New here, I've been learning c# for about a month.
Anyway, I've been searching StackOverflow for a couple of days now and couldn't find a specific answer to my problem...
//Here's my Class
public class Guy
{
public static int ID { get; set; }
public static int LifeExpectancy { get; set; }
public static bool Living { get; set; }
public Guy(int id, int lifeExpectancy, bool living)
{
ID = id;
LifeExpectancy = lifeExpectancy;
Living = living;
}
}
What I'm trying to do is create a specific number of "someGuy" objects to then put them into a public list using this method...
public static List<Guy> Guys = new List<Guy>();
public static void makeSomeGuys(int howManyGuys)
{
for (int i = 0, i <= howManyGuys; i++)
{
int id = i;
int lifeExpectancy = 80;
bool alive = true;
Guys.Add(New Guy(id, lifeExpectancy, alive));
Console.WriteLine("Made a new Guy {0}", id);
}
return;
}
Questions in order of importance:
How do I access a specific object as well as its parameters? (Accessing from the list "Guys".)
How do I access an object from this list in another class? (Not that I absolutely need to, I'm curious)
Can I search for an object in a list by using its parameters? (As opposed to doing something like... humanPopulation[number])
Should I create a new list for objects that have had their parameters modified? (As opposed to leaving it in the original list)
Is it possible to remove items from a list? (Just in general, is that a thing people do? if so, why?)
I really only need the first question answered. The rest of them are just a bonus. Thanks!
First you need to remove the static modifier from the properties of the Guy class, i.e.:
public int ID { get; set; }
public int LifeExpectancy { get; set; }
public bool Living { get; set; }
because static causes the property to be an attribute of the class itself, rather than the instances of the class (the individual 'guys').
To access life expectancy of the first guy (the zeroth):
Console.WriteLine(Guys[0].LifeExpectancy);
To access life expectancy of the fifth guy:
Console.WriteLine(Guys[4].LifeExpectancy);
using System;
using System.Collections.Generic;
using System.Linq;
namespace test
{
public class Guy
{
private int m_ID;
private int m_LifeExpectancy;
private bool m_Living;
public int ID
{
get { return m_ID; }
set { m_ID = value; }
}
public int LifeExpectancy
{
get { return m_LifeExpectancy; }
set { m_LifeExpectancy = value; }
}
public bool Living
{
get { return m_Living; }
set { m_Living = value; }
}
public Guy(int id, int lifeExpectancy, bool living)
{
ID = id;
LifeExpectancy = lifeExpectancy;
Living = living;
}
}
public class MyFactory
{
public IList<Guy> MakeSomeGuys(int howManyGuys)
{
IList<Guy> localGuys = new List<Guy>();
for (int i = 0; i <= howManyGuys; i++)
{
int id = i;
int lifeExpectancy = 80;
bool alive = true;
localGuys.Add(new Guy(id, lifeExpectancy, alive));
Console.WriteLine("Made a new Guy {0}", id);
}
return localGuys;
}
}
public class program
{
public void Main()
{
MyFactory mf = new MyFactory();
IList<Guy> guys = mf.MakeSomeGuys(5);
//How do I access a specific object as well as its parameters? (Accessing from the list "Guys".)
int GetFirstGuyId = guys.FirstOrDefault().ID; //LEARN LINQ
//How do I access an object from this list in another class? (Not that I absolutely need to, I'm curious)
//you need to learn about object oriented encapsulation for better understanding.
//Can I search for an object in a list by using its parameters? (As opposed to doing something like...humanPopulation[number])
Guy guyById = guys.Where(g => g.ID == 5).FirstOrDefault(); // returns the first match (need to learn lambda expression)
//Should I create a new list for objects that have had their parameters modified? (As opposed to leaving it in the original list)
// you need to learn about passing values by value / reference (by reference you already changing the original!).
//Is it possible to remove items from a list? (Just in general, is that a thing people do? if so, why?)
//yes
guys.Remove(guyById);
}
}
}
You're likely new to C# and OO programming, so I've included some good links in this answer.
Regarding question 1 only:
Firstly, your Guy class properties aren't properly encapsulated. Make sure you properly scope the ID, LifeExpectancy and Living properties like shown in this article.
If you'd like to access a specific item, that is, a Guy with a particular ID, you'd be better off using an associative container like Dictionary.
If you're happy with the List container, you need to use the Find method on Guys as shown in the example at the link. You'll notice the term Predicate in the documentation, this link will elaborate.
