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Setting the off-line mode
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| Total Hit (3802) |
You can programmatically set the Internet Explorer off-line mode with the InternetSetOption API, as this code snippet demonstrates:
«Code LangId=1»
Const INTERNET_OPTION_CONNECTED_STATE = 50
Const INTERNET_STATE_CONNECTED = 1
Const INTERNET_STATE_DISCONNECTED = 2
Const INTERNET_STATE_DISCONNE
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Never use the GetLastError API function
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| Total Hit (3710) |
If you heavily use API calls and strictly follow the SDK documentation, you might be tempted to use the GetLastError API to retrieve the error returned by your last API function or procedure. However, this function doesn't always return valid error codes, because Visual Basic internally does a lot o
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Use Currency instead of LARGE_INTEGER values
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| Total Hit (3315) |
A few API calls require that you pass one or more LARGE_INTEGER arguments. These are 64-bit integer values, defined as follows:
«Code LangId=1»
Type LARGE_INTEGER
lowpart As Long ' lower 32-bit value
highpart As Long ' higher 32-bit value
End Type
«/Code»
Unfortunately, wor
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Reduce activation delays by sorting DCOM protocol list properly
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| Total Hit (1884) |
When the client and the server machine have different communication protocol lists you can experience serious delays when the client tries to instantiate an object on the server, and you can even get an error if the two protocol lists don't have any protocol in common.
For best response times, us
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Avoiding Access Denied erros when raising events from MTS objects
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| Total Hit (3071) |
If you don't take specific actions, you get an Access Denied Error when you try to raise an event from an MTS component into a client. This happens because the client executable doesn't have the proper DCOM security settings to let the server call it back. In order to have it working you have two so
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Be careful in using CreateObject with two arguments
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| Total Hit (2998) |
If you install a COM+ application proxy on a client and open its Properties dialog, you'll see that the field "Remote Server Name" is set to the server where you created and exported the application. Before you export the component, you can also change the server name by setting the "Application Pro
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Disable COM+ 1.5 applications and components
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| Total Hit (2830) |
COM+ 1.5 (provided with Windows XP) has an interesting feature that is missing in COM+ 1.0: the ability to disable entire COM+ applications or just their individual components. You can disable and re-enable a COM+ application or component by right-clicking on it in the Component Services MMC explore
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Don't let binary compatibility beat you
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| Total Hit (2754) |
When you decide to release a new version of an MTS/COM+ component you should take care of its compatibility with the previous version. There are three types of changes you could make:
(1) You change only internal code of a component, keeping the interface that the component provides untouched.
(
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Don't store object variables in the SPM
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| Total Hit (2598) |
Some MTS/COM+ newbies wonder whether it is legal to store object variables in the SPM.
No, you can't!! the SPM is unaware of Apartment marshaling issues. If you ask the SPM for an interface pointer while running in an apartment that is different from the one where the interface pointer resides t
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Don't use global variables in MTS/COM+ projects
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| Total Hit (2627) |
Public variables at module level are thread specific. Each new thread starts get a new fresh & uninitialized copy of such variables. All the activities that are born from the same object context always run in the same apartment (You can confirm this by checking the thread ID) as if the object contex
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Generating IDL code to overcome binary compatibility issues
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| Total Hit (3488) |
Among the different COM details that VB hides to the programmers, one of the most problematic one is that it doesn't let you take control on interface GUIDs. Binary compatibility settings in VB try to make you follow COM rules (as a fact breaking such rules with the interface forward mechanism it si
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GetObjectContext.CreateInstance is obsolete in COM+
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| Total Hit (3538) |
CreateInstance was necessary in COM to provide a COM object activation mechanism that could be hooked by the MTS runtime before the activation request reached the COM runtime. So that MTS could apply some pre and post activation magic to put a wrapper around the real object and return this wrapper t
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Improve availability by running a COM+ app as an NT service
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| Total Hit (1747) |
COM+ 1.5 has the ability to run any server application as a NT service, so that the application is up and running when the machine reboots, before any client makes the first requests. This improves the response time of the COM+ application. Besides, running a COM+ app as a service means that it can
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Correctly restore mouse cursor
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| Total Hit (3317) |
When you write lengthy procedures, it is a good habit to change the mouse cursor to an hourglass, and restore it to the original shape when the procedure exits. However, this cursor tracking may be rather difficult when the procedure has multiple exit points, or when it can exit abruptly because of
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Determine the number of mouse buttons
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| Total Hit (3117) |
Sometimes is useful to know how many buttons the user's mouse has. This value can be obtained by calling GetSystemMetrics. The constant to pass as parameter is SM_ CMOUSEBUTTONS. Here's an example:
«Code LangId=1»
Const SM_CMOUSEBUTTONS = 43
Private Declare Function GetSystemMetrics Lib "user3
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Hide and show the mouse cursor
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| Total Hit (3105) |
At times you may want to temporarily hide the mouse cursor, for example in order to reduce flickering. To do so you just need the ShowCursor API function:
«Code LangId=1»
Private Declare Function ShowCursor Lib "user32" (ByVal bShow As Long) As Long
' hide the mouse
ShowCursor False
' do
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Intercepting MouseEnter and MouseExit events without subclassing
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| Total Hit (3912) |
Visual Basic raises the MouseMove event when the mouse cursor is within a control, so it's easy to know when the cursor "enters" a control. However, determining when the mouse leaves the control is more difficult.
