In my Class i need to set one property value according to another:
public class Quantities
{
private int _quant;
public int Quant
{
get { return _quant; }
set
{
if (Unit == "K")
{
_quant = value / 1000;
}
else
{
_quant = value;
}
}
}
public string Unit { get; set; }
}
according to several tests i made it works fine but i still don't know if it's safe to do this.
is it possible that the Quant Property will be evaluated before the Unit Property or does the compiler (or JIT) knows that it should assign the Unit Property first?
This has nothing to do with the compiler or the JIT. Your code assigns the values. You need to know the order in which they should be assigned.
BTW: Your code exhibits temporal coupling. It would be better to make at least the Unit unchangeable by making the property readonly and by providing a constructor that requires the unit:
public class Quantities
{
private readonly string _unit;
private int _quant;
public Quantities(string unit)
{
if(unit == null) throw new ArgumentNullException("unit");
_unit = unit;
}
public int Quant
{
get { return _quant; }
set
{
if (Unit == "K")
{
_quant = value / 1000;
}
else
{
_quant = value;
}
}
}
public string Unit { get { return _unit; } }
}
This class now can't be used in an incorrect way.
For more points that can be improved with your class, please refer to Lasse's answer.
Code on the outside of this class must know about this dependency or you risk someone changing Unit without re-setting Quant:
var x = new Quantities(); // why no constructor for this?
x.Unit = "K";
x.Quant = 1700; // why int? this will now be 1, not 1.7
x.Unit = "M";
Personally I would make the class a struct, and make it immutable:
public struct Quantity
{
private readonly double _Value;
private readonly string _Unit;
public Quantity(double value, string unit)
{
_Value = value;
_Unit = unit;
}
public double Value
{
{
return _Value;
}
}
public double Unit
{
{
return _Unit;
}
}
}
Also note that I did not change the value at all, hence:
var x = new Quantity(1700, "K");
means 1700K, not 1.7K. I would refrain from doing such "automagical" interpretations of data. If you need to display the value with a different unit, I would instead build in a conversion system:
public Quantity ConvertToUnit(string newUnit)
{
var newValue = ... calculate value with new unit
return new Quantity(newValue, newUnit);
}
The class is not a good design. Do not do this.
Consider the following code:
Quantities q1 = new Quantities { Unit = "K", Quant = 1000};
Console.WriteLine(q1.Quant); // Prints 1
// Make a copy of q1
Quantities q2 = new Quantities{ Unit = q1.Unit, Quant = q1.Quant };
Console.WriteLine(q2.Quant); // Prints 0
You would expect that making a copy of the Quantities would work by doing a basic copy like the above. That it does not shows you how dangerous this kind of design is.
This is still a problem after making the changes in the accepted answer above
If you use the changes that Daniel suggested, you still have the nastyness associated with your property setter and getter not being commutative. Sure, you would be forced to pass the units into the constructor, but the object copy still won't work as the user might expect:
Quantities q1 = new Quantities("K"){ Quant = 1000};
Console.WriteLine(q1.Quant); // Prints 1
// Make a copy of q1
Quantities q2 = new Quantities(q1.Unit){ Quant = q1.Quant };
Console.WriteLine(q2.Quant); // STILL Prints 0
Related
I am storing a int in schadstoffklasse so when calling the Car object like so (last int in brackets) :
PKW Kaefer = new PKW("VW", "Käfer", "K-GS-01", 1965, 9999, 1000, 30, 1);
I can either say 0, 1, 2.
Now when i write this Console.WriteLine(Kaefer.Schadstoffklasse)
to the console it obiously outputs 1 in this case.
I do want it to not say 1 i want for example....
0 = foo
1 = bar
2 = foobar
So it outputs to the console a string.
Here is what i have tried, which does not work.
private int schadstoffklasse;
public int Schadstoffklasse
{
get
{
return schadstoffklasse;
}
set
{
if (value == 0)
{
string foo = value.ToString();
foo = "BLABLALBA";
}
schadstoffklasse = value;
}
}
Thank you for having patience with a beginner
You can't have a property return mixed types. Your property of Schadstoffklasse is an int, therefore it can only ever return an int never a string.
