Wanted to know how to get caller information for a property
for a method it is easy
public void TraceMessage([CallerMemberName] string memberName = "") {
Console.Println(memberName);
}
and you will get who called the method.
I want the same thing for a property
public MySqlConnection Connection { get; set; }
I tried getting the caller name by calling a function from the getter like this
public Connection connection { get { TraceMessage()
return _someVariable;}
set; }
But by doing this the TraceMessage prints
Connection
as the method name
Is there any way to either pass a parameter to the getter or something else to achieve this?
You get the name of the property because it is the previous method in the stack trace. To trace it in the property you can use System.Diagnostics.StackTrace:
using System.Diagnostics;
.
.
public Connection connection
{
get
{
Console.WriteLine(new StackTrace().GetFrame(1).GetMethod().Name);
return _connection;
}
}
Example can be found in this link
Furthermore if you want to create a separate method for that you can create a method that gets the frame before the frame. The frames are indexed so that current method/property frame is 0, the caller is 1, caller of the caller is 2 and so forth.
public void LogCaller()
{
Console.WriteLine(new StackTrace().GetFrame(2).GetMethod().Name);
}
And then call that method from the property.
Related
I'm working with some C# code that's using .Net 4 Lazy loads and I'm not super familiar with it. I'm trying to figure out if this particular code is useless or not.
Originally the property and code below where in the same class, but now I've moved the code to an external class that no longer has access to the private "lazyRecords" property. I'm wondering what the point of checking "lazyRecords.IsValueCreated" is since the lazyRecords.Value has not been invoked yet, wouldn't it always be false? Or is it checking to see if another thread somehow invoked the Value? Or is it doing this in case of a thread exception that resulted in not loading the object?
Property:
private Lazy<List<Record>> lazyRecords;
public List<Record> Records
{
get
{
return lazyRecords.Value;
}
set
{
lazyRecords = new Lazy<List<Record>>(() => value);
}
}
Code:
public Category LoadCategory(BaseClient client)
{
Category category = new Category();
category.Records = client.RecordClient.GetRecordsByCategoryID(category.ID);
if (lazyRecords.IsValueCreated)
{
category.WorldRecord = category.Records.FirstOrDefault();
}
else
{
category.WorldRecord = client.RecordClient.GetWorldRecord(category.ID);
}
}
The code is pretty useless, yes. To help you understand why, consider this very minimal version of Lazy (the real class has more options and logic to take care of multiple threads, but this is the rough idea):
public class Lazy<T>
{
private readonly Func<T> _creator;
private T _cachedValue;
public Lazy(Func<T> creator) => _creator = creator;
public bool IsValueCreated { get; private set; }
public T Value
{
get
{
if (!IsValueCreated)
{
_cachedValue = _creator();
IsValueCreated = true;
}
return _cachedValue;
}
}
}
The delegate passed to the constructor is called on demand, the first time the Value is requested. In the code you've posted there is no point to this because the delegate simply returns the value passed into the setter.
As to the LoadCategory method, the code you posted is hard to decipher. It directly accesses lazyRecords, implying it's a method of the same class. But then it accesses Records on a different object.
I have a property with has an attribute, which in turn has Func<object, object>, I want that function to be executed (using the updated property's value as in T) upon the property change. What's the slickest way of doing so?
Note: I'm aware of the facts that Attributes are static and aren't designed to be executed upon their assignees change/invocaction. I just need to get it working as close as can to the prototype I've created.
Some code:
using System;
using System.Windows;
namespace AnnotatedBinding
{
public class AnnotatedPropertyAttribute: Attribute
{
// static
public AnnotatedPropertyAttribute(Func<object, object> evaluator)
{
Evaluator = evaluator;
}
public Func<object, object> Evaluator
{
get; private set;
}
}
public class Test
{
[AnnotatedProperty(Test.TestEvaluator)] // not compiling!, guess it's fixable by passing in a member info and then calling Reflection Invoke?
public string TestProperty
{
get; set;
}
public static Func<object, object> TestEvaluator = (x) => MessageBox.Show(x.ToString());
}
public class Shell
{
public void Run()
{
var test = new Test();
test.TestProperty = "blah";// I want my message box here
test.TestProperty = "blah";// and I don't want it here
}
}
}
Your attribute on the TestProperty does not compile because delegates are not allowed as attribute arguments. See this answer from Eric Lippert for details about which types are allowed.
