EDIT 2
I have got some help over the past few days on a problem that I am trying to work through. After receiving helpful support from several users, I have come across an error that I have been trying to fix over the weekend and still not succeeded.
I created a Dictionary, where I pass a string Country and also a ICollection of Places for that Country.
Dictionary<string, NewCountryClass> NTCD = new Dictionary<string, NewCountryClass>();
public void AddCountryCollection()
{
newCountryClass = new NewCountryClass(newCountry);
Collections.Add(newCountryClass);
NTCD.Add(newCountryClass.Country, newCountryClass);
}
public void AddPlace()
{
string Country = selectedItem.Country;
RenameQuestion(placeName);
NTCD[Country].Place.Add(placeName);
}
Here is my newCountryClass where I stored the Country and Places in that Country.
private ICollection<string> _places;
public ICollection<string> Places
{
get
{
return _places;
}
set
{
if (value == _places)
return;
_places = value;
RaisePropertyChanged(() => Places);
}
}
This is where the places could be added, but I create an instance of my class at the adding Country stage, and therefore can't pass a place at that time. (EDIT - I have moved the initialising of the collection into the constructor instead of in the Places property, as advised).
public NewCountryClass(string country)
{
_places = new ObservableCollection<string>();
if (country != null)
{
_country = country;
}
}
Therefore, I attempted to create a renamePlace() method:
public void RenamePlace(string place)
{
_places.Add(place);
}
However, _places still seems to be null even with this attempt. Any further ideas or anything I am doing wrong?
You need to learn how to debug a program. Basically, you try to instantiate your NewCountryClass here:
public void AddCountryCollection()
{ // <<< Put breakpoint here <<<
newCountryClass = new NewCountryClass(newCountry, placeName);
Collections.Add(newCountryClass);
NTCD.Add(newCountryClass.Country, newCountryClass);
}
If the placeName input parameter is null in the constructor, then it is also null here... you need to add a breakpoint here and find out why the value is null and ensure that it has a value by this stage in your program.
Would you not be better off initialising the _places collection in the constructor instead of the property get accessor?
public NewCountryClass(string country)
{
_places = new ObservableCollection<string>();
if (country != null)
{
_country = country;
}
}
Related
I am building xamarin forms app, I am using jamesmontemagno settings plugin and I'm adding a property which list of a class. But the thing is I'm not able to add or insert to the list, every time I use method Add or Insert it jump into the get not the set and I can't understand why.
here is my code and thanks for the help in advance:
//adding an item to the list
private void order(Sales_Order_Items sale)
{
orderlist.Add(sale);
Settings.Usercartlist.Add(sale);
}
I can only set it by using this code
Settings.Usercarlist=orderlist;
the property in the settings file
public static List<Sales_Order_Items> Usercartlist
{
set
{
string listValue = JsonConvert.SerializeObject(value);
AppSettings.AddOrUpdateValue(myIntListKey, listValue);
}
get
{
string value = AppSettings.GetValueOrDefault(myIntListKey, string.Empty);
List<Sales_Order_Items> myList;
if (string.IsNullOrEmpty(value))
myList = new List<Sales_Order_Items>();
else
myList = JsonConvert.DeserializeObject<List<Sales_Order_Items>>(value);
return myList;
}
}
When adding an item, the actual object reference does not change. Only the value changes. This is not picked up by the getter or setter.
The only way to update after each item is to add the line you already have: Settings.Usercarlist=orderlist; after each operation.
I am using like the following way you can try that
Ex.
private static UserDetails _currentUser = null;
public static UserDetails CurrentUser
{
get
{
if (_currentUser == null)
{
string data = AppSettings.GetValueOrDefault(nameof(CurrentUser), string.Empty);
if (data != null)
_currentUser = JsonConvert.DeserializeObject<LoginResponse>(data);
}
return _currentUser;
}
set
{
string data = JsonConvert.SerializeObject(value);
AppSettings.AddOrUpdateValue(nameof(CurrentUser), data);
_currentUser = value;
}
}
I see a lot of similar questions but none with a direct answer. I have a List<ClientEntry>. I want to access properties in ClientEntry. My code looks like this:
class ClientEntry
{
private string _clientName;
private string _clientEmail;
public void ClientEntry(string name, string email)
{
this._clientName = name;
this._clientEmail = email;
}
public string ClientName
{
get
{
return _clientName;
}
set
{
_clientName = value;
}
}
public string ClientEmail
{
get
{
return _clientEmail;
}
set
{
RegexUtilities Validator = new RegexUtilities();
if (Validator.IsValidEmail(value))
{
_clientEmail = value;
}
}
}
}
Later:
private List<ClientEntry> clientList;
I then add a bunch of ClientEntry's to the List.
