COM Component Design and Application (5)

Use ATL to write the first component

Author: Instructor Yang

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I. Preface

1. If you are using vc5.0 or a previous version, upgrade it to vc6.0 or vc.net 2003;
2. If you are using vc6.0 (ATL 3.0), read this article;
3. If you are using vc.net (ATL 7.0), please read the next article. (Of course, reading this article is also good)
4. Except for the iunknown interfaces required by all COM components, the first component implements a self-defined interface ifun, which has two functions: add () completes the addition of two values, and CAT () completes the connection between the two strings.
5. Let's hear it! Started :-)

II,Create an ATL Project
Step 2.1: Create a workspace ).
Step 2.2: Create an ATL Project in the workspace ). The sample program is simple1 and the DLL method is selected. See figure 1.

Figure 1. Create an atl dll Project

　　Dynamic link library (DLL)Build a DLL component program.
　　Executable (exe)Indicates creating an EXE component program.
　　Service (exe)Indicates the establishment of a service program, and the program will be loaded and executed after the system starts.
　　Allow merging of proxy/stub codeIf this option is selected, the "Proxy/stub" code is merged into the component program. Otherwise, you must compile the Code separately and register the proxy stub program separately. Proxy/stub. What is this concept? Do you remember what we introduced in the previous book? When the caller calls the functions of external or remote components, the proxy/stub is responsible for data exchange. Let's talk about the specific change and operation of proxy/stub ......
　　Support MFCUnless for a special reason, we should write the Atl program. It is best not to select this option. You may say that, without the support of MFC, what should you do with cstring? Let me tell you a secret. I don't tell anyone, so I will live with this secret for the rest of my life:
1. Do you know STL? It can be replaced by string in STL;
2. Write a mystring class by yourself;
3. quietly and secretly, do not tell others (especially don't tell Microsoft), and use the cstring source code in MFC;
4. Using the ccombstr class can at least simplify string operations;
5. directly use APIs to operate strings. When we all learn the C language, we start from here. (Not to mention, huh, huh)
　　Support MTSSupports transaction processing, that is, whether the COM + function is supported. COM + may be introduced back in 99th.

Iii. Add ATL object classes

Step 3.1: Choose Insert/new ATL object... (or right-click to pop up the menu in the classview card), select the object category, and select the simple object project. See figure 2.

Figure 2. Select to create a simple COM Object

　　CATEGORY objectCommon components. There are many types of component objects that can be selected, but in essence, it is to let the wizard add some interfaces for us by default. For example, if we select "Simple Object", the wizard adds the iunknown interface to our components; if we select "Internet Explorer Object", the wizard adds the iunknown interface, add an iobjectwithsite interface for IE. Of course, we can add any interfaces manually.
　　CATEGORY controlsActiveX control. You can select many ActiveX types. We will discuss ActiveX programming later.
　　CATEGORY MiscellaneousAuxiliary miscellaneous components.
　　Categroy Data AccessDatabase components (I hate database programming, so I won't ).

Step 3.2: Add a custom cfun (interface ifun), as shown in figure 3.

Figure 3. Names of input classes
In fact, we only need to enter the short name (short name), and other projects will be automatically filled in. There is nothing to say, just pay attention to the progid item. The default progid construction method is "project name. Short name ".

Step 3.3: Fill in interface properties, as shown in figure 4.

Figure 4 interface attributes

　　Threading modelSelect the thread model supported by the component. Com thread, I think it is the most annoying and complex part. The concept of COM thread and apartment will be provided for further introduction. Now all of us choose apartment. What does it mean? Simply put, when a component function is called in a thread, these calls are queued. Therefore, in this mode, we do not need to consider synchronization for the moment. (Note 1)
　　 InterfaceInterface basic type. Dual indicates that dual interfaces are supported (note 2). This is very important and very common, but we will not talk about it today. Custom indicates a custom excuse.Remember! Remember! In our first com program, you must select it !!!!(If you have selected an error, delete all the content and try again .)
Aggregation: whether the components we write can be aggregated by others (note 3) in the future. Only indicates that it must be aggregated before it can be used. It is similar to the pure virtual class in C ++. If you are a chief engineer, you can select it only for designing but not writing code yourself.
　　Support isupporterrorinfoWhether error handling interfaces with rich information are supported. I will talk about it later.
　　Support connection pointsWhether the connection point interface (event and callback) is supported ). I will talk about it later.
　　Free threaded already ALERI won't talk about it in the future. I won't talk about killing you! (Note 4)