Related
I've made a code that has an interface and an abstract class to make my main function to work with both objects. As I started to work around my function everything was working perfectly until I needed to get a function from the object itself.
My function is:
void addNode<T>(List<T> genericList) where T : IGraphs{
T genericNode = (T)Activator.CreateInstance(typeof(T));
genericNode.Number = contDirected;
if (genericList.Count > 0)
{
string connectedNode = "";
while (!connectedNode.Equals("0") && genericList.RemainingNodesExist(undirectedGraphs, genericNode))
{
}
}
}
}
Obviously the function is not yet finished but the problem is on my last "while". As I try to get the method "RemainingNodesExist", the IDE gives me an advice saying that List does not have a definition for the method. Im not sure why is that since I have it on my classes:
public interface IGraphs
{
public int Number { get; set; }
public List<int> LinkedNumbers { get; set; }
}
public abstract class AbstractGraphs<T>
{
public abstract bool RemainingNodesExist(List<T> list, T node);
}
And on the classes that inherit from those above:
public class DirectedGraph: AbstractGraphs<DirectedGraph>, IGraphs
{
public int Number { get; set; }
public List<int> LinkedNumbers { get; set; }
public DirectedGraph()
{
Number = Number;
LinkedNumbers = new List<int>();
}
public override bool RemainingNodesExist(List<DirectedGraph> list, DirectedGraph node)
{
int numbersConnected = node.LinkedNumbers.Count;
if (numbersConnected != list.Count)
{
return true;
}
return false;
}
public UndirectedGraph()
{
Number = Number;
LinkedNumbers = new List<int>();
}
public int Number { get; set; }
public List<int> LinkedNumbers { get; set; }
public override bool RemainingNodesExist(List<UndirectedGraph> list, UndirectedGraph node)
{
int numbersConnected = node.LinkedNumbers.Count;
if (numbersConnected != list.Count)
{
return true;
}
return false;
}
To better summarize whats my goal...
I have 2 objects that are exactly the same in properties, but the methods will probably be different in some situations. I used the generic class T because the program will use a list of objects not yet defined that can be any of the two objects mentioned above. What I want my program to do is run the "addNode" function and run the method of both objects based on their type.
Has anyone had to deal with a similar problem or could give me some direction on how to solve this?
I am very suspicious of this code base, it looks way way too complicated.
But to answer your specific question
while (!connectedNode.Equals("0") && genericList.RemainingNodesExist(undirectedGraphs, genericNode))
attempts to call a method on genericList, thats a List<XXX> passed as a parameter
That method (RemainingNodesExist) is defined here
public abstract class AbstractGraphs<T>
{
public abstract bool RemainingNodesExist(List<T> list, T node);
}
Its a method of a class called AbstractGraphs<T>
Which has no relation to List<AnythinG>
Its hard to say what you need to change because this is such a convoluted set of classes.
Maybe if you can explain why you think that method would be callable on a list that might make it clearer
I have an application where i have say 10 objects of different types. I wish to have them in same list and iterate through them on many occasions. I cant push them into one list because they are of different types. So i created an interface and created a property that all objects share. Now i have the list of objects and type of the list is the "interface". When i iterate through the object, i can't access the specific properties of the object because the compiler will only know at runtime what object it is. So if i try to code Object_A.Name, visual studio will show error because it doesn't know they type of object. I can obviously do an if else or something similar to find the type of object and cast it, but i want to know of there is a better way, or if this whole approach of having an interface is wrong and if i should have begun in a different direction.
In the code below, i want to get the Devname, which i can't because its not part of the interface, but belongs to every object. I could make it part of the interface, but every now and then i may need to get a specific property. hence wanting to know if there is a way to do it.
foreach (ICommonDeviceInterface device in Form1.deviceList)
{
if (device.DevName.Equals(partnername))
{
return device.Port[portNo].PortRef;
}
}
One way you could do this is by using reflection to try to get the property value of a named property from an object, using a helper method like:
public static object GetPropValue(object src, string propName)
{
return src?.GetType().GetProperty(propName)?.GetValue(src, null);
}
Credit for above code goes to: Get property value from string using reflection in C#
This requires no checking types or casting, it just returns the value of the property, or null if it doesn't contain the property.