How can I access the ClientName and ClientEmail properties for items in clientList? Also, how can I check for the existance of a certain ClientName or ClientEmail property within the List? Is this even possible with a list of objects? I know a dict would probably serve better, but I wanted to see if this could be done with a List and a class with properties.
You can use Linq to look for values inside of a list using Any()
Eg.
bool emailExists = clientList.Any(x=>x.ClientEmail == <email>);
To access values, you can use a index accessor if you know it, loop the collection, or use Where() to search it:
var email = clientList[index].ClientEmail
or
foreach (var client in clientList)
{
var email = client.ClientEmail
}
or
var email = clientList.Where(x=>x.ClientName == <clientName>).FirstOrDefault();
you can explore your list as below
foreach (ClientEntry client in clientList)
{
//client.ClientName
//client.ClientEmail
}
to find a particular record you can search it as
clientList.Where(p=> p.ClientEmail == "email#domain.com").FirstOrDefault();
To access a specific of item in the list, you input the index / using foreach
string name = clientList[index].ClientName;
foreach(var client in clientList)
{
name = client.ClientName; // access the item one by one
}
To check the existence of certain value of a property, use linq
bool isExist = clientList.Any(i => i.ClientName == "John");
Use Extension Methods !
Something like this, you can write unit test against the extension class easily and also it's straightforward to read.
public static class ClientEntriesExtension
{
public static bool ExistEmail(this IEnumerable<ClientEntry> entries, string targetEmail)
{
return entries.Any(x=>x.ClientEmail == targetEmail);
}
}
bool exist = clientList.ExistEmail(targetEmail)
This is something that worked up to now and now it just, stopped working (I know, weird, there's probably some silly mistake..)
I have a TripsVM, which contains a list of trips. I load these in my service, returning a List<>.
The problem occurs when I iterate over the trips collection and try to get trip.TripCategory.Name, as the TripCategory is empty, even though TripCategoryID has a value.
This all happens at the backend, I load the trips and then try to iterate over them, they are not being send from the page.
I could probably just load the trip by trip itself, but it used to work and this bug just came up after months of usage.
Any suggestions of where to look for bugs would be really appreciated.
Thanks
Error:
Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.
Where error occurs:
foreach (Trip trip in tripsVM.TripsList) {
var a = trip.TripCategory.Name;
TripsVM:
private List<Trip> _TripsList;
public List<Trip> TripsList
{
get
{
if (_TripsList == null)
{
_TripsList = TripsService.GetTrips();
if (_TripsList == null)
_TripsList = new List<Trip>();
}
return _TripsList;
}
set { _TripsList = value; }
}
Service:
public static List<Trip> GetTrips()
{
return DB.Trips.Where(...).OrderBy(...).ToList();
}
Trip class:
public partial class Trip
{
public int TripID { get; set; }
public int TripCategoryID { get; set; }
....
public virtual TripCategory TripCategory { get; set; }
}
Its looks like your DB context disposed before foreach code or LazyLoadingEnabled set to false in context.
In Service add using
using System.Data.Entity;
And modify loading method
public static List<Trip> GetTrips()
{ return DB.Trips.Where(...).Include(t=>t.TripCategory).OrderBy(...).ToList(); }
I think your code looks fine but you should add some if statements to avoid null exception, because you are returning something with where clause, so you might end up with empty query result and empty list, and in that list you are trying to reach an element of a list object:
if(tripsVM.TripsList != null){
foreach (Trip trip in tripsVM.TripsList) {
var a = trip.TripCategory.Name;
}
}
else
{
// handle empty list
}
private List<Trip> _TripsList;
public List<Trip> TripsList
{
get
{
_TripsList = new List<Trip>();
if(TripsService.GetTrips() != null)
{
_TripsList.add(TripsService.GetTrips());
}
return _TripsList;
}
set { _TripsList = value; }
}
First, I'm going to apologize if this is a stupid question. I've been using C# for 16 hours after having not programmed anything since VB6. I'm just trying to hack together a small program for personal use that reads from an old access database and spits out a formatted report in Excel. I apologize for the messy/inefficient code.
