I have a question regarding Lists in c# I have a method:
public void example(Employee emp)
Now I need to write
example();
in another method
But when I do it it shows me an error because I need to put something in () but I don't know what or how.
Thanks!
public void SaveToFile(Employee emp)
{
var path2 = Path.Combine(Directory.GetCurrentDirectory(), "text.txt");
File.AppendAllText(path2, emp2 + Environment.NewLine);
}
//ABOVE ME IS THE METHOD I WANNA CALL
//BELOW IS THE START PROGRAM THING (employeedata is another script)
private static void MainMenu(ref EmployeeData employeeData)
{
employeeData.SaveToFile(Employee emp);
}
After all the comments, I guess this is what you need: You must pass one employee object in parameters when calling your void.
Employeee emp = new Employee();
emp.propertyOne = "stuff";
emp.propertyTwo = "more stuff";
example(emp);
You need to pass in a value between the () which are called parameters, because in your method you are asking for an object with the type of Employee. Please check the following url where you can learn more about parameters:
Parameters in C#
What you are missing is a way to convert your Employee object into a string for writing into a file. Use the .ToString() override to do so.
public class Employee
{
public Employee()
{
// Constructor defaults
ID = 0;
Name = string.Empty;
}
public bool IsValid
{
get
{
// Check if ID and Name are set
return ID > 0 && !string.IsNullOrWhiteSpace(Name);
}
}
public int ID { get; set; }
public string Name { get; set; }
public override string ToString()
{
// String representation of an Employee
return $"{ID}, {Name}";
}
}
Then you can have code that reads and writes to files
public static class EmployeeData
{
public static void AppendToFile(string filename, Employee employee)
{
// Use `ToString()` to convert `Employee` to `string`
File.AppendAllText(filename, employee.ToString() + Environment.NewLine);
}
public static Employee Parse(string description)
{
// Take a string of the form "100, John" and split it
// into parts at the comma
string[] parts = description.Trim().Split(',');
Employee emp = new Employee();
if (parts.Length > 0 && int.TryParse(parts[0].Trim(), out int id))
{
// If first part is an integer, assign it to the ID
emp.ID = id;
}
if (parts.Length > 1)
{
// Assign second part to name
emp.Name = parts[1];
}
return emp;
}
public static List<Employee> ReadFromFile(string filename)
{
// Read all text from file as separate lines
List<Employee> list = new List<Employee>();
string[] lines = File.ReadAllLines(filename, Encoding.UTF8);
foreach (var line in lines)
{
// Convert each line of text into an Employee object
Employee emp = Parse(line);
if (emp.IsValid)
{
// If the object is valid add to the list
list.Add(emp);
}
}
return list;
}
}
and the above is used in the following proof of concept code below:
internal class Program
{
static void Main(string[] args)
{
Employee emp1 = new Employee()
{
ID = 1,
Name = "Peter",
};
EmployeeData.AppendToFile("test.txt", emp1);
Employee emp2 = new Employee()
{
ID = 2,
Name = "Maria",
};
EmployeeData.AppendToFile("test.txt", emp2);
List<Employee> employees = EmployeeData.ReadFromFile("test.txt");
foreach (var item in employees)
{
Console.WriteLine(item);
// This calls item.ToString()
}
}
}
which prints the following on the console window the first time its run
1, Peter
2, Maria
Note that each time the program runs it adds to the above creating duplicates. That is a subject of a different question, on how to write an .Equals() function to check for duplicates.
Related
I use FastMember to get values out of objects and nested objects. If a property is a string or int everything works fine. But now I want to get the values also for collections. Here is my code so far:
// Set accessor
var sourceAccessor = ObjectAccessor.Create(source);
if (sourceAccessor.Target.GetType().GetInterface(nameof(ICollection)) != null || sourceAccessor.Target.GetType().GetInterface(nameof(IEnumerable)) != null)
{
foreach (/* idk */)
{
// READ & RETURN VALUES HERE
}
}
An object could look like this:
{
Id: 1,
Surname: Doe,
Prename: John,
Professions: [
{ Name: ab },
{ Name: xy }
]
}
Which means professions would result in a problem.
Any advise how I can solve this problem? Thanks!
It's not obvious from the question what the data type of the source variable is, but you should just be able to check if the value returned by the accessor implements IEnumerable or not and act accordingly.
