Develop Reference

Can I save the contents of an ObservableCollection so that the list is still intact when I restart my app?

What I want to do is have the user add items to the list. Then when they add an item I need the list to save, so that when the user closes the app and opens it again, the list they've created is still there.
Right now, I can add items to my list, but as soon as i close the app they will be gone.
private static ObservableCollection<ViewModels.ZoneViewModel> Zones = new ObservableCollection<ViewModels.ZoneViewModel>();
public void PopulateListView(string image, string name, string address)
{
if (name != "" && address != "")
{
Zones.Add(new ViewModels.ZoneViewModel { Image = image, Name = name, Address = address });
Application.Current.Properties["zoneslist"] = Zones;
}
}
protected override void OnAppearing()
{
if (Application.Current.Properties.ContainsKey("zoneslist"))
{
// Put the contents of the "zoneslist" key into a variable as a string.
var savedZones = Application.Current.Properties["zoneslist"] as ObservableCollection<ViewModels.ZoneViewModel>;
// Set the listviews' itemssource to the savedzones list.
zonesList.ItemsSource = savedZones;
}
}
Here's the code I use right now, I thought this could work to save it but that doesn't work.
EDIT: So I've tried what #Alessandro Calario suggested and after using json serialization the listview just gives me a ton of empty list items(even though i only added one). But an item is added and is saved, even when the app is closed. Progress, at least, but I'm not quite there yet. Anyone know a solution?
my code:
public void PopulateListView(string image, string name, string address)
{
if (name != "" && address != "")
{
Zones.Add(new ViewModels.ZoneViewModel { Image = image, Name = name, Address = address });
//Serialize to json string
var json = JsonConvert.SerializeObject(Zones);
Application.Current.Properties["zoneslist"] = json;
}
}
protected override void OnAppearing()
{
if (Application.Current.Properties.ContainsKey("zoneslist"))
{
// Put the contents of the "zoneslist" key into a variable as a string.
var savedZones = Application.Current.Properties["zoneslist"] as string; //ObservableCollection<ViewModels.ZoneViewModel>
JsonConvert.DeserializeObject<ObservableCollection<ViewModels.ZoneViewModel>>(savedZones);
// Set the listviews' itemssource to the savedzones list.
zonesList.ItemsSource = savedZones;
}
}

I think you can Serialize your List of Objects to a json String and save it to Application Properties

If using 3rd parties libraries is not a thing for your project I highly recommend you to use Akavache. This is an Async, persistent key-value store.
Once setup is very simple to use.
//To Insert your object
IObservable<Unit> InsertObject<T>(string key, T value, DateTimeOffset? absoluteExpiration = null);
//To Get your object
IObservable<T> GetObject<T>(string key);
where T can be your whole list.
Of course it's a little more than this but trust me just a little. Read the full documentation and hope it fits your needs.

The Application Properties only stores primitive types.
Note: the Properties dictionary can only serialize primitive types for
storage. Attempting to store other types (such as List can
fail silently).
Source: https://developer.xamarin.com/guides/xamarin-forms/application-fundamentals/application-class/
Either set it up so you are using the properties as a primitive storage, or go for another local storage mechanism such as Sqlite (a good guide here: https://developer.xamarin.com/guides/xamarin-forms/application-fundamentals/databases/)

Orchard: Why is my property not saved?

I'm working in the following Orchard code. For any reason, I can't get my property ProductsContent persisted on DB. I have rendered properly the text fields for it on the View, and created the migrations accordingly. The Leaves property of my Product part record is being stored properly, but my ProductsContent property is not.

