class SomeClass
{
private struct PhraseInfo
{
public int Start;
public int Length;
}
...
private void SomeMethod(...)
{
List<PhraseInfo> posesBracket = new List<PhraseInfo>();
posesBracket.Add(new PhraseInfo());
posesBracket[0].Start = 10;
}
of cause, posesBracket[0].start=10; occur compiler error CS1612 : "Cannot modify the return value of 'expression' because it is not a variable"
how can i modify a value in list?
The problem is that PhraseInfo is a value type, so the this[] method will return a value, not a reference, to solve it, do this:
PhraseInfo pi = posesBracket[0];
pi.Start = 10;
posesBracket[0] = pi;
var temp = posesBracket[0];
temp.Start = 10;
posesBracket[0] = temp;
You cannot have a struct defined as a method. And as they say, you need the reference to change values. So it goes like this:
class SomeClass
{
private struct PhraseInfo
{
public int Start;
public int Length;
}
private void somemethod()
{
List<PhraseInfo> posesBracket = new List<PhraseInfo>();
posesBracket.Add(new PhraseInfo());
PhraseInfo pi = posesBracket[0];
pi.Start = 10;
posesBracket[0] = pi;
}
}
Related
Thanks to the kind folks who answered my previous question from a few days ago, I now know how to pass arguments by reference:
static void Main()
{
int i = 0;
Add(ref i, 100);
// now i == 100
}
static void Add(ref int arg, int increment)
{
arg += increment;
}
But is there a way for me not to just pass i by reference, but actually store its location in another variable? By that I mean use i like I did in my example; affecting the original instance, but in a way that's permanently linked and not leaving scope.
I vaguely know that I could use a pointer to determine the location in unsafe context but I was wondering if I could do this without any of that, or if it is just recommended to use the unsafe method.
If you are using C# 7 you can use ref local and ref return to store an updateable reference to any field.
In this example I change the private field _privateField from 0 to 100 from outside Foo, the class in which it is defined, by returning it as a ref int and updating it by reference.
class Foo
{
private int _privateField = 0;
public ref int GetReference()
{
return ref _privateField;
}
public override string ToString()
{
return _privateField.ToString();
}
}
public class Program
{
public static void Main()
{
var foo = new Foo();
var referenceToPrivateField = foo.GetReference();
referenceToPrivateField = 100;
Console.WriteLine(foo);
}
}
Prior to that, you'd have to store the value in a field contained in an object, and pass around a reference to the object instead.
In this example I change the value from 0 to 100 from outside Foo, even though it is stored (indirectly) in a field that is private inside the Foo instance.
class ValueTypeReference<T> where T : struct
{
public T Value { get; set; }
}
class Foo
{
private ValueTypeReference<int> _privateField = new ValueTypeReference<int>{ Value = 0 };
public ValueTypeReference<int> GetReference()
{
return _privateField;
}
public override string ToString()
{
return _privateField.Value.ToString();
}
}
public class Program
{
public static void Main()
{
var foo = new Foo();
var referenceToPrivateField = foo.GetReference();
referenceToPrivateField.Value = 100;
Console.WriteLine(foo);
}
}
Output:
100
Well, if I udnerstood you correctly, you want the variable to have global scope, which can be achieved by putting variable as class field/property:
class Program
{
private static int _i;
static void Main()
{
_i = 0;
Add(100);
// now _i == 100
}
static void Add(int increment)
{
_i += 100;
}
}
I have 2 ref classes in C++/CLI:
>The first class:
public ref class wBlobFilter
{
int mMin;
int mMax;
bool mIsActive;
public:
// min value
property int Min
{
int get() {return mMin;}
void set(int value) {mMin = value;}
}
// max value
property int Max
{
int get(){return mMax;}
void set(int value){mMax = value;}
}
// set to true to active
property bool IsActive
{
bool get() {return mIsActive;}
void set(bool value){mIsActive = value;}
}
};
>The second class:
public ref class wBlobParams
{
wBlobFilter mFilter;
public:
property wBlobFilter Filter
{
wBlobFilter get() {return mFilter;}
void set(wBlobFilter value) { mFilter = value; }
}
};
when I call it in C# I got an error message : "Cannot modify the return value because it is not a variable"
Params.Filter.Min = 0;
So, how can I set the value of the member variable of class wBlobFilter through class wBlobParams's property directly ? Sorry for my bad English. Thank you!!!