Here's a quick worked example that iterates over the Professions property of a 'Person' object and just dumps the ToString() representation to the console - if you wanted to dive into each Profession object using FastMember you could construct another ObjectAccessor to do it, I guess - it's not clear what your goal is once you're iterating.
The same tactic will work if you're building the ObjectAccessor directly from an array - you just check if the accessor.Target is IEnumerable and cast-and-iterate in a similar fashion.
class Program
{
static void Main(string[] args)
{
var p = new Person
{
Professions = new List<Profession>
{
new Profession("Joker"),
new Profession("Smoker"),
new Profession("Midnight toker")
}
};
var accessor = ObjectAccessor.Create(p);
var professions = accessor[nameof(Person.Professions)];
if (professions is IEnumerable)
{
foreach (var profession in (IEnumerable)professions)
{
Console.WriteLine(profession);
}
}
}
}
class Person
{
public List<Profession> Professions { get; set; }
}
class Profession
{
public string Name { get; set; }
public Profession( string name)
{
Name = name;
}
public override string ToString()
{
return Name;
}
}
A quick question on OOP. I am using a list together with a class and class constructor. So I use the class constructor to define the data set and then add each record to my list as the user creates them.
My questions is once the data is in the list and say I want to alter something is it good practice to find the record, create an instance using that record and then use my class methods to do whatever needs doing - and then put it back in the list?
For example below I have my class with constructor. Lets say I only want the system to release strCode if the Privacy field is set to public. Now just using Instances I would use for example Console.WriteLine(whateverproduct.ProductCode) but if the record is already in a list do i take it out of the list - create an instance and then use this method?
class Product
{
private String strCode;
private Double dblCost;
private Double dblNet;
private String strPrivacy;
public Product(String _strCode, Double _dblCost, Double _dblNet, String _strPrivacy)
{
strCode = _strCode;
dblCost = _dblCost;
dblNet = _dblNet;
strPrivacy = _strPrivacy;
}
public string ProductCode
{
get
{
if (strPrivacy == "Public")
{
return strCode;
}
else
{
return "Product Private Can't release code";
}
}
}
Lets say we have the following:
public class Test
{
public int Id { get; set; }
public string Name { get; set; }
public decimal Amount { get; set; }
private string _test = "Some constant value at this point";
public string GetTest()
{
return _test;
}
public void SetTest()
{
//Nothing happens, you aren't allow to alter it.
//_test = "some constant 2";
}
}
public class Program
{
public static void Main(string[] args)
{
List<Test> listOfTest = new List<Test>()
{
new Test() {Id = 0, Name = "NumberOne", Amount = 1.0M},
new Test() {Id = 1, Name = "NumberTwo", Amount = 2.0M}
};
Test target = listOfTest.First(x => x.Id == 0);
Console.WriteLine(target.Name);
target.Name = "NumberOneUpdated";
Console.WriteLine(listOfTest.First(x => x.Id == 0).Name);
Console.WriteLine(listOfTest.First(x => x.Id == 0).GetTest());//This will alsways be "Some constant value at this point";
Console.ReadLine();
}
}
Technically you could do away with the SetTest method entirely. However, I included it to demonstrate, what it would look like, if you wanted to alter _test.
You don't want to ever create a new instance of a class, you already have an instance of. you can just alter the class where it is allowed by the author of the class, where you need to. And keep that class reference for as long as you need it. Once you are done, the reference will be garbage collected, once the program finds no active reference to your object(instance).