Overview: I have two class types, "Zone" and "Device". Each "Zone" has a List of Devices in it. The main program has a List of Zones. Each database has a varying number of "zones" in it, and each "zone" has a varying number of devices assigned to it. I need to parse, sequentially, the zone list and the devices on each zone. I started with structs and arrays and popular opinion seems to be that those are both bad ways to do it, and I wasn't having much luck anyway, so I moved to lists and classes, and it was going well.
I can pull all the "zones" from the database, add them to the list, assign them their labels and IDs. The problem is when I go to read the "devices" from the database, I can't add them to the list within the Zone.
This is the error I get: "Object reference not set to an instance of an object." Which I gather means the object is null?
Here's the relevant code:
Device Class:
public class Device
{
public string Label;
public string Address;
public string Type;
public Device(string Label, string Address, string Type)
{
this.Address = Address;
this.Label = Label;
this.Type = Type;
}
}
Zone Class:
public class Zone
{
public string Label;
public short ID;
public List<Device> Devices;
public Zone(string Label, short ID) {
this.Label = Label;
this.ID = ID;
// ADDED AS PER SUGGESTIONS BELOW
this.Devices = new List<Device>();
}
// Added this to see if it would work, it would not.
public void AddDevice(string Label, string Address, string Type) {
Devices.Add(new Device(Label, Address, Type));
}
}
Initializing and populating Zone List (on button click) (completes successfully)
List<Classes.Zone> Zones = new List<Classes.Zone>();
dbZoneReader = myZoneSelect.ExecuteReader();
while (dbZoneReader.Read())
{
Classes.dbItem dbRow = new Classes.dbItem();
dbRow.Address = Convert.ToInt16(dbZoneReader["DeviceAddress"].ToString());
dbRow.DeviceType = Convert.ToInt16(dbZoneReader["DeviceType"].ToString());
dbRow.Label = dbZoneReader["DeviceLabel"].ToString();
if (dbRow.Label != "" && dbRow.Address > 0)
{
Zones.Add(new Classes.Zone(dbRow.Label,dbRow.Address));
}
}
Adding Devices to their respective Zones:
while (dbReader.Read()) {
Classes.dbItem dbRow = new Classes.dbItem();
string tempZones;
// Acquire/convert device information
dbRow.Node = Convert.ToInt16(dbReader["NodeAddress"].ToString());
dbRow.Loop = Convert.ToInt16(dbReader["LoopSelection"].ToString());
dbRow.Address = Convert.ToInt16(dbReader["DeviceAddress"].ToString());
dbRow.TypeID = Convert.ToInt16(dbReader["TypeID"].ToString());
dbRow.FlashScanID = Convert.ToInt16(dbReader["FlashScanID"].ToString());
dbRow.DeviceType = Convert.ToInt16(dbReader["DeviceType"].ToString());
dbRow.Label = dbReader["DeviceLabel"].ToString();
// Find "proper" zone ID (some zones have multiple IDs, only one is relevant)
tempZones = dbReader["DevicePointMappingList"].ToString();
tempZones = tempZones.Replace("Z", "");
var elements = tempZones.Split(new[] { ',' }, System.StringSplitOptions.RemoveEmptyEntries);
if (elements.Length >= 2) {
ZoneCheck z = new ZoneCheck();
foreach (string items in elements) { if (z.Check(items)) { dbRow.Zone = Convert.ToInt16(items); } }
} else {
if (elements.Length == 1) { dbRow.Zone = Convert.ToInt16(elements[0]); }
else { dbRow.Zone = 0; }
}
// Only add devices that aren't assigned to zone 0, which is non-existent
if (dbRow.Zone > 0) {
// Add new device to zone's device list [THIS IS WHERE IT FAILS]
Zones.Find(z => z.ID == dbRow.Zone).Devices.Add(new Classes.Device("Test", "test", "Test"));
}
}
I've gone through and found out exactly where it fails, and it's the last line where it tries to add the device. Searching here and on google has lead me to believe that I need to initialize the object list... which I believe I've done? I've tried initializing it within the Zone class constructor, and when the Zone is added (which is what it's set too now).
I've confirmed that the Zone object exists, and that the Detectors list within that Zone object isn't null. Kinda stumped, figure I'm doing something that I shouldn't be doing and just don't know better, or I'm missing something really obvious.