There are a variety of different ways to accomplish this though, but without knowing more of how you are using this it'd be impossible to say which one you should do. I'd recommend either another property that has no setter and the getter looks at the other property, reads it's value and returns the string that you want or a method that does the same.
To expand on my suggestion:
public enum SchadstofklasseStrings
{
foo = 0,
bar = 1,
foobar = 2
}
public int Schadstoffklasse { get; set; }
public string SchadstoffklasseToString {
{
get
{
var stringValue = (SchadstofklasseStrings) Schadstoffklasse;
return stringValue.ToString();
}
}
Also, sorry for mutilating the German.
You can't change the type of a variable from int to string .
in this case i would create an array
["foo","bar","foobar"]
and use value of schadstoffklasse as an index
Console.WriteLine(Kaefer.myArray[Schadstoffklasse]);
Try this
private int schadstoffklasse;
public object Schadstoffklasse
{
get
{
if(this.schadstoffklasse==0)
return "foo";
if(this.schadstoffklasse==1)
return "bar";
if(this.schadstoffklasse==2)
return "foobar";
return "N/A";
}
set
{
this.schadstoffklasse=(int)value;
}
}
Note: The explain from user #gilliduck is useful. Consider this just
as a situational workaround.
I find enum helpful in situations like this since it is a collection of named integers. This is one example of how I might handle it.
void Main()
{
var Kaefer = new PKW("VW", "Käfer", "K-GS-01", 1965, 9999, 1000, 30, Schadstoffklassen.Bar);
Console.WriteLine(Enum.GetName(typeof(Schadstoffklassen), Kaefer.Schadstoffklasse));
// Output: Bar
}
public class PKW
{
private Schadstoffklassen schadstoffklasse;
public PKW(string v1, string v2, string v3, int v4, int v5, int v6, int v7, Schadstoffklassen _schadstoffklasse) {
schadstoffklasse = _schadstoffklasse;
}
public Schadstoffklassen Schadstoffklasse
{
get { return schadstoffklasse; }
set { schadstoffklasse = value; }
}
}
public enum Schadstoffklassen {
Foo = 0,
Bar = 1,
FooBar = 2
}
I am using a session helper class to track more than several variable. So far I have 30 that are needed from page to page, not all at once of course. I need to convert some of the values from single to array. The Session helper class I use is as follows. For brevity I have shown only two session variables we use for tracking tab index for two accordions.
using System;
using System.Globalization;
using System.Linq;
using System.Web;
public class SessionHelper
{
//Session variable constants
public const string AccordionTop = "#tabTop";
public const string AccordionBot = "#tabBot";
public static T Read<T>(string variable)
{
object value = HttpContext.Current.Session[variable];
if (value == null)
return default(T);
else
return ((T)value);
}
public static void Write(string variable, object value)
{
HttpContext.Current.Session[variable] = value;
}
public static int TabTop
{
get
{
return Read<int>(AccordionTop);
}
set
{
Write(AccordionTop, value);
}
}
public static int TabBot
{
get
{
return Read<int>(AccordionBot);
}
set
{
Write(AccordionBot, value);
}
}
}
So on each page I can work with variables easily as follows:
To Write:
SessionHelper.TabTop = 1; or SessionHelper.TabBot = 3
To Read:
If (SessionHelper.TabTop……….)
This all works fine. I now want to extend this to array values held in session. The array contains int, string and date time value.
For the array session object I have tried adding:
public class SessionHelper
{
public const string CompInfo = "CompAccInfo";
public static T ReadArray<T>(string variable)
{
object[] result = HttpContext.Current.Session[variable] as object[];
if (result == null)
{
return default(T);
//result = new object[30];
}
else
return ((T)(object)result);
}
public static void WriteArray(string variable, object[] value)
{
HttpContext.Current.Session[variable] = value;
}
public static object[] CompDetails
{
get
{
return ReadArray<object[]>(CompInfo);
}
set
{
WriteArray(CompInfo, value);
}
}
}
But then I get an “Object reference not set to…… error when I try to do this:
public void EGetCompanyInformation(MasterPage myMaster, int entityCode)
{
int prevEntity = 0;Using (sqlconnetiooo
.....
