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OnActivityResult() not being called when using a Camera intent?

I am trying to make a page (lets call it page #2) within my Xamarin.Android app that has a button, when you press on that button the camera app opens. Then you take a picture, accept the picture you took, and then you should be brought back to the page that originally had the camera button on it (page #2), and the image you took will be displayed there under the button.
The problem is that my overridden OnActivityResult() method never gets called after you accept the picture. You press the button, the camera app opens, you take a picture, accept the picture, the camera app closes and you are brought back to the page BEFORE the camera button page (so you're on page #1 now). I think the camera app itself is crashing? I am not sure how to find those logs. Sometimes a popup will show that says "Unfortunately, the camera has stopped." I am guessing that it is the way I am trying to save the photo taken to the phone itself? The only errors I have seen are within the device log, and occasionally it will throw a permission error saying I dont have access to write to the storage device on the phone, but I have the "write" permissions in the manifest file. I am targeting API 26.
Any ideas?
Here is the method for clicking the button:
private int PIC_REQUEST_CODE = 1;
private ImageView imageView;
private Java.IO.File image;
private void Button_Click(object sender, EventArgs e)
{
Intent takePictureIntent = new Intent(MediaStore.ActionImageCapture);
if (takePictureIntent.ResolveActivity(PackageManager) != null)
{
try
{
// Create an image file name
string timeStamp = DateTime.Now.ToString("yyyyMMdd_HHmmss");
string imageFileName = "JPEG_" + timeStamp + "_";
Java.IO.File storageDir = GetExternalFilesDir(global::Android.OS.Environment.DirectoryPictures);
Java.IO.File image = Java.IO.File.CreateTempFile(
imageFileName, /* prefix */
".jpg", /* suffix */
storageDir /* directory */
);
global::Android.Net.Uri photoURI = FileProvider.GetUriForFile(ApplicationContext, PackageName + ".fileprovider", image);
takePictureIntent.PutExtra(MediaStore.ExtraOutput, photoURI);
takePictureIntent.AddFlags(ActivityFlags.GrantWriteUriPermission);
StartActivityForResult(takePictureIntent, PIC_REQUEST_CODE);
}
catch (Exception ex)
{
//Not sure what to do, but here's a break point at least.
Toast.MakeText(this, "blah blah something went wrong", ToastLength.Short).Show();
}
}
}
And here is my simple OnActivityResult that gets skipped/ never called:
protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
{
if (requestCode == PIC_REQUEST_CODE && resultCode == Result.Ok)
{
Bitmap bitmap = (Bitmap)data.Extras.Get("data");
imageView.SetImageBitmap(bitmap);
}
}

I figured out the current issue of the OnActivityResult() not being called. At the top above the class I was declaring
[Activity(Label = "#string/page_name", ScreenOrientation = ScreenOrientation.Portrait, NoHistory = true)]
The important note here is the "NoHistory=True" apparently that makes the page exit and return back to the previous page. Deleting the "NoHistory=true" worked and made it so the OnActivityResult() gets called. Some documentation about it says "A value of 'true' means that the activity will not leave a historical trace. It will not remain in the activity stack for the task, so the user will not be able to return to it" so I guess that makes sense.

How can I pop a navigation page when a value changes in a static class?

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.

