C# How To Use Inovke

Managed code, such as C# or VB.NET, provides native access to classes, methods, and types defined within the libraries that make up the .NET Framework. P/Invoke is the technique a programmer can use to access functions in these libraries. Calls to functions within these libraries occur by declaring the signature of the unmanaged function within managed code, which serves as the actual function that can be called like any other managed method. There are many abstractions of lower level programming concepts available to managed code programmers as compared to programming in unmanaged languages. While I do feel that the article may be a bit biased its does present a lot of gotchas that new C# developers should keep and eye out for.

Some of the mistakes listed are not C# exclusive and avoidable by simply educating ones self on how the language behaves (ex. value vs reference, types). Some solutions need to be prefaced with "depending on the case". I also feel that the #9 may have missed the mark a little bit, they are there for catching errors IF one occurs and returning you to a "safe" place where you are able to safely recover.

However, it is correct in saying that exceptions should not be used as a normal control statement. Even though I know better, I too, am guilty of using them incorrectly from time to time. The mistake would also benefit from having a bit more on how to use exceptions correctly. LINQ like any language feature can be abused and used in such ways that it does make things harder to understand but it is a powerful tool that should not be overlooked. I like to use it when accessing data sources, and then prefer other control loops for any processing on the data.

This separates processing code from data access visually and helps keep things easy to spot and understand. LINQ allows for the ability to create complex "SQL like" statements that MAY be more difficult to implement in the SQL flavor of choice. LINQ vs Extension methods, it is key to keep your understanding of these clear. LINQ is not extension methods, LINQ is not Extension methods, LINQ is not extension methods. I have seen a lot of confusion about what the difference is here even though a lot of extension methods can do linq like things and they are OFTEN used together they are two very distinct language features.

Extension methods allow for extending types that you don't necessarily have access to, such as third party dll's. Linq is just really a syntactic sugar that allows for a different approach which may make things conceptually simpler to understand. For the large intersection of unmanaged code that doesn't have pass-by-value structures or return pointers to structures from functions?

Not all languages support passing types by reference , so using classes will permit a larger body of languages to use the wrapper library. Furthermore, Microsoft suggests that structure sizes not exceed 16 bytes. These differences permit structures to be passed by-value to unmanaged functions, unlike classes.

This means that you may not need to specify the Out attribute to see changes made by unmanaged code. The runtime is so cool, that it also allows communication to flow in both directions, meaning that you can call back into managed code from native functions by using function pointers! Now, the closest thing to a function pointer in managed code is a delegate, which is a type that represents references to methods with a particular parameter list and return type. And this is what is used to allow callbacks from native code into managed code.

By default, the P/Invoke subsystem tries to do type marshaling based on the default behavior. Simply, C# is a type-safe object-oriented language that enables developers to build a variety of secure and robust applications. It's syntax simplifies many of the complexities of C++ and provides powerful features such as nullable types, enumerations, delegates, lambda expressions, and direct memory access.

C# also runs on the .NET Framework, which is an integral component of Windows that includes a virtual execution system called the Common Language Runtime or CLR and a unified set of class libraries. The CLR is the commercial implementation by Microsoft of the Common Language Infrastructure known as the CLI. While there certainly are advantages to using extension methods, they can cause problems and a cry for C# programming help for those developers who aren't aware of them or don't properly understand them. This is especially true when looking at code samples online, or at any other pre-written code. A lot of time can be spent searching for a new version, or phantom "missing library", that doesn't exist. Both Invoke or BeginInvoke methods require a delegate object as a parameter.

The delegate is similar to the address of the callback function, so the caller can marshal the address of the function that needs to be called to the interface thread through these two methods. If these methods contain code that changes the state of the control, then the interface thread will eventually execute this method, thereby avoiding race conditions and avoiding unforeseen problems. If other threads directly manipulate the controls to which the interface thread belongs, then race conditions will occur, causing unpredictable results.