I am trying to output from Array list to a Listbox. My problem is I think is I do not know how to connect the Class to the Generic array list a made? The end result should look like this:
And the information should be then sorted like so: all the information enters the first list box, and then the above 18 goes to adults, and the below 18 to kids. My class looks like this:
namespace Patients
{
public class Person
{
public string Name { get; set; }
public int Age { get; set; }
public String Password { get; set; }
public Person() //Constructor
{
Age = 0;
Password = "";
}
public Person (string name, int age, string password) //Parameters
{
this.Name = name;
this.Age = age;
this.Password = password;
}
public override string ToString() //
{
return Name + Age.ToString() + Password; //outputs as a string
// return Name + " (" + Age + " years) " + Password ;
}
}
}
namespace Patients
{
public partial class WebForm1 : System.Web.UI.Page
{
public static void Page_Load(object sender, EventArgs e)
{
}
public void ButtonAdd_Click(object sender, EventArgs e)
{
Person p = new Person();
List<string> People = new List<string>();
People.Add(TextBoxName.Text);
People.Add(TextBoxAge.Text);
People.Add(TextBoxPassword.Text);
foreach (object Person in People)
{
ListBoxAll.Items.Add(p.Name + p.Age.ToString() + p.Password);
}
if (p.Age > 18)
{
ListBoxAdults.Items.Add(p.Name + p.Age.ToString() + p.Password);
}
else
{
ListBoxKids.Items.Add(p.Name + p.Age.ToString() + p.Password);
}
}
}
}
I think your problem is, that you don't set the Properties. In Fact you don't need a List at all, but you can use a List to keep hold of your patients. It's still not necessary though:
namespace Patients
{
public partial class WebForm1 : System.Web.UI.Page
{
// Define Property and initialize List
public List<Person> patients{ get; } = new List<Person>();
public static void Page_Load(object sender, EventArgs e)
{
}
public void ButtonAdd_Click(object sender, EventArgs e)
{
// Use the Constructor with Parameters
Person p = new Person(TextBoxName.Text, TextBoxAge.Text, TextBoxPassword.Text);
// Add your patient to your List
patients.Add(p);
// Use the ToString() of your Person
ListBoxAll.Items.Add(p.ToString());
if (p.Age > 18)
{
ListBoxAdults.Items.Add(p.ToString());
}
else
{
ListBoxKids.Items.Add(p.ToString());
}
}
}
}
Looks like you are mixing and matching a bit.
Try something like this.
Person p = new Person();
p.Name = TextBoxName.Text;
p.Age= TextBoxAge.Text;
p.Password= TextBoxPassword.Text;
ListBoxAll.Items.Add(p);
A few tricks that are nice to us, first off you can declare defaults for properties like so:
public string Name { get; set; } = "Steve";
public int Age { get; set; } = 1;
public String Password { get; set; } = "password";
However, it should also be noted that "" is the default for strings already and 0 is the default for non-nullable int, so you don't even need to worrying about those default values.
Declaring Age = 0; in the constructor is basically a waste of time in this case. (If it was a nullable int however the default is null)
Next up, since you are okay with defaults, you don't need to declare properties in the constructor like you are.
You can completely remove the constructor and just do the following:
var myPerson = new Person { Name = "Steve", Age = 18, Password = "Foo" };
Next up, you are losing all your existing people as soon as you exit the scope of the button click.
Instead you'll want to declare two lists of people outside the scope of the click method (that way they persist), something like "Adults" and "Children"
Then perhaps make a method called "PopulateLists" that would do the following:
Clear all list boxes
Add to each box the list of each groups names that apply (you can make an IQueryable by using Linq and Select statements on your list)
When you click the button, you should make a new person, assign it to the right list, then call PopulateLists()
Here's the info you need to get started:
Linq selection to get list of properties (in this case Im going to turn a List of People into a List of Ages, you can do the same with names though)
var ages = People.Select(p => p.Age);
The .Items property of a ListBox works the same as a list, it just visually shows itself. It's a list of strings specifically.
So for example you can do things like...
MyListBox.Items.Clear();
MyListBox.Items.Add(...);
MyListBox.Items.AddRange(...);
etc etc.
That should get you started!
As you see in the title above, i need to run a FOR loop to create 4 plumbers from the default constructor. After they are created (within the FOR loop), change their names, add them to the employee list and display in listbox. So basically, plumbers is actually a list declared in another class called EmployeeList. Wehn i tried changing their names to random ones, i get like an error msg saying 'Index is out of range'. Can someone help me with this?