Reload Data every time I navigate to Page

I have this Windows Phone Page where I load data through the standard ViewModel scope.
public Profile()
{
InitializeComponent();
App.PersonalizedViewModel.favorites.Clear();
DataContext = App.PersonalizedViewModel;
this.Loaded += new RoutedEventHandler(MainPage_Loaded);
}
private void MainPage_Loaded(object sender, RoutedEventArgs e)
{
if (!App.PersonalizedViewModel.IsDataLoaded)
{
App.PersonalizedViewModel.LoadData();
}
}
This works fine. However when I navigate to this page from some other page the data is still the same. I mean the LoadData() method should recheck updated data right? Please suggest.
EDIT:
My PersonalizedViewModelClass:
public class PersonalizationViewModel: INotifyPropertyChanged
{
public PersonalizationViewModel()
{
this.favorites = new ObservableCollection<ItemViewModel>();
this.Bar = new ObservableCollection<Bars>();
}
public ObservableCollection<ItemViewModel> favorites { get; private set; }
public ObservableCollection<Bars> Bar { get; private set; }
private string _sampleProperty = "Sample Runtime Property Value";
public string SampleProperty
{
get
{
return _sampleProperty;
}
set
{
if (value != _sampleProperty)
{
_sampleProperty = value;
NotifyPropertyChanged("SampleProperty");
}
}
}
public bool IsDataLoaded
{
get;
private set;
}
/// <summary>
/// Creates and adds a few ItemViewModel objects into the Items collection.
/// </summary>
public async void LoadData()
{
favorites.Clear();
try
{
var query = ParseObject.GetQuery("Favorite")
.WhereEqualTo("user", ParseUser.CurrentUser.Username);
IEnumerable<ParseObject> results = await query.FindAsync();
this.favorites.Clear();
foreach (ParseObject result in results)
{
string venue = result.Get<string>("venue");
string address = result.Get<string>("address");
string likes = result.Get<string>("likes");
string price = result.Get<string>("price");
string contact = result.Get<string>("contact");
this.favorites.Add(new ItemViewModel { LineOne=venue, LineTwo=address, LineThree=likes, Rating="", Hours="", Contact=contact, Price=price, Latitude="", Longitude="" });
}
if (favorites.Count == 0)
{
// emailPanorama.DefaultItem = emailPanorama.Items[1];
MessageBox.Show("You do not have any saved cafes. Long press a cafe in main menu to save it.");
}
}
catch (Exception exc)
{
MessageBox.Show("Data could not be fetched!", "Error", MessageBoxButton.OK);
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(String propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (null != handler)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}
Implementation of PersonalizedViewModel:
protected async override void OnNavigatedTo(NavigationEventArgs e)
{
base.OnNavigatedTo(e);
await App.PersonalizedViewModel.LoadData();
user_tb.Text = ParseUser.CurrentUser.Username;
if (NavigationContext.QueryString.ContainsKey("item"))
{
var index = NavigationContext.QueryString["item"];
var indexParsed = int.Parse(index);
mypivot.SelectedIndex = indexParsed;
}
if (NavigationService.BackStack.Any())
{
var length = NavigationService.BackStack.Count() - 1;
var i = 0;
while (i < length)
{
NavigationService.RemoveBackEntry();
i++;
}
}
}

I don't see the problem, however, I think you need to narrow in on the problem.
First off, you are calling LoadData from 2 places. 1 from MainPage_Load and 1 from OnNavigatedTo. In MainPage_Load it is conditional and in OnNavigatedTo it is always being called. I suggest that you get to a single path through the code instead of 2 so that you don't get different experiences. I personally recommend (without knowing all the details) that you call load data from OnNavigatedTo instead of MainPage_Load. If you want to do it conditionally that is fine but if you are loading the data from memory, it really is unnecessary as you won't improve performance anymore than a few milliseconds. Also, if you are not loading from memory, you may not want to load it conditionally because the underlying data may have changed. In either case, the choice to load data or not should be moved out of the view and into the data layer (but that is for another post).
Once you have a single path chosen (i.e. calling LoadData from MainPage_Load or OnNavigatedTo) you should use your debugger. Put a break point in LoadData method and if it is being called appropriately, then your problem is more specific than your posted question. Here are some questions to think about (you may want to start from the last question and work your way backward)
Questions:
Is LoadData being called appropriately?
Does ParseObject have the correct data?
Is the ParseUser...UserName set properly?
Is the foreach being executed the proper # of times (i.e. does the result of your query have the right # of items?)
Couple Code Tips completely unrelated to this problem:
Single Path through code. Don't call LoadData from more than one place.
Don't call favorites.clear() twice in the same method. (it is called twice in LoadData)
Consistent naming. favorites is lowercase but Bar is upper case.
User proper data types. On your ItemViewModel you have Hours, Latitude, and Longitude. You have them as strings. These clearly are not strings. Also, you should not set them to empty. Empty means they have been set to a value. Emtpy is a valid value. Null means not set. To keep your objects clean and accurate you want to be accurate in how you set things and then deal appropriately with the impact. If you really really want them to be initialized to empty strings, then at least do it in the constructor of ItemViewModel so that every caller doesn't have to know how to initialize every property. I guarantee this is leading to buggy code if you continue using this practice.
Please take the comments as constructive criticism not criticism. I know many people don't like to hear these things but the teams I lead write bugs until they start following these types of guidelines.
Good luck,
Tom

Instead of defining this
App.PersonalizedViewModel.favorites.Clear();
DataContext = App.PersonalizedViewModel;
this.Loaded += new RoutedEventHandler(MainPage_Loaded);
into constructor i.e. Profile I would suggest remove this code from Constructor and add it into your OnNavigatedTo. so the data will load after navigation
Your OnNavigatedTo Method looks like follows
protected async override void OnNavigatedTo(NavigationEventArgs e)
{
base.OnNavigatedTo(e);
App.PersonalizedViewModel.favorites.Clear();
DataContext = App.PersonalizedViewModel;
this.Loaded += new RoutedEventHandler(MainPage_Loaded);
}
Might be your problem will solve.
Edit
Try this query
var results = (from find in ParseObject.GetQuery("Favorite").WhereEqualTo("user", ParseUser.CurrentUser.Username) select find);
Tried this:
var query = from favorite in ParseObject.GetQuery("Favorite")
where favorite.Get<string>("user") == ParseUser.CurrentUser.Username
select favorite;
IEnumerable<ParseObject> results = await query.FindAsync();