//I get values here this works fine
//Then:
sqlr = cmd.ExecuteReader();
sqlr.Read();
if (sqlr.HasRows)
{
//Calculate accounting period adjustment.
yearEndDiff = 12 - Convert.ToInt32(sqlr.GetDateTime(5).Month);
//Company Code.
SessionHelper.CompDetails[0] = sqlr.GetInt32(0);
//Company Name.
SessionHelper.CompDetails[1] = sqlr.GetString(1);
//Currency Unit.
SessionHelper.CompDetails[2] = sqlr.GetString(2);
//Base Currency Code.
SessionHelper.CompDetails[3] = sqlr.GetString(3);
//Reporting Currency Code.
SessionHelper.CompDetails[4] = sqlr.GetString(4);
//Company Year End.
SessionHelper.CompDetails[5] = yearEndDiff;
//Country Code.
SessionHelper.CompDetails[6] = sqlr.GetString(6);
//Country Name.
SessionHelper.CompDetails[7] = sqlr.GetString(7);
//Base Currency Name.
SessionHelper.CompDetails[8] = sqlr.GetString(8);
//Report Currency Name.
SessionHelper.CompDetails[9] = sqlr.GetString(9);
//ClientID.
SessionHelper.CompDetails[10] = sqlr.GetInt32(10);
Other code here
}
}
It seems any SessionHelper.CompDetails[i] does not work : Error Object reference not set to an instance of an object.
What will happen if ReadArray will return default(T)? It will return null. Than access to any object by index inside the array will cause the exception you face.
It is not quite obvious what your code is intended to do.
SessionHelper.CompDetails[0] = sqlr.GetInt32(0);
What do you want here? CompDetails itself should return an array. But you are trying to rewrite it immediately by some values.
If you want to access the CompDetails and rewrite it's objects than you have to instantiate it by
int n = 10;
SessionHelper.CompDetails = new CompDetails[n];
default(object[]) will always throw null. because the array of object is reference type and default value of any reference type is null. So accessing null value will get you Object reference not set to an instance of object.
You can change your old implementation like below:
public static T Read<T>(string variable, int arraySize=10)
{
object value = HttpContext.Current.Session[variable];
if(typeof(T).IsArray && value == null)
{
//array requires size I personally prefer to have
//differnt read method for array.
return ((T)Activator.CreateInstance(typeof(T),arraySize));
}
if(!typeof(T).IsValueType && value == null)
{
//if it is not value type you can return new instance.
return ((T)Activator.CreateInstance(typeof(T)));
}
else if (value == null)
return default(T);
else
return ((T)value);
}
And access SessionHelper as below:
var sessionarray = SessionHelper.Read<object[]>("myarray",15);
....
// then use that sessionarray here.
....
You have to instantiate the CompDetails array before you start assigning values to it.
if (sqlr.HasRows)
{
//Calculate accounting period adjustment.
yearEndDiff = 12 - Convert.ToInt32(sqlr.GetDateTime(5).Month);
// Instantiate array
SessionHelper.CompDetails = new object[11];
//Company Code.