Regarding a workaround using reflection: You could certainly specify the type owning the method, and the name of the method in the attribute since System.Type and string are valid attribute argument types. Something like this:
[AnnotatedProperty(typeof(Test), "TestEvaluator")]
public string TestProperty { get; set; }
However, this still won't do anything with the delegate when the property is set. Attributes are only metadata that you can read out during runtime using reflection (more specifically using MemberInfo.GetCustomAttributes(...)), analyse them and perform any operation based on the attribute values. This all needs to be done manually. Unfortunately, the .NET framework does not offer the functionality to automatically perform some operation based on the attributes that are applied to a member. This would make life a lot easier for property change notifications as well.
So you would have to implement the handling of the attributes manually. That means, implementing the get and set accessors, checking whether the attribute is applied to that property, determine the delegate that should be executed, and exeute it using reflection. Of course, that does not make sense because you would rather add a call to the method in the setter instead.
tl;dr:
Possible solution: You should have a look at PostSharp, a library supporting aspect-oriented programming in .NET. It can be used to inject boiler-plate code into methods or other members after compilation. It does this by analyzing your MSIL code and searching for so-called "aspects" (which are actually attributes, like yours). If found, it modifies the MSIL as specified by the attribute. You would have to derive your attribute from a PostSharp base attribute/aspect and then override the appropriate methods. In your case, you would have to derive from the LocationInterceptionAspect and then override the OnSetValue(...) method. In this method you would determine the delegate using the attribute arguments (as given above) and then call this using reflection. "Intercepting Properties and Fields" in the PostSharp documentation gives a very good introduction how to do this.
I think you would end up with something like this:
public class ExecuteDelegateOnPropertySetAspect : LocationInterceptionAspect
{
public ExecuteDelegateOnPropertySetAspect(Type methodOwner, string methodName, object[] arguments)
{
this.MethodOwner = methodOwner;
this.MethodName = methodName;
this.Arguments = arguments;
}
public Type MethodOwner { get; set; }
public string MethodName { get; set; }
public object[] Arguments { get; set; }
public override void OnSetValue(LocationInterceptionArgs args)
{
// get method with the specified name from the specified owner type
MethodInfo method = this.MethodOwner.GetMethod(this.MethodName);
// method must be static, otherwise we would need an instance to call it
if (method != null && method.IsStatic)
{
if (method.GetParameters().Length == this.Arguments.Length)
{
// call the method with the given arguments
method.Invoke(null, this.Arguments);
}
}
// execute the original setter code
args.ProceedSetValue();
}
}
And in your code you would apply this aspect to your properties:
public class Test
{
public static void TestMethod(string someMessage)
{
MessageBox.Show(someMessage);
}
[ExecuteDelegateOnPropertySetAspect(typeof(Test), "TestMethod", new object[] { "Hello world!" })]
public string TestProperty { get; set; }
}
Note that I omitted most of the error and null checking to keep it simple and short.
You seem to have misunderstood the concept of properties in C#.
The properties have a getter and setter function. They will automatically get executed when you set the property or get its value.
So all you need to do is to change the set function of your property to something like this:
public class Test
{
private string _testProperty;
private bool testPropertyIsSet = false;
public string TestProperty
{
get { return this._testProperty; }
set
{
_testProperty = value;
if (!testPropertyIsSet)
{
// Do something here when your property gets set for the first time
}
testPropertyIsSet = true;
}
}
}
Then call it:
public void Run()
{
var test = new Test();
test.TestProperty = "blah";
test.TestProperty = "blah2";
}
I'm working on setting up a login form for an existing application. I'm currently having issues with getting the value of one of the text boxes in a class.
For example Form9 has a textbox called txtchannel. I'm wanting to get the value of what's in txtchannel in the class.
// Revision
I was finally able to get it to take the command using the following
// Class
private void DoConnect()
{
try
{
jtvClient.Connect();
jtvClient.JoinChannel("#" + this.mainForm.txtChan.Text);
}
catch (Exception ex)
{
op.Post(x => OnExceptionThrown((Exception)x), ex); // TODO: double check that exceptions
} // actually show up at this level
}
private Login mainForm = null;
public JtvClient(Login derp)
{
mainForm = derp as Login;
}
////
This is allowing me to at the very least call the what is in Login(Now Formally Form9). However it gives an error "Object reference not set to an instance of an object.". I'm at a complete loss.