Seems to me because you are using a viewmodel in your driver instead of the actual part, the part isn't updated automatically:
protected override DriverResult Editor(
ProductPart part,
IUpdateModel updater,
dynamic shapeHelper)
{
var model = new EditLeavesViewModel<ProductLeafEntry>();
if (updater.TryUpdateModel(model, Prefix, null, null))
{
// set the property manually here
part.ProductsContent = model.ProductsContent;
if (part.ContentItem.Id != 0)
{
_productService.UpdateLeavesForContentItem(
part.ContentItem, model.Leaves);
}
}
return Editor(part, shapeHelper);
}

Trying to eliminate redundant code execution for validation and entity

I'm looking to see if there is a way to eliminate one of the two calls that gets made to my method to google maps to calculate long/lat coordinates.
Here is my method.
public static GeocoderCoordinates GetCoordinates(string region)
{
WebRequest request = WebRequest.Create("http://maps.googleapis.com/maps/api/geocode/xml?sensor=false&address=" + HttpUtility.UrlEncode(region));
using (WebResponse response = request.GetResponse())
{
using (Stream stream = response.GetResponseStream())
{
XDocument document = XDocument.Load(new StreamReader(stream));
XElement longitudeElement = document.Descendants("lng").FirstOrDefault();
XElement latitudeElement = document.Descendants("lat").FirstOrDefault();
if (longitudeElement != null && latitudeElement != null)
{
return new GeocoderCoordinates
{
Longitude = Double.Parse(longitudeElement.Value, CultureInfo.InvariantCulture),
Latitude = Double.Parse(latitudeElement.Value, CultureInfo.InvariantCulture)
};
}
}
}
return null;
}
The first time I call this method it's for validation.
internal class ValidateLocationAttribute : ValidationAttribute
{
public override bool IsValid(object value)
{
var location = value as string;
GeocoderCoordinates coordinates = Geocoding.GetCoordinates(location);
if (coordinates == null)
return false;
return true;
}
}
and if there is no location that gets found it returns null - validation fails.
The second time it gets called is in the controller to set longitude/latitude coordinates within my entity.
[HttpPost]
public ActionResult Edit(EditStudentViewModel viewModel)
{
if (ModelState.IsValid)
{
Student student = studentRepository.Find(User.Identity.GetUserId());
if (student == null)
{
var newStudent = new Student
{
AspNetUserRefId = viewModel.AspNetUserRefId,
CatchPhrase = viewModel.CatchPhrase,
StartedPracticing = Convert.ToInt16(viewModel.SelectedYearId),
LocationPoints = Geocoding.GetDbGeography(viewModel.Location),
Location = viewModel.Location,
SO I'm running through this method twice just to insert/update a student. It seems a little redundant.
Isn't there a way to trigger/set validation state while the code in the controller is running, so I don't have to call this method twice (once for validation and once to set the actual values) when the user submits the form?
I thought about caching but don't think it's a good idea, unless someone can point out something.

If you think applying validation upfront using an attribute on the text box serve value to the user (early feedback), keep things as it is. Two calls is not too bad at all considering the value and cleanliness of the solution.
Second option is you can remove the attribute, and perform the validation in the controller action. If validation fails, display same form with all the same data but error message for the text box value (location). User will need to choose another location and then submit.
It is a trade off.
Important Tip: You can optimize your solution by storing region names in your DB and going to google API only if the region name does not present in your DB.

How can I keep my variable all the time without global variables?

I have two GridViews. I've got method GetGeneralDiagnosis which returns a list of all diagnosis:
CODE DIAGNOSIS
F50 Eating disorders
F51 Nonorganic sleep disorders
and method GetSpecificDiagnosis which returns more specific list:
CODE DIAGNOSIS
F50.0 Anorexia nervosa
F50.1 Atypical anorexia nervosa
F51.0 Nonorganic insomnia
F51.1 Nonorganic hypersomnia
Now I've got method which bind SPECIFIC DIAGNOSIS to second GridView according to GENERAL DIAGNOSIS from first GridView.
protected void gvGeneralDiagnosis_SelectedIndexChanged(object sender, EventArgs e)
{
string generalDiagnosis = gvGeneralDiagnosis.DataKeys[gvGeneralDiagnosis.SelectedIndex].Values["ICD10Code"].ToString();
var ICD10 = Visit.GetSpecificDiagnosis(); // here I'm getting data from database
gvSpecificDiagnosis.DataSource = ICD10.Where(i => i.ICD10Code.Contains(generalDiagnosis)).Select(i => new { i.ICD10Name, i.ICD10Code });
gvSpecificDiagnosis.DataBind();
}
I don't want to connect to database each time selected index is changed.
How can i get my list var ICD10 = Visit.GetSpecificDiagnosis() only once? I heard that global variables are very bad idea, so how can I do that in another way?