You can solve this problem by monitoring the first time the control raises the Mous
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Swap the mouse buttons' behavior and meaning
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| Total Hit (4057) |
You can programmatically swap the meaning of the left and right mouse buttons, to account for your left-handed users. All you need is a call to the SystemParameterInfo API function
«Code LangId=1»
Private Declare Function SystemParametersInfo Lib "user32" Alias _
"SystemParametersInfoA" (By
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The status of mouse buttons
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| Total Hit (3308) |
Visual Basic lets you test the state of mouse buttons only inside a MouseDown, MouseMove, or MouseUp event procedure. To determine the current state of mouse buttons you can use one of the following functions:
«Code LangId=1»
Private Declare Function GetAsyncKeyState Lib "user32" (ByVal vKey As
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The status of shift keys
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| Total Hit (2870) |
Visual Basic lets you test the state of the Shift, Alt and Ctrl keys only within the KeyUp, KeyDown and all the mouse-related event procedures. If you want to test the state of these keys from within another routine, you can resort to the following functions:
«Code LangId=1»
Private Declare Fun
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Check for a valid URL
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| Total Hit (3935) |
Before posting an Internet request you should check that the user has entered a valid Internet address. You can do this with a parsing routine, or use the following routine based on the IE5 library:
«Code LangId=1»
Private Declare Function IsValidURL Lib "urlmon" (ByVal pBC As Long, _
url A
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Check whether RAS is installed
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| Total Hit (3114) |
When you work with RAS APIs, you should have to make sure if RAS library is installed on the system. A simple way is to verify the existence of the Rasapi32.dll file in the windows system directory; the same thing can be obtained with a call to the InternetGetConnectedState API, as the following cod
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Check whether the user is working off-line
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| Total Hit (3375) |
Internet Explorer offers the possibility to simulate an Internet connection with the off-line mode. If you want to know if off-line mode is on or off you can use InternetQueryOption API.
«Code LangId=1»
Const INTERNET_OPTION_CONNECTED_STATE = 50
Const INTERNET_STATE_DISCONNECTED_BY_USER = &H10
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Create an Internet shortcut
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| Total Hit (2756) |
Unlike regular LNK shortcut, which contain data in binary file, Internet shortcut files are just text files in this format:
[InternetShortcut]
URL=www.domain.com
Thus it is simple to programmatically create an Internet shortcut that, when double-clicked, will load the default browser and hav
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Download a file with one API call
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| Total Hit (3637) |
If you have Internet Explorer 5 or later version, you can use an API call to download a file from the Internet withouth displaying any message box.
«Code LangId=1»
Private Declare Function URLDownloadToFile Lib "urlmon" Alias _
"URLDownloadToFileA" (ByVal pCaller As Long, ByVal szURL As Strin
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Get the local IP address using the Internet Transfer Control
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| Total Hit (2519) |
The easiest way to retrieve the IP address assigned to the local machine during an Internet session is by means of the LocalIP property of the Internet Transfer Control:
«Code LangId=1»
MsgBox "IP address= " & Winsock1.LocalIp
«/Code»
Note that getting the same information through API calls
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Launch the default browser on a given URL
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| Total Hit (3945) |
The following routine launches the default browser and loads the specified URL in it. The argument doesn't have to include the HTTP:// prefix. If the operation is successful it returns True.
«Code LangId=1»
Private Declare Function ShellExecute Lib "shell32.dll" Alias "ShellExecuteA" _
(B
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Open the default program for sending email messages
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| Total Hit (2543) |
The ShellExecute API function recognizes email addresses if they are prefixed by the "mailto:" prefix, and correctly run the default program for sending email messages (e.g. Outlook). This lets you open a window for sending an email and automatically fill the address field. Here's a wrapper routine
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Open the Internet Connection dialog
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| Total Hit (3704) |
The dialog you see when you start an Internet connection is implemented in the RNAUI.DLL file, and the specific function is called RnaDial. To open this dialog from your application you can call this function through the rundll32.exe application (located in Windows directory) specifying the name of
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Put buffering and Response.Flush to good use
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| Total Hit (2373) |
IIS5 enables buffering by default, therefore all the output from your ASP is actually sent to the browser only when the page completes its processing. In many cases this approach improves the overall processing speed, and indirectly makes for a more scalable site. However, buffering has two minor de
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