Form Code
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
//create class-level employee list
EmployeeList plumbers = new EmployeeList();
private void Form1_Load(object sender, EventArgs e)
{
//run a for loop to create 4 plumbers from the default constructor.
for (int i = 0; i < plumbers.Count; i++)
plumbers[i] = new Employee();
//After they are created (within the FOR loop), change their names,
//plumbers[0].Name = "Nicole Fernandez";
//add them to the employee list
//display in listbox
foreach (Employee item in plumbers.Employees)
{
lstDisplay.Items.Add(item.DisplayData());
}
}
Employee List Class Code
class EmployeeList
{
//use private access modifier to create a list of employee
private List<Employee> employees = new List<Employee>();
public List<Employee> Employees
{
get { return employees; }
set { employees = value; }
}
//return the count of the employee list, use lambda operator
public int Count => employees.Count();
//create default constructor
public EmployeeList() { }
//create a method that adds employee sent to the list. No return value
public void AddEmp(Employee emp)
{
employees.Add(emp);//add employee to the list
}
//create employee from data sent. No return value
public void AddEmp(string inName, int inID, decimal inHourlyWage)
{
//declare a variable
Employee emp = new Employee(inName, inID, inHourlyWage);
//call the other AddEmp
AddEmp(emp);
}
//create a method that deletes employee from the list. No return value
public void DeleteEmp(Employee emp) => employees.Remove(emp);
//insert employee at the index
public void InsertEmp(Employee emp, int index) => employees.Insert(index, emp);
//create an indexer
public Employee this[int i]
{ //q12 - indexer property with exception
get
{
if (i < 0 || i >= Count)
throw new ArgumentOutOfRangeException(i.ToString());
return employees[i];
}
set { employees[i] = value; }
}
}
Employee Class Code
class Employee
{
//use auto-implemented property
public int ID { get; set; }
public string Name { get; set; }
public decimal HourlyWage { get; set; }
public decimal TotalPay { get; set; }
//create static integer that starts at 1
private static int NextID = 1;
//create a default constructor with default values
public Employee()
{
ID = NextID++;
Name = "John Doe";
HourlyWage = 15.25m;
TotalPay = 0.0m;
}
//create the custom constructor sending in 3 parameters
public Employee(string inName, int inID, decimal inHourlyWage)
{
Name = inName;//set name, no validation is required
//validate ID is between 1 and 250. if not, set to nextID available
if (inID <= 1 && inID >= 250)
NextID = inID;
//validate hourly wage is between 12.50 and 20. If not, set to 15.25
if (inHourlyWage <= 12.50m && inHourlyWage >= 20.0m)
inHourlyWage = 15.25m;
TotalPay = 0;//set total pay to 0
}
public string DisplayData() => ID + "\t" + Name + "\t" + HourlyWage.ToString("c") + "\t" + TotalPay.ToString("c");
}
First, if you want to create a list of 4 plumbers using a loop, then you need the loop to iterate 4 times. This is normally done by setting the initial counter value to 0, then looping while it is less than the number you want:
for (int i = 0; i < 4; i++)
Also, your plumbers object is of type EmployeeList, but you're trying to access it with an indexer as if it's a List or an Array. Instead, you should use the method you created to add new employees:
// Run a for loop to create 4 plumbers from the default constructor.
for (int i = 0; i < 4; i++)
{
plumbers.AddEmp(new Employee());
}
Since there doesn't appear to be any public method to update an existing plumber, we can just access the Employees list directly to rename the plumbers. There are a couple of ways to do it. One would be to use a loop and use part of the loop counter in the name:
// After they are created (within the FOR loop), change their names
for(int i = 0; i < plumbers.Employees.Count; i++)
{
plumbers.Employees[i].Name = string.Format("Plumber #{0}", i);
}
Another way is to do it by hand, giving each plumber a normal name:
plumbers.Employees[0].Name = "Nicole";
plumbers.Employees[1].Name = "Rufus";
plumbers.Employees[2].Name = "Mark";
plumbers.Employees[3].Name = "John";
Or, if you want to be really fancy, you can generate a list of names (I pulled these from the top baby names of 2016), then for each plumber grab a random name from the list and assign it (and remove it from the list so the plumbers all have unique names):
//After they are created (within the FOR loop), change their names
// Generate a list names
var nameCandidates = new List<string>
{
"Olivia", "Amelia", "Charlotte", "Ava", "Isla", "Arabella", "Aurora",
"Adeline", "Penelope", "Eleanor", "Ezra", "Asher", "Atticus",
"Declan", "Oliver", "Silas", "Milo", "Levi", "Henry", "Wyatt"
};
// Loop through each plumber and choose a random name
var rnd = new Random();
foreach(var plumber in plumbers.Employees)
{
// Choose a random name, assign it, and remove it from candidates
var nameIndex = rnd.Next(nameCandidates.Count);
plumber.Name = nameCandidates[nameIndex];
nameCandidates.RemoveAt(nameIndex);
}
I have two classes, Customer and Country. Customer has a property called HomeCountry, which i have decorated with a custom attribute called "Lookup" and takes a string parameter "Country". The purpose is, when I am using the Customer class, the item in HomeCountry must exist in the Country class (which happens to be a list).