The first one holds a reference to an object, and the second holds a method pointer. When you invoke the delegate, the instance method is called on the contained reference. However, if the object reference is null then the runtime understands this to mean that the method is a static method. Moreover, invoking a delegate syntactically is the exact same as calling a regular function. Therefore, delegates are perfect for implementing callbacks.

If string were used instead, Bad Things could happen (the returned string would be freed; see Strings as Return Values ). The StringBuilder is allocated with the correct amount of storage as a constructor parameter, and this amount of storage is passed to strncpy to prevent buffer overflow. For simple types, such as integers and floating-point numbers, marshaling is a bitwise-copy ("blitting"), just as would be the case for unmanaged code.

In some cases, marshaling can be avoided, such as when passing structures by reference to unmanaged code . It's also possible to obtain more control over marshaling, through custom marshaling and manual marshaling. You define a Lambda function handler as an instance or static method in a class. For access to the Lambda context object, you can define a method parameter of type ILambdaContext. You can use this to access information about the current invocation, such as the name of the function, memory limit, remaining execution time, and logging. Listing 5.33 demonstrates the assignment of an anonymous type to an implicitly typed local variable.

When the compiler encounters the anonymous type syntax, it generates a class with properties corresponding to the named values and data types in the anonymous type declaration. Although there is no available name in C# for the generated type, it is still statically typed. For example, the properties of the type are fully accessible. In Listing 5.33, patent1.Title and patent2.YearOfPublication are called within the Console.WriteLine() statement. Any attempts to call nonexistent members will result in compile-time errors.

Even IntelliSense in IDEs such as Visual Studio works with the anonymous type. When a C# program is executed, the assembly is loaded into the CLR, the CLR then performs Just-In-Time compilation to convert the IL code to native machine instructions. The CLR also provides other services such automatic garbage collection, exception handling, and resource management. Code that's executed by the CLR is sometimes referred to as "managed code", in contrast to "unmanaged code", which is compiled directly into native machine code for a specific system.

"I saw the LINQ statement first and I totally got what it was doing immediately" — it means you saw simple LINQ statements, in the cases where the decision to use LINQ was wise. You cannot step in/step over, which becomes problem e.g. if the LINQ contains non-MS extension methods — you can't just step in to find out what it does. You cannot use intermediate IDE window with statements that have lambdas. Unlike imperative code, you can't review intermediate results as they're not kept in variables but lost in the call stack.

Intermediate data is very often implicitly typed and unnamed. I saw a funny article entitled "What if Visual Studio had Achievements? The relevant item is #2 that says "Job Security – Written a LINQ query with over 30 lines of code". In my previous comment, I was talking about _that_ kind of LINQ. You can see that ISynchronizeInvoke has an attribute, InvokeRequired. This property is used to determine when programming, whether an object needs to use Invoke or BeginInvoke for marshaling when accessing UI controls.

This property returns false when the caller object and the UI object belong to the same thread. In the following code analysis, we can see that the realization of this attribute of the Control class is to determine whether the caller and the control belong to the same thread. As with all object-oriented libraries, there can be an unknown number of derived classes, each of which having a different class size. Furthermore, class instances are typically accessed through pointers.

As such, marshaling the entire class between managed and unmanaged memory is not an option, as a copy isn't desired, access to the same instance is. The key in the following tutorial is System.Runtime.InteropServices, where we can find the Marshal class. That class is very useful because it bridges created managed objects and unmanaged ones. Its functionalities are very similar to blocks, unsafe, and more.

For example, let's say that all pointer types in .NET are saved in an instance of the type IntPtr. With the Marshal class, we can perform any operation like adding a determined number of bytes in order to point to other objects, and converting things that are there in a structure or a chain . There are two primary differences between classes and structures. First, structures do not need to be allocated on the heap; they can be allocated on the runtime stack. Secondly, they are LayoutKind.Sequential by default, so structure declarations do not need any additional attributes to use them with unmanaged code . If you don't want the runtime to search for the alternate unmanaged functions, specify a CharSet value other than CharSet.Auto.