4. Add interface functions


Figure 5. Call up the menu for adding an Interface Method

Figure 6. Add an interface function

Figure 7. Add an interface function cat

Add the add () function strictly in the way shown in Figure 6. Since the parameter of the CAT () function added in Figure 7 is relatively long, I do not have proper spaces, please note when entering the information yourself. [In] indicates that the parameter direction is input; [out] indicates that the parameter direction is output; [out, retval] indicates that the parameter direction is output and can be used as the return value of the function operation result. A function can have multiple [in] and [out], but [retval] can only have one, and it must be combined with [out] and placed in the last position. (Note 5)

Figure 8. Illustration after interface function definition
We all know that to change class functions in C ++, we need to modify two places: header file (. h) class function declaration. The second is the function body (. CPP) file implementation. Now, if we use ATL to write component programs, we need to modify the interface definition (IDL) file. Don't worry, IDL will discuss it next time.
Due to the bug in vc6.0, after adding interfaces and interface functions, you may not see the style shown in figure 8. Solution:
　

1	Close the project and open it again	This method is often valid
2	Close the IDE and run it again
3	Open the IDL file and check whether the interface function is correct. If not, modify it.
4	Open the IDL file, modify it (add a space and then delete the space), and save	This method is often valid
5	Open the H/CPP file and check whether the function exists or is correct. If yes, modify it.	Wu zejiayi, do not talk about this idiom.
6	Delete the interface functions in IDL/h/CPP, and then	Try again
7	Re-build the project, re-install VC, re-install windows, smash the computer	Click it!

5. Implement interface functions

The cfun/ifun/Add (...) in double-click graph 8 can start to input the function implementation:

STDMETHODIMP CFun::Add(long n1, long n2, long *pVal){*pVal = n1 + n2;return S_OK;}

This is too simple, and it is no longer a waste of words ". Below we implement the CAT () function for string connection:

Stdmethodimp cfun: CAT (BSTR S1, BSTR S2, BSTR * pval) {int nlen1 =: sysstringlen (S1); // The length of S1 is int nlen2 = :: sysstringlen (S2); // S2 character length * pval =: sysallocstringlen (S1, nlen1 + nlen2 ); // construct a new BSTR and save S1 to If (nlen2) {: memcpy (* pval + nlen1, S2, nlen2 * sizeof (wchar )); // then connect S2 to/wcscat (* pval, S2);} return s_ OK ;}

Student: The above function implementation is completed by calling the basic API.
Teacher: Yes. To be honest, it's really tricky.
Student: We use memcpy () to connect the second string. Why not use the wcscat () function?
INSTRUCTOR: it is acceptable in most cases, but you need to know that BSTR contains a string length, so the actual BSTR string content can store l''/0, however, the wcscat () function uses l''/0'' as the end mark of replication, and data may be lost. Do you understand?
Student: understand, understand. After reading "Data Type of COM Component Design and Application (3)", I will understand it. Is there any simple way, teacher?
Teacher: Yes, you see ......

STDMETHODIMP CFun::Cat(BSTR s1, BSTR s2, BSTR *pVal){CComBSTR sResult( s1 );sResult.AppendBSTR( s2 );*pVal = sResult.Copy();//*pVal = sResult.Detach();return S_OK;}

Student: Haha, good! Using ccombstr is much simpler. What is the difference between ccombstr: Copy () and ccombstr: Detach?
INSTRUCTOR: ccombstr: Copy () will make a copy of BSTR. In addition, ccombstr: copyto () has similar functions. Ccombstr: Detach () is to strip the object from the internal BSTR pointer. This function is a little faster because there is no replication process. However, you must note that this object cannot be used once it is stripped.
Student: teacher, you are talking too well. I admire you for your respect, such as the mountains and mountains ......
Instructor: Stop, stop! Leave homework ......
1. Write this component according to the content described today;
2. Whether you understand it or not, observe the IDL file and CPP file;
3. What files are generated after compilation? If it is a text file, open it;
4. Download the sample program (vc6.0) in this article to compile and run it. Then, preview the call methods in the sample program;
Student: You know, class is coming soon. I want to go to the bathroom. I can't hold it down ......
INSTRUCTOR: class! Don't forget to post my post ......

Vi. Summary

This section describes how to create the first ATL component program and how to use this component. Please pay attention to "COM Component Design and Application (7)".
　

NOTE 1: The Apartment system queues component calls through hidden window messages, so we can temporarily ignore the synchronization issue. Note: It is temporary.
Note 2: The dual interface indicates that both the custom interface and the idispatch interface are supported in an interface. Later, later. Because dual interfaces are very important, we will talk about them every day, night, and often ------ "Three Stresses" for short ":)
NOTE 3: There are two reuse methods for components, aggregation and inclusion.
NOTE 4: The name function is nice, but Microsoft does not.
Note 5: these are concepts in the IDL file. We will introduce what will be used in the future.