I had a similar Problem.All u want to do here is generate a new instance of the Page.U can do this in two Ways.
One Way is by forcing a GUID along with Page Navigation URI that will create a New Instance of the Page and your Load Data() will work.
NavigationService.Navigate(new Uri(String.Format("/MainPage.xaml?item={0}", Guid.NewGuid().ToString()), UriKind.RelativeOrAbsolute));
The Second Way to implement that Part of your Page in a User Control .Like create a User Control for Load Data() and put it in constructor.It will generate a new Instance everytime you load the Page.

If the problem persists in the front end,you can try this.
1.have you mentioned the below attribute in your xaml page?
<UserControl Loaded="MainPage_Loaded">
So that every time the page loads the data will get loaded on to the page.
2.The data must exist, if you have no problem in the code behind as it is a WPF application and not a web page.
Hope you find it useful.

Two changes required..
Remove the this.Loaded from OnNavigatedTo. That may not be required.
Second move the LoadData to OnNavigatedTo method
protected async override void OnNavigatedTo(NavigationEventArgs e)
{
base.OnNavigatedTo(e);
App.PersonalizedViewModel.favorites.Clear();
DataContext = App.PersonalizedViewModel;
// this.Loaded += new RoutedEventHandler(MainPage_Loaded);
if (!App.PersonalizedViewModel.IsDataLoaded)
{
App.PersonalizedViewModel.LoadData();
}
}
For the purpose of debugging, you can remove the line if (!App.PersonalizedViewModel.IsDataLoaded) and try.

Prepare data before go to the main view

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.

Windows Phone 8 Long List Selector - scroll to bottom after data loaded async

I'm creating an app similar to the stock Messaging. But i'm very new to wp8 development and also to c# and .net
I'm using the Long List Selector to display messages. Messages are loaded on NavigatedTo event of the page. the handler is async as it is loading the data from a webservice, when there are 0 stored in local db, then it saves them in local database.
I would like to scroll to the last message after the data is loaded.
the page OnNavigated to
protected override async void OnNavigatedTo(NavigationEventArgs e)
{
string contactId = "";
if (NavigationContext.QueryString.TryGetValue("contactId", out contactId))
{
await App.MessagesViewModel.LoadData();
DataContext = App.MessagesViewModel;
//scroll to last message, but it's apparently to soon
var lastMessage = App.MessagesViewModel.Messages.LastOrDefault();
llsMessages.ScrollTo(lastMessage);
}
}
but this throws an exception System.ArgumentException: The provided item doesn't exist in the collection. So i figured the list hasn't yet changed.
So i tried different events of LongListSelector that would indicate that it has already added the data from the view model. After a while of experimetnation i came up with this
private void llsMessages_SizeChanged(object sender, SizeChangedEventArgs e)
{
var lastMessage = App.MessagesViewModel.Messages.LastOrDefault();
if (lastMessage != null)
{
llsMessages.ScrollTo(lastMessage);
}
}
but this works only when the messages are loaded from the database. When loading from webservice the last message is null.
So after load i'm on the first message at top, then i navigate away from the page, then come back, the list scrolls to bottom. i would like to eliminate this, but i have no idea how.
is there any way how to accomplish this?

Maybe this will work:
private async Task DoAndScroll()
{
await App.MessagesViewModel.LoadData();
var lastMessage = App.MessagesViewModel.Messages.LastOrDefault();
llsMessages.ScrollTo(lastMessage);
}
protected override void OnNavigatedTo(NavigationEventArgs e)
{
string contactId = "";
if (NavigationContext.QueryString.TryGetValue("contactId", out contactId))
{
DataContext = App.MessagesViewModel;
DoAndScroll();
}
}

Try the ItemRealized event of the longlistselector. Check whether the currently processed item in the selector is the last item of your datacontext and if it is so, then scroll to that item. Below code worked for me.
private void longlist_ItemRealized(object sender, ItemRealizationEventArgs e)
{
Search.BindSearch search = e.Container.Content as Search.BindSearch;
if (search != null)
{
int offset = 0;
if (OCollectionBindSearch.Count - OCollectionBindSearch.IndexOf(search) <= offset)
{
longlist.ScrollTo(search);
}
}
}