SessionHelper.CompDetails[0] = sqlr.GetInt32(0);
// etc
I currently have a listbox that displays the date, type of cake and size. I want to add cost to the listbox, but I am having trouble. It currently displays zero for the cost. The cost is displayed in a label (lblRoundCost). I have a base class named Cake and two subclasses RoundCake and SquareCake. I'm not sure if this code is correct for the base class:
class Cake
{
private const int CostOfFoodPerPerson = 25;
public int size;
private bool chocolateIcing;
protected DateTime cakeDate;
decimal cost;
public Cake(int numberOfPeople, bool chocolateIcing, DateTime cakeDate)
{
this.chocolateIcing = chocolateIcing;
Size = size;
this.cakeDate = cakeDate;
Cost = cost;
}
public virtual decimal Cost
{
get { return cost; }
set { cost = value; }
}
public virtual int Size
{
get { return size; }
set { size = value; }
}
public virtual bool ChocolateIcing
{
set { chocolateIcing = value; }
}
public virtual decimal CalculateCost()
{
decimal CostOfIcing = 0;
if (chocolateIcing)
CostOfIcing = (Size * 1.5M) + 10M;
else
CostOfIcing = 0;
decimal TotalCost = CostOfIcing + CostOfFoodPerPerson;
return TotalCost;
}
public DateTime CakeDate
{
set { cakeDate = value; }
}
}
}
RoundCake code
class RoundCake : Cake
{
bool fruitOption;
public RoundCake(int size, bool fruitOption, bool chocolateIcing, DateTime cakeDate)
: base(size, chocolateIcing, cakeDate)
{FruitOption = fruitOption;}
public bool FruitOption
{
set { fruitOption = value; }
}
public override decimal CalculateCost()
{
decimal totalCost;
if (fruitOption)
{
totalCost = base.CalculateCost();
return totalCost + (totalCost * .05M);
}
else
{
totalCost = base.CalculateCost() ;
return totalCost;
}
}
public override string ToString()
{
return String.Format("{0,-20}{1,2}{2,20}{2,20}", cakeDate.ToShortDateString(), "RC",Size,Cost);
}
Form1 code
private void btnRound_Click_1(object sender, EventArgs e)
{
lstCake.Items.Add(roundCake);
}
roundCake = new RoundCake((int)nudRound.Value, chbFruit.Checked, chbChocoRound.Checked,
dtpRound.Value.Date);
lblRoundCost.Text = roundCake.CalculateCost().ToString("c");
The reason you're seeing 0 is because you never actually assign anything to Cost, and the default for decimal is 0.
Here's what's happening:
In your base constructor, you have:
Cost = cost;
However, cost is never initialized in the class and it's not passed in via the constructor. So in the base it's 0.
The same thing happens with the inheriting class - Cost is never specified, so it's still going to be 0 (even if there wasn't a base class, it'd still be 0).
Now, in this line of code:
lblRoundCost.Text = roundCake.CalculateCost().ToString("c");
You're assigning the value calculated by CalculateCost() to the Label, but you're never persisting that value in the the class:
public override decimal CalculateCost()
{
decimal totalCost;
if (fruitOption)
{
totalCost = base.CalculateCost();
return totalCost + (totalCost * .05M);
}
else
{
totalCost = base.CalculateCost() ;
return totalCost;
}
}
You're returning a value, but not assigning it to the class member cost. The base implementation does the same thing.
There a number of ways to solve this. Here's one (this is a pretty simple one, and to be honest it has a bit of a code smell to me, but it'll server as an example):
Modify the CalculateCost() method to update the cost field:
public virtual void CalculateCost()
{
decimal CostOfIcing = 0;
if (chocolateIcing)
CostOfIcing = (Size * 1.5M) + 10M;
else
CostOfIcing = 0;
decimal cost = CostOfIcing + CostOfFoodPerPerson;
}
Note that this doesn't return a type anymore (you may have it still do so, it really depends a lot on your overall design, so pick the path that works best for your design). Don't forget to make this change in the inheriting class's implementation as well.
Now you simply need to call the CalculateCost() method and you will have the cost available, and you can use the property to get the cost for assignment to Labels or whatever else you need, and it will show up in your overridden ToString() method.
Again, there are multiple ways to solve this, and they depend on a mix of OOP principles and your design needs. My main intention with this answer was to demonstrate why cost was showing up as zero.
I was looking for a similar way to create an alias for something else like its possible in C using preprocessor (this question is a bit similar, couldn't find anything useful there).