It's hard to know what exactly you want to happen. If it inherits then the properties from the filter will be available.
public ref class wBlobParams : public wBlobFilter
{};
void f(wBlobParams^ params) {
auto max = params->Max;
}
Or replicate the property access in wBlobParams:
public ref class wBlobParams {
public:
wBlobFilter^ mFilter;
property int Max {
int get() { return mFilter->Max; }
}
};
void f(wBlobParams^ params) {
auto max = params->Max;
}
Edit 1:
Look at this. What you were doing was fine. Just your syntax for using gc handles is wrong.
public ref class cA {
int x;
public:
cA() : x(0) {}
property int X {
int get() { return x; }
void set(int _x) { x = _x; }
}
};
public ref class cB {
cA^ a;
public:
cB() : a(gcnew cA()) {}
property cA^ A {
cA^ get() { return a; }
void set(cA^ _a) { a = _a; }
}
};
void main() {
cB^ b = gcnew cB();
b->A->X = 5;
Console::WriteLine(b->A->X);
}
So I got this base class
abstract class Item
{
private int x, y, ataque, defesa, saude, raridade;
private char appearance;
private bool pickedUp;
private readonly Random rng = new Random();
public Item(Map argMap, int argAtaque, int argDefesa, int argSaude, int argRaridade, char argAppearance)
{
bool empty = false;
while (!empty)
{
x = rng.Next(1, argMap.ReLengthX() - 1);
y = rng.Next(1, argMap.ReLengthY() - 1);
if (!argMap.CheckTile(y, x)) empty = true;
}
pickedUp = false;
ataque = argAtaque;
defesa = argDefesa;
saude = argSaude;
raridade = argRaridade;
appearance = argAppearance;
}
}
And I got this derived class
class Armadura : Item
{
public Armadura(Map argMap, int ataque, int defesa, int saude, int raridade, char appearance) : base(argMap, ataque, defesa, saude, raridade, appearance)
{
ataque = -1;
defesa = 2;
saude = 0;
raridade = ReRNG().Next(Convert.ToInt32(Math.Round(argMap.ReLengthY() * 0.02)), Convert.ToInt32(Math.Round(argMap.ReLengthY() * 0.04)));
appearance = ' ';
}
}
So my question is, how do I get to set the values on :base, using the values that I set on the derived constructor (for example, set the base argAtaque with ataquewwww, therefore, argAtaque being equal to '-1')?
I tried this using a few ways but I didn't get this to work in any way.
I thank you in advance!
The : base() syntax will work for constants and parameters, but not for more complex expressions with side-effects (as you found).
You'll be needing a initialization method on the base class.
abstract class Item
{
...
// If you use this constructor, call Setup() afterwards.
public Item() {}
// Constructor including a call to Setup()
public Item(Map argMap, int argAtaque, int argDefesa, int argSaude, int argRaridade, char argAppearance)
{
Setup(argMap, argAtaque, argDefesa, argSaude, argRaridade, argAppearance);
}
// Sets private variables for this Item
protected void Setup(Map argMap, int argAtaque, int argDefesa, int argSaude, int argRaridade, char argAppearance)
{
bool empty = false;
while (!empty)
{
x = rng.Next(1, argMap.ReLengthX() - 1);
y = rng.Next(1, argMap.ReLengthY() - 1);
if (!argMap.CheckTile(y, x)) empty = true;
}
pickedUp = false;
ataque = argAtaque;
defesa = argDefesa;
saude = argSaude;
raridade = argRaridade;
appearance = argAppearance;
}
}
Now you can setup the base class with the calculated values:
class Armadura : Item
{
public Armadura(Map argMap)
{
int ataque = -1;
int defesa = 2;
int saude = 0;
int raridade = ReRNG().Next(Convert.ToInt32(Math.Round(argMap.ReLengthY() * 0.02)), Convert.ToInt32(Math.Round(argMap.ReLengthY() * 0.04)));
char appearance = ' ';
Setup(argMap, ataque, defesa, saude, raridade, appearance);
}
All you have to do is set ataque in the child constructor, as it will override what ataque is being set to in your base class. The base constructor is called first, then the child constructor.