This will cause the runtime to look only for the specified function. Note that if you pass a wrongly encoded string (e.g. calling MessageBoxW when the CharSet is CharSet.Ansi, the default), you are crossing into "undefined" territory. The unmanaged function will receive data encoded in ways it wasn't expecting, so you may get such bizarre things as Asian text when displaying "Hello, World". If handler is a pointer to a managed delegate which may throw an exception, then free will not be executed, resulting in a memory leak. Furthermore, it's fairly simple for an exception to propagate through unmanaged code whenever unmanaged code invokes managed code. This typically occurs through the use of callbacks – using a function pointer on the unmanaged side which can invoke a delegate on the managed side.

It is very important that the managed code not propagate any exceptions – it must catch all exceptions, or else the unmanaged code calling the delegate will break. Protocol buffers are the flexible, efficient, automated solution to solve exactly this problem. With protocol buffers, you write a .proto description of the data structure you wish to store.

From that, the protocol buffer compiler creates a class that implements automatic encoding and parsing of the protocol buffer data with an efficient binary format. The generated class provides getters and setters for the fields that make up a protocol buffer and takes care of the details of reading and writing the protocol buffer as a unit. Importantly, the protocol buffer format supports the idea of extending the format over time in such a way that the code can still read data encoded with the old format. For my money, the simplest method is to simply call the InvokeAsync method from the View's Component property, passing the name of your view component and its parameters.

You must use the await keyword here to ensure that your Task object is resolved before your View finishes processing. If you omit the await keyword Razor will shove the string representation of the Task object returned by the InvokeAsync method into your page. Constructors define what happens during the instantiation process of a class.

To define what happens when an object is destroyed, C# provides the finalizer construct. Unlike destructors in C++, finalizers do not run immediately after an object goes out of scope. A separate thread runs through each object in the finalization queue and calls the object's finalizer before removing it from the queue and making it available for the garbage collector again. Chapter 9 discusses this process, along with resource cleanup, in depth. Parameters - If the method or constructor represented by this instance takes a ref parameter , no special attribute is required for that parameter in order to invoke the method or constructor using this function.

Any object in this array that is not explicitly initialized with a value will contain the default value for that object type. For value-type elements, this value is 0, 0.0, or false, depending on the specific element type. As discussed, we can extend the behavior of classvariablesusing propertiesgetandsetaccessors. Following is the example of extending the behavior of privatevariablein property usinggetandsetaccessors in c# programming language.

Invoking multiple methods by one delegate may lead into a problematic situation. If one of the methods invoked by a delegate throws an exception, then the complete iteration would be aborted. You can avoid such a scenario by iterating the method invocation list on your own. The Delegate class defines a method GetInvocationList that returns an array of Delegate objects. Generally, the answer to this question depends upon what the unmanaged code requires.

If you require pass-by-value semantics, you must use structures. If you want to return a pointer to an unmanaged type without resorting to "unsafe" or manual code, you must use classes . When TextOut is called, the "magic" properties of String marshaling become apparent.

Due to string marshaling, the runtime doesn't just look for an unmanaged function with the same name as the specified method, as specified in Invoking Unmanaged Code. Other permutations of the function may be searched for, depending on the CLI runtime and the host platform. As stated before, Marshaling is the process of transforming types when they need to cross between managed and native code. Marshaling is needed because the types in the managed and unmanaged code are different as we've already seen and demonstrated. C# continues its enforcement of type safety into runtime. This allows you to pinpoint many types of errors in C# much more quickly than in languages such as C++, where faulty type conversions can result in arbitrary values being assigned to an object's fields.

However, once again, programmers can squander this great feature, leading to C# problems. They fall into this trap because C# provides two different ways of doing things, one which can throw an exception, and one which won't. Some will shy away from the exception route, figuring that not having to write a try/catch block saves them some coding.