I am using reflection to iterate the Customer class, it finds the attribute and i want it to check the value in the list of country items. So far I have:
foreach (PropertyInfo _pi in object.GetType().GetProperties()) {
IEnumerable<Attribute> _attrs = _pi.GetCustomAttributes();
foreach (Attribute _a in _attrs) {
Object obj = Activator.CreateInstance(_type, null);
// what goes here?
}
}
I have a method:
public T Populate<T>(params string[] _parameters)
I think i want to do
List<obj> v = populate<obj>();
or
List<typeof(obj)> v = populate<typeof(obj)>();
but obviously nothing works! Can anybody help me ?
Thanks
OK i will try and provide a full example:
I have a CUSTOMER_ORDER class:
public class CUSTOMER_ORDER {
public CUSTOMER_ORDER() {}
[Key(0)]
public string OrderNumber {get;set;}
public MPCCOM_SHIP_VIA ShipVia {get;set;}
}
Then the MPCCOM_SHIP_VIA class:
public class MPCCOM_SHIP_VIA {
public MPCCOM_SHIP_VIA() {}
[Key(0)]
public string ID {get;set;}
public string Description {get;set;}
}
I have a method called Populate< T > which takes a class and then uses reflection to loop all the properties and build a select statement, executes it, and then returns the data and populates the object:
public T Populate<T>(params string[] #Parameters)
{
Type _t = typeof(T);
dynamic _o = Activator.CreateInstance(typeof(T), null);
SqlBuilder _sb = new SqlBuilder();
_sb.Table = string.Format("{0}.{1}", _Owner, _t.Name.ToString());
foreach (PropertyInfo p in _t.GetProperties(Utilities.BindingFlags))
{
if (p.GetMethod.IsPrivate == false) _sb.Fields.Add(p.Name.ToString());
IEnumerable<Attribute> _attrs = p.GetCustomAttributes();
foreach (Attribute _a in _attrs)
{
if (_a.TypeId.ToString().Equals(typeof(Key).FullName))
{
int _position = ((Key)_a).Position;
try
{
string _parameter = #Parameters[_position];
_sb.Where.Add(string.Format("{0} = '{1}'", p.Name, _parameter));
}
catch {}
}
}
}
using (OleDbCommand _cmd = new OleDbCommand())
{
_cmd.Connection = this._cn;
_cmd.CommandText = _sb.SQL;
if (_trn != null) _cmd.Transaction = _trn;
_cmd.CommandType = System.Data.CommandType.Text;
using (OleDbDataReader _reader = _cmd.ExecuteReader())
{
if (_reader.Read())
{
for (int x = 0; x < _reader.FieldCount; x++)
{
foreach (PropertyInfo p in _t.GetProperties(Utilities.BindingFlags))
{
if (p.GetMethod.IsPrivate == false)
{
if (p.Name.Equals(_reader.GetName(x).ToString()))
{
dynamic _val = _reader.GetValue(x);
if (p.ReflectedType.BaseType.Name.Equals(""))
{
// what goes here!
}
try
{
p.GetSetMethod(true).Invoke(_o, new object[] { _val });
}
catch { }
break;
}
}
}
}
}
else
{
throw new DatabaseObjectNotFound(_t.Name.ToString(), string.Join(",",#Parameters));
}
}
}
return (T)_o;
}
So, as i read an order, the source DB gets the key to the MPCCOM_SHIP_VIA in the respective field, i want to call the same Populate method against the MPCCOM_SHIP_VIA object with the key. I hope this makes more sense demonstrating what i want to do. And thanks
After some hunting around, this is the answer i was looking for...
MethodInfo method = typeof(class).GetMethod("Populate");
method = method.MakeGenericMethod(p.PropertyType);
_val = method.Invoke(class, new object[] { _prms });
I guess my issue was i was asking the wrong question!