I think the Text property of the TextBox class is what you are looking for. See MSDN for the full documentation on TextBox.Text.
The best way to get the value in another class (if you mean another class), is to expose a property called Channel in Form9. The would look like this:
public string Channel
{
get
{
return txtChannel.Text;
}
}
I have a class with like 20 fields which get populated from SQL database on load. Currently I am calling load data method right after the constructor, which calls SQL proc and populate all the required fields. At times, I may not access the these 20 fields at all, I am adding additional cost of SQL call even though it was not required. So I changed all the properties to have an associated private property and when the program calls the public property, first I check the private property and if it is null that means we need to load data from sql so I call the load method. It works great, but when I see the code, there is a repeated pattern of null check and load the sql query. Is there a better way of doing this?
private string _name;
public string Name
{
get {
if (_name == null)
LoadData(); //this popultes not just but all the properties
return _name;
}
}
Btw C# now has default lazy-loaders implementation. Why not to use it, instead of providing isSomethingLoaded flags? :)
public class Bar
{
private Lazy<string> _name = new Lazy<string>(() => LoadString());
public string Name
{
get { return _name.Value; }
}
}
In case of non-static LoadString method, lazy-loader should be initialized in constructor;
Nope, this is right. Here is the wikipedia article. The overhead of the null check will be very minimal compared to unnecessary database calls. Now, if the users of the program actually use the values 99% of the time, then I would say this pattern is not needed.
Just one note of caution: If any of your values could possibly be null, then you will make unnecessary database calls. It might be better to do something like this (which will be an even quicker check since it is just a bit check):
//Constructor default to not loaded
bool isLoaded = false;
private string _name;
public string Name
{
get {
if (!isLoaded)
LoadData(); //this popultes not just but all the properties
return _name;
}
}
private LoadData()
{
//Load Data
isLoaded = true;
}
Well you could change it to:
if (!initialized)
LoadData();
And in your LoadData set initialized to true, but that really doesn't change the semantics of it.
One thing you can do is to extract if into separate method so each property contains just one additional call:
void EnsureData()
{
if (!dataLoaded)
LoadData(); //this populates all the properties
}
public string Name {
get {
EnsureData();
return _name;
}
}
I think you should consider your application structure. Why would you even instantiate the class if you are not going to be using the properties? I believe it's actually cleaner for you to call the SQL after your constructor code but only create the objects of your class if you are going to be using it. The other more flexible solution is making the LoadData public and calling it as needed from the object instance as needed.
I am in the learning process of design patterns. i have one suggestion if you load data only once you can try with singleton design pattern.
public class Singleton123
{
private static readonly string _property1 = ClassLoadData.LoadData();
public static string MyProperty1
{
get
{
return _property1;
}
}
}
public class ClassLoadData
{
public static string LoadData()
{
// any logic to load data
return "test";
}
}
Call property as below
Singleton123 obj = new Singleton123();
string stra = Singleton123.MyProperty1;
string strb = Singleton123.MyProperty1;
this property will be loaded only once.
I have a class that adds information to a list and then does some calculations. Now I want to return that to the original program. How do I do that?
In Main program I have public value
public string ResponseTime
{
get { return _ResponseTime; }
set { _ResponseTime = value; }
}
MAIN FUNCTION()
Within the main function I call the class which calculates the correct response time and returns it back. The question is how do I capture it in this main program?
ListTest.CalculateResponseTime(_ResponseTime); - need to use the value that returns and set ResponseTime to that value.
public static string CalculateResponseTime(string responseTime)
{
}
Are you just asking how to get the return value from a function??
ResponseTime = ListTest.CalculateResponseTime(_ResponseTime);
pass the parameter by reference
public void CalculateResponseTime(ref string responseTime)
{
// your code
}
you don't need to return the string, becuase when your modify the value of your string in the function ,the value will be modified the the original location (memory address) and not only in the scope of your function.
In this way you can assign directly the property of your class as function parameter, and when the function ends your property has the value modified too.
The alternative is passing your parameter as value and return the reult as assign of your property.
if you need more information about it. MSDN is your friend
ResponseTime = [insert calculated value]
(...at least, that's how I'm interpreting your question...)