResponseEventArgs();
responseEventArgs.response = e.Result;
System.Windows.Deployment.Current.Dispatcher.BeginInvoke(responseEventHandler, responseEventArgs);
}
}
Class BViewModel
{
public void CreateT()
{
AModel objAModel = new AModel();
objAModel.CreateT();
objAModel .responseEventHandler += new ResponseEventHandler(objAModel_responseEventHandler);
}
private void objAModel_responseEventHandler(ResponseEventArgs e)
{
//doing some thing
System.Windows.Deployment.Current.Dispatcher.BeginInvoke(responseEventHandler, responseEventArgs);
}
}
Here my Main problem is: Here i want to use MVVM architecture, So i am calling the Service in Model(Class AModel) Layer here i am invoking a event to notify the ViewModel(BViewModel) and Invoking same event in ViewModel to notify the View(.xaml page). Because of these events My app performance is degraded (time taken to bind the response is heavy). So please guide if make any thing wrong in implementing the MVVM architecture.
Thanks in advance.
Let your ViewModel do the controlling. Put the calling of the web service in a service object, IMyService and have it return Dto(s). From the ViewModel call myService.GetThings(); then do with the results what is required. If you need to map, display or persist them.