You can use a private member variable. This one "lives" as long as the class containing it lives. Wrap it with a property to access it and automatically read it from the database, if necessary.
private TypeOfICD10 _icd10;
private TypeOfICD10 ICD10
{
get
{
if (_icd10 == null) { // Get from database.
_icd10 = Visit.GetSpecificDiagnosis();
}
return _icd10;
}
}
Now you can use it like this and it will be read from the db only at the first call
protected void gvGeneralDiagnosis_SelectedIndexChanged(object sender, EventArgs e)
{
string generalDiagnosis = gvGeneralDiagnosis.DataKeys[gvGeneralDiagnosis.SelectedIndex].Values["ICD10Name"].ToString();
gvSpecificDiagnosis.DataSource = ICD10
.Where(i => i.ICD10Code.Contains(generalDiagnosis))
.Select(i => new { i.ICD10Name, i.ICD10Code });
gvSpecificDiagnosis.DataBind();
}

You can have your Visit class cache the returned data.
When GetSpecificDiagnosis is called, it will check whether this data was already retrieved from the database, and return it if it was. If it wasn't, it'll retrieve it from the database and save it to its cache.
One thing you should pay attention to is whether this data is static (i.e. never changes throughout the application's lifetime) or is it dynamic. In the first case, you won't have to do any special handling, but if it's the latter, you'll have to invalidate the cache one the information in the database has changed.
I recommend you to have a look here to see how to get started with caching in ASP.NET.

I don't know much about the Visist class from your question but why not cache ICD10 this way you will be using the cached object and the Database call will made only if the Cache Key ICD10 has a value of null
Example :
if(Cache["ICD10"] == null)
{
var ICD10 = Visit.GetSpecificDiagnosis();
Cache["ICD10"] = ICD10;
}
else
{
var ICD10 = Cache["ICD10"];
}

Check Validity for a QueryString using Entity Framework

I use C# Asp.Net and EF 4.
I have a scenario like MasterPage and DetailsPage.
So from my MasterPage I pass a variable as a QeryString to the DetailsPage, the DetailsPage will show up details for a specifc item in my DataBase.
I need to check the validity for my QueryString, in details I need:
Check if is Null, Empty or White Spaces.
Check if is NOT of type INT (just numbers not any letters).
Check if the Object NOT exists in my DB.
In case if Check result True, I will redirect the User.
At the moment I wrote this script. It is works but I would like to know if you know a better approch/code to solve this.
Also I would like to know if make sense to have this logic on every time the page Load, or would be enought us just on !Page.IsPostBack.
Thanks once again for your support guys!
protected void Page_Load(object sender, EventArgs e)
{
#region Logic Check Query String.
// Query String is Null or Empty.
if (string.IsNullOrWhiteSpace(ImageIdFromUrl))
RedirectToPage();
// Query String is not valid Type of INT.
int ImageId;
bool isInt = Int32.TryParse(ImageIdFromUrl, out ImageId);
if (isInt)
{
// Check if a valid Object request exist in Data Source.
using (CmsConnectionStringEntityDataModel context = new CmsConnectionStringEntityDataModel())
{
if (!context.CmsImagesContents.Any(x => x.ImageContentId == ImageId))
{
RedirectToPage();
}
}
}
else
RedirectToPage();
#endregion
}

You don't need to check it on every postback, only on a full page load. The query string is not sent to the server on postbacks.
I suggest you move all the query string validation logic to separate functions.