In use it might look like:
private static void Main()
{
// Add three different types, which all implement the same interface, to our list
var devices = new List<ICommonDeviceInterface>
{
new DeviceA {DevName = "CompanyA", Id = 1},
new DeviceB {DevName = "CompanyB", Id = 2},
new DeviceC {Id = 3},
};
var partnerName = "CompanyB";
foreach (var device in devices)
{
// Try to get the "DevName" property for this object
var devName = GetPropValue(device, "DevName");
// See if the devName matches the partner name
if (partnerName.Equals(devName))
{
Console.WriteLine($"Found a match with Id: {device.Id}");
}
}
}
Classes used for the sample above:
interface ICommonDeviceInterface
{
int Id { get; set; }
}
class DeviceA : ICommonDeviceInterface
{
public int Id { get; set; }
public string DevName { get; set; }
}
class DeviceB : ICommonDeviceInterface
{
public int Id { get; set; }
public string DevName { get; set; }
}
class DeviceC : ICommonDeviceInterface
{
public int Id { get; set; }
}
Use "as" and "is" to know what type of interface
public class A : ICommonDeviceInterface
{
public int AMember;
}
public class B :ICommonDeviceInterface
{
public int BMember;
}
foreach (ICommonDeviceInterface device in Form1.deviceList)
{
if(device is A)
{
A a = device as A;
a.AMember = 100;
}
else if(device is B)
{
B b = device as B;
b.BMember = 123;
}
}
have tried some searches. Probably my lack of knowledge that I'm not using the right search terms or perhaps just not understanding the answers.
I have a method that is being passed an object, which I want to output a particular value to a text file.
I already know the object will be a List< someClass > of a few different possible classes (customers/employees/items etc). But all of the classes contain the same string property (e.g.) string idNumber.
So something like this:
public static void OutputFile(object myInput)
{
foreach (someGenericObject in (List<anyType>)myInput)
{
string textToOutput = someGenericObject.idNUmber;
//output the text to somewhere else here
}
}
I feel like as long as I know that it will always contain a this "idNumber" property regardless of the type, that I should be able to reference it somehow. But I just can't seem to get my head around it?
The error I typically get is something like:
Cannot cast List< Employee > to List< object > etc.
Thanks in advance
As I suggested in the comments, if you have the ability to modify these classes, you can have them all inherit from an interface IHasIdNumber with an idNumber property.
Your method would then become:
public static void OutputFile(IEnumerable<IHasIdNumber> myInput)
{
foreach (var item in myInput)
{
string textToOutput = item.idNUmber;
//output the text to somewhere else here
}
}
There are a few ways you can solve this.
Recommended way: Implement common interface:
public interface INumberable { // I'm sure you can come up with a better name...
string IDNumber { get; set; }
}
And then all the possible classes that can be passed into the method will implement INumberable. Your method can then look like this:
public static void OutputFile(List<INumerable> myInput)
{
foreach (var someGenericObject in myInput)
{
string textToOutput = someGenericObject.idNUmber;
//output the text to somewhere else here
}
}
Not-so-recommended way: Reflection:
Type t = someGenericObject.GetType();
var p = t.GetProperty("idNumber");
string theStringYouWant = (string)p.GetValue(someGenericObject);
Note that this is not very safe.
You can use [dynamic].
foreach (var someGenericObject in (dynamic)myInput)
{
//...
}
If all your classes have the same property you want to access in foreach loop you can do in via interface.
public interface ISmth {
int MyProperty { get; set; }
}
public class Student : ISmth {
public int MyProperty { get; set; }
}
public class Employee : ISmth {
public int MyProperty { get; set; }
}
public static void DoSmth(object myObj) {
foreach(ISmth item in (List<object>)myObj) {
Console.Write(item.MyProperty);
}
}
List<Student> stdList = new List<Student>();
DoSmth(stdList.Cast<object>().ToList());
Does there exist in any System namespace in C# a container, which can accept only some types?
For example I want to create my list in which I'll have only objects with type Class1 and int:
//accept only type Class1 and int;
MYLIST lst = new MYLIST(typeof(Class1), typeof(int));
lst.Add( 23 ); // OK
lst.Add( new Class1() ); // OK
lst.Add( "text" ); // wrong, not accepted type
Is something like that in .NET or I have to write it on my own? Thanks.
The C# type system does not allow you to express something like "either Class1 or int". Having said that, you can use overloads to get half of the way there:
class MyClass
{
private List<object> _items = new List<object>();
public void Add(int value) { _items.Add(value); }
public void Add(Class1 value) { _items.Add(value); }
...
}
The real tricky question is how you get things out, rather than how you put things in. There are several possibilities: get everything out as object (by implementing IEnumerable<object>), and maybe special methods like GetInt(int index) and GetClass1(int index).
The answer is NO, there is NO such list in C# and for VERY GOOD reason.