For this to work, you will need to make your private variables protected in the base class. This will make them private in the child class.
I'm trying to compare an object with an int value such as
if (myObject - 5 == 0)
doSomething();
my class could look something like this: (most setters/getters removed, so don't mind that all variables are private)
public class SomeClass
{
public string name;
private int minValue;
private int maxValue;
private int currValue;
public int getCurrentValue()
{
return currValue;
}
}
What I'm trying to achieve is something like this:
someClassInstance - 5;
to be equal
someClassInstance.getCurrentValue() - 5;
Can I make an override for the object to act as an int (it's own variable) opposed to just being an object?
May be operator is the case?
public class SomeClass {
...
public static int operator -(SomeClass left, int right) {
if (Object.ReferenceEquals(null, left))
throw new ArgumentNullException("left");
return left.getCurrentValue() - right;
}
}
...
SomeClass someClassInstance = new SomeClass(...);
int result = someClassInstance - 5;
Another possibility (based on implicit operator) is to convert SomeClass implicitly to int whenever required:
public class SomeClass {
...
// Whenever int is requiered, but SomeClass exists make a conversion
public static implicit operator int(SomeClass value) {
if (Object.ReferenceEquals(null, value))
throw new ArgumentNullException("value");
return value.getCurrentValue();
}
}
...
SomeClass someClassInstance = new SomeClass(...);
int result = someClassInstance - 5;
Actually you would be much better off overriding operator int, that way you can do far more calculations with less overloads:
using System;
namespace Demo
{
public class SomeClass
{
public string name;
private int minValue;
private int maxValue;
public int currValue;
public int getCurrentValue()
{
return currValue;
}
public static implicit operator int(SomeClass value)
{
if (value == null)
throw new ArgumentNullException("value");
return value.currValue;
}
}
internal class Program
{
private void run()
{
var test = new SomeClass {currValue = 5};
if (test - 5 == 0)
Console.WriteLine("It worked");
if (test + 5 == 10)
Console.WriteLine("This also worked");
}
private static void Main()
{
new Program().run();
}
}
}
You could experiment with a mixture of implicit conversions and operator overloading, but from my experience you will never make it work as seamlessly as you wish (and as you could get it to work in C++).
If I were you, I would change the getCurrentValue to a property:
public int CurrentValue
{
get {return currValue};
}
and just use someClassInstance.CurrentValue -5
I have many constants I need to move around in one of my classes but I'm not allowed to use member variables. What are some options?
Here's my initial try:
private void MyConstants(out int textSize, out int paddingValue, out int borderType, ...)
{
//Set them here
}
private Method1()
{
int textSize = 0;
int paddingValue = 0;
int borderValue = 0;
....
MyConstants(out textSize, out paddingValue, out borderValue)
}
private Method2()
{
int textSize = 0;
int paddingValue = 0;
int borderValue = 0;
....
MyConstants(out textSize, out paddingValue, out borderValue)
}
//Many more methods...Just seems to repetitive.
Use Private Class or Struct.
private class Variables {
public int textSize;
public int paddingValue;
public int borderValue;
}
private Variables MyConstants{
get{ return new Variables(){textSize=1, paddingValue=2, borderValue=3};}
}
If you need to initialize in constructor try using readonly instead on const.
Edit 1:
You can create a class that holds a private Dictionary:like key and value.
put a "object LoadConstant(string)" method in it that will withdraw the data.
public static class ConstantManager {
private static Hashtable _consts = new Hashtable();
private static const keyName = "Name 1";
public static void ConstantManager()
{
_consts[keyName] = ...;
}
public static Hashtable GetConstants()
{
var _copy = new Hashtable(_consts);
return _copy;
}
}
public OtherClass{
public void Method()
{
var consts = ConstantManager.GetConstants();
var a = consts[ConstantManager.keyName];
}
}