This is the problem: I've got a method that receives an array, but each position of the array has a specific meaning, like they where different parameters with specific names. What I want to do is to make my code easier to read (and write) by using those specific names, but, on the other hand, I don't want to create another method call (like in example 1) nor assign the array positions to new variables (example 2), because the performance is critical.
Example 1:
void OriginalMethodSignature(Type[] values)
{
SimplifiedMethod(values[0], values[1], ... values[n]);
}
void SimplifiedMethod(Type specificName1, Type specificName2, ... Type specificNameN)
{
// simple implementation using specific names instead of values[n]
}
Example 2:
void OriginalMethodSignature(Type[] values)
{
Type specificName1 = values[0];
Type specificName2 = values[1];
...
Type specificNameN = values[n];
// simple implementation using specific names instead of values[n]
}
I cannot change the method signature because its used in a dellegate, the Type is fixed.
The next example is a bit better, but still not optimum:
void OriginalMethodSignature(Type[] values)
{
// implementation using values[specificName1] ... values [specificNameN]
}
const int specificName1 = 0;
const int specificName2 = 1;
...
const int specificNameN = n-1;
Is there any way to create an snippet for this purpose? If yes, how would it be?
There isn't any built in way to do what you wan't, because you shouldn't really be doing it at all. You should be using an object with properties instead of an array.
Anyway, you can make an object that encapsulates the array, so that the properties use the array as storage:
public class NamedObject {
private Type[] _values;
public NamedObject(Type[] values) {
_values = values;
}
public SpecificName1 { get { return _values[0]; } set { _values[0] = value; } }
public SpecificName2 { get { return _values[1]; } set { _values[1] = value; } }
public SpecificName3 { get { return _values[2]; } set { _values[2] = value; } }
public SpecificName4 { get { return _values[3]; } set { _values[3] = value; } }
public SpecificName5 { get { return _values[4]; } set { _values[4] = value; } }
public SpecificName6 { get { return _values[5]; } set { _values[5] = value; } }
}
Now you can use the object to access the array:
void OriginalMethodSignature(Type[] values) {
NamedObject obj = new NamedObject(values);
// get a value
Type x = obj.SpecificName4;
// set a value
obj.SpecificName2 = x;
}
Create a dedicated class or struct, and parse the array into it.
public class MyClassOfStuff
{
Type SpecificName1 {get;set;}
Type SpecificName2 {get;set;}
public static MyClassOfStuff Parse(Type[] value)
{
Type specificName1 = values[0];
Type specificName2 = values[1];
...
Type specificNameN = values[n];
}
}
void OriginalMethodSignature(Type[] values)
{
var mystuff = MyClassOfStuff.Parse(values);
}
Consider these properties,
double _temperature;
public double Temperature
{
get { return _temperature; }
set { _temperature = value; }
}
double _humidity;
public double Humidity
{
get { return _humidity; }
set { _humidity = value; }
}
bool _isRaining;
public bool IsRaining
{
get { return _isRaining; }
set { _isRaining = value; }
}
And now I want to make a list/collection/container of properties like this,
PropertyContainer.Add(Temperature); //Line1
PropertyContainer.Add(Humidity); //Line2
PropertyContainer.Add(IsRaining); //Line3
I want to make this such that later on I may be able to access the current values of properties using index, something like this,
object currentTemperature = PropertyContainer[0];
object currentHumidity = PropertyContainer[1];
object currentIsRaining = PropertyContainer[2];
But obviously, this is not going to work, since PropertyContainer[0] will return the old value - the value which Temperature had at the time of adding Temperature to the container (see the Line1 above).
Is there any solution to this problem? Basically I want to access current values of properties uniformly; the only thing that can change is, the index. The index however could be string as well.
PS: I don't want to use Reflection!
Well, you could use Lambdas:
List<Func<object>> PropertyAccessors = new List<Func<object>>();
PropertyAccessors.Add(() => this.Temperature);
PropertyAccessors.Add(() => this.Humidity);
PropertyAccessors.Add(() => this.IsRaining);
then you could to this:
object currentTemperature = PropertyAccessors[0]();