You could make a wrapper, but i'd advise against it.
public class CustomListWrapper< T, F>
{
private readonly List<object> internalList;
public CustomListWrapper()
{
this.internalList = new List<object>();
}
public void Add(object item)
{
if(!(item is T || item is F))
throw new Exception();
this.Add(item);
}
}
PS: before the downvote, for how to get the object out...well this is why this is a fairly bad idea, but you'd have to do an "is" on the type you get out to be able to cast it to the proper type.
Again, not exactly sure why you would EVER need to do this.
No. You will have to create your own. You can implement ICollection or IEnumerable or IList or whatever. You have lots of flexibility here. But bottom line, the answer is no, no such collection exists that allows you to limit the types in the collection to certain types automatically.
You cannot achieve this in a direct way. The item type of a List<T> must be a base type common to all the types you want to add to the list.
You could have a List<object> or a wrapper around a List<object> of cause. However, you would have to check at runtime if the items added to it are of the correct types and you would have to cast the items that you retrieve from the list to the correct type.
If you want to store different types in the same list, a good option would be to create an interface that all of these types must implement
public interface ICommonInterface
{
int Number { get; }
string Text { get; }
}
public Class1 : ICommonInterface
{
public int Number { get; set; }
public string Text { get; set; }
public string AnAdditionalProperty { get; set; }
}
public NumberWrapper : ICommonInterface
{
public NumberWrapper (int number)
{
this.Number = number;
this.Text = number.ToString();
}
public int Number { get; private set; }
public string Text { get; private set; }
}
public TextWrapper : ICommonInterface
{
public TextWrapper (string text)
{
this.Text = text;
int i;
Int32.TryParse(text, out i);
this.Number = i;
}
public int Number { get; private set; }
public string Text { get; private set; }
}
Then you can declare your list as
List<ICommonInterface> lst = new List<ICommonInterface>();
lst.Add(new Class1());
lst.Add(new NumberWrapper(77));
lst.Add(new TextWrapper("hello"));
Console.WriteLine(lst[0].Text);
why not just wrap a List<>, and make two add methods, one that accepts int, another that accepts Class1
This is probably a simple question. Suppose I have a object called Users and it contains a lot of protected variables.
Inside that Users class I have a method that creates a temporary Users object, does something with it, and if successful, transfers all the variables from the temp Users object into the one I have.
Is there some fast way to transfer all the variables from one Users object into another Users object without doing this using C#?
this.FirstName = temp.FirstName;
this.LastName = temp.LastName;
........75 variables later......
this.FavoriteColor = temp.FavoriteColor
A better approach is to implement the IClonable interface. But you'll find it doesn't save you a lot of work.
You should check out cloning in C#.
Deep cloning objects
I think serializing and then deserializing an object will create a new object instance. This should be identical to the former object.
A better solution might be to move whatever this method is outside of your class, and then just assign the temp user object to your main user object reference like so:
_User = tmpUser;
sparing you the 75 lines of code. Whenever I have a class creating an instance of itself inside one of its own methods, I always like to blink a couple of times and make sure I really need to be doing that.
There's always the reflection option. Something substantially similar to this:
public static void Copy(object source, object target)
{
foreach (System.Reflection.PropertyInfo pi in source.GetType().GetProperties())
{
System.Reflection.PropertyInfo tpi = target.GetType().GetProperty(pi.Name);
if (tpi != null && tpi.PropertyType.IsAssignableFrom(pi.PropertyType))
{
tpi.SetValue(target, pi.GetValue(source, null), null);
}
}
}
Doesn't require the source and the target to have any relation what-so-ever, just a name and an IsAssignable check. It has the interesting side effects if you're using reference types anywhere, but for the kind of situation you just described, this isn't a bad option to explore.
class sourceTester
{
public bool Hello { get; set; }
public string World { get; set; }
public int Foo { get; set; }
public List<object> Bar { get; set; }
}
class targetTester
{
public int Hello {get; set;}
public string World { get; set; }
public double Foo { get; set; }
public List<object> Bar { get; set; }
}
static void Main(string[] args)
{
sourceTester src = new sourceTester {
Hello = true,
World = "Testing",
Foo = 123,
Bar = new List<object>()
};
targetTester tgt = new targetTester();
Copy(src, tgt);
//Immediate Window shows the following:
//tgt.Hello
//0
//tgt.World
//"Testing"
//tgt.Foo
//0.0
//tgt.Bar
//Count = 0
//src.Bar.GetHashCode()
//59129387
//tgt.Bar.GetHashCode()
//59129387
}