The problem is in your Zone class. You need to initialize the List<Device> as follows.
public class Zone
{
public string Label;
public short ID;
public List<Device> Devices;
public Zone(string Label, short ID) {
this.Label = Label;
this.ID = ID;
this.Devices = new List<Device>();
}
// Added this to see if it would work, it would not.
public void AddDevice(string Label, string Address, string Type) {
Devices.Add(new Device(Label, Address, Type));
}
}
The reason is that when you write public List<Device> Devices;, you're not actually creating an object. You're creating a variable that can hold an instance of the specified object. It's only when you pair the variable declaration up with object initialization ( = new List<Device>();) that you get a usable instance of the object.
Thinking of the same issue in terms of a simpler object may help:
public class Foo
{
public string bar; // bar isn't an actual instance of an object, it's just a spot that can hold a string
public void ManipulateBarWithRuntimeError()
{
bar.Substring(0, 1); // "bar" isn't actually set to anything, so how can we take a substring of it? This is going to fail at runtime.
}
public void ManipulateBarWithoutRuntimeError()
{
bar = "Hello, world!";
bar.Substring(0, 1); // bar is actually set to a string object containing some text, so now the Substring method will succeed
}
}
I think the problem is in your Zone class.
Here is my version of your Zone class:
public class Zone
{
public string Label;
public short ID;
public List<Device> Devices;
public Zone(string Label, short ID) {
this.Label = Label;
this.ID = ID;
this.Devices = new List<Device>();
}
// Added this to see if it would work, it would not.
public void AddDevice(string Label, string Address, string Type) {
Devices.Add(new Device(Label, Address, Type));
}
}
This is an only change that I made to your class;
this.Devices = new List<Device>();
Now it might work...
You can also initialize the list inside a getter
public class Zone
{
public string Label;
public short ID;
private List<Device> _devices;
public List<Device> Devices
{
get
{
return this._devices ?? (this._devices = new List<Device>());
}
}
public Zone(string Label, short ID)
{
this.Label = Label;
this.ID = ID;
}
// Added this to see if it would work, it would not.
public void AddDevice(string Label, string Address, string Type)
{
Devices.Add(new Device(Label, Address, Type));
}
}
class IList2
{
static void Main(string[] args)
{
Locations test = new Locations();
Location loc = new Location();
string sSite = "test";
test.Add(sSite);
string site = loc.Site;
Location finding = test.Where(i => i.Site == site).FirstOrDefault();
int index = finding == null ? -1 : test.IndexOf(finding);
}
}
public class Location
{
public Location()
{
}
private string _site = string.Empty;
public string Site
{
get { return _site; }
set { _site = value; }
}
}
public class Locations : IList<Location>
{
List<Location> _locs = new List<Location>();
public Locations() { }
public int IndexOf(Location item)
{
return _locs.IndexOf(item);
}
//then the rest of the interface members implemented here in IList
public void Add(string sSite)
{
Location loc = new Location();
loc.Site = sSite;
_locs.Add(loc);
}
}
IEnumerator<Location> IEnumerable<Location>.GetEnumerator()
{
return _locs.GetEnumerator();
}
I got helped a bit in this post: Trying to call int IList<Location>.IndexOf(Location item) method
I tried to get this working but I always seem to get -1 as the index number. I know string site = loc.Site; is empty after realizing that so I don't know exactly how to get the index from the IList at this point.
To clear up what I'm trying to accomplish, I want to learn how to use the IList interface members and I started out with the IndexOf interface.
The IList is populated with more than just "sSite" but I just reduce the list to just "sSite" for an example purpose.
So in the middle of learning, I hit this bump in the road and been staring at the code for a few days (yes I take breaks and look at other stuff as not to tire myself out).
So the main issue is that I keep getting index = -1.
I'm not clear on what your intention is here but in the code snippet "loc" is never used because you create a new Location in the "Add" method and "site" is (as you've noted) always empty but in the "Add" method you pass in a value and set it on the newly created instance so unless you passed string.Empty as a value the comparison i.Site == site will always be false. If you remove those and rewrite as:
Locations test = new Locations();
string sSite = "test";
test.Add(sSite);
Location finding = test.Where(i => i.Site == sSite).FirstOrDefault();
int index = test.IndexOf(finding);
Then this returns 0 as the index.
Assuming that you have this in the beginning:
Location loc = new Location();
loc.Site = "test";
You will get your index.
Also it is bit confusing, because very unclear what you want to accomplish here.
Note that this line of code:
test.Where(i => i.Site == site).FirstOrDefault();
will return you value only if following is true: "i.Site == site", of course which cannot happen if you provide something not existing in list.