Video: How Do I: Determine if a Combo Box Drop-Down List is Visible within the .NET Compact Framework?

Presenter:Jim Wilson

In this video, Jim Wilson demonstrates how to find out whether a combo box drop-down list is currently visible using Windows messages. This allows you to work around the absence of support for the ComboBox.DroppedDown property in the .NET Compact Framework.
The following text is a software generated transcript of the video. Click on a minute link to jump to a location within the video


Minute 0
Jaime Mr Wilson President didn t have incorporate in this video just thought about how you can determine whether a combo boxes from now is currently visible or not the issue is that in the full net framework become a box that has a property called drops down and it tells you whether the drop down is currently before I return truths visible false it s not in the context for what we ll nicely have access to this property does not support it is a weenie to do is find some other way to determine if this were not obviously I found to do this to take advantage of Windows messages do the same thing with a look here was indecisive masses don t see me get dropped state with a look of that was it that saves the Win32 message that of a writing accuracy Win32 code and what actually we actually used to go out and get that information

Minute 1
So you see to get off the messages is actually very simple for all you really need to do is is called a sent message to the handle of the control your should in than the message itself and no other information and basically it will return back to you a one if it is visible in his year of drought that is not visible to receive antifreeze and put together Cisco accurate Visual Studio to start a project so great as her go well with those windows mobile six Pocket PC project is a huge arm or toys with most of professional program for desires to drive her VS projects and initiatives will call this the demo yet dropped the case we have that sister and great project will see that brings together of his very simple

Minute 2
If you were to Win32 messages in the past few mercy are supposed with coder others simply be very familiar to you if you haven t defined although Denise has been given for is so very he s worked with current sales the first we want to do is go out for form and released it a combo box on their release test how things work is an artform number of a toolbox which took a little things your refrigerator do as the combo box on the form again and large settlement and for simplest clickable of values he urges would induce a basic things say low to buy law and audience and it s been like a notice of a few strings in their nose into a text box on here that will use the display with the current status is into that of their as it now what I want to do is alright a little program so that we can test the drops

Minute 3
Econobox and will display a message in this tight spots indicating whether drop down or not it s pretty reasonable test varmint and so soon is that Cisco rear with a menu of your skull of test and was named a menu itself when you test it with another manual here is for exit ghost Avenue exit in case you got that the menu at Israel uses the student data with say a close is a getting close the form for us and got that so go back to her desire with input in the test had focuses for our function to test to see if dropped out of the echo of struct are sure not

Minute 4
Post something combo box and was told about dropped down surveys in a very similar to the full first property is present in the drop down property signal parameter is a combo box local target as a way to do now is use at Windows message that seen me to get dropped states now he never organisms messaged you know that each Windows message is actually just an integer so we may understand this was the integer value that corresponds the CD greets me CD get dropped state easily do that is us a look at the header files and see our files so it earlier when there were two program files on a machine only to the Windows mobile success to get little success decay and unified PC area into the header files and why one year is a file called Win user h is which runs a gun under win

Minute 5
User h and got that there was a Visual Studio and we take a look here just will find the environment for CB_get dropped states never take a look within and see me get from state has a value of accessible 157 we needed to justify cost of that same guy spin coming to sell your guy without closes window and backyard code justify comes to cars and a face that in which the disorders are visiting on a constant was a constant to find we can go ahead and send a message now if you want to send up in a Windows message remember that the original functions in the SDK are either send message and PostMessage misspeaks a week which is an opinion vote out and call those with turned out that

Minute 6
We examine exist to those from weather com or from her classes in the and the reference here in a reference in what he is is that it would hear Microsoft Windows see enough wars manually careful this is a lot of different forms a cemetery to a Windows CE forums register so it is a forms of much of the one s mold of forms and why should you get Microsoft Windows CE forms is written at that reference together their banana using for as well Windows CE platforms and notice here particular classical message window that is what is the class is often use whatever you have to do some kind of them direct Windows message processing of drone and that s order to hear only why do

Minute 7
A message that you would pick on just did a test and message would just ask is this instance of this message gets away with it and create a message and declared us that message structure will just want to talk to him though Fox message now when you create when this is a message structure you don t use new is that what you do is use the messages static create function in and I crave longshoremen identify all the values his predicament here is the first it wants is the window you would send a message or that s what we are targets or your users handle property access the Windows handle for another message we want to stand as her CV drop state

Minute 8
Pressure to get drop state now for this mess is a wParam and the lParam are both zero thing is that it is a type of those is actually in four enemies he can t just put zeros there gets the number zero with our complaint is your thought about it for what we can do is to say and foreigner 0 so that now pass actions your diet are ends in foreigner 0 and now that constructs a message to the masses of all the information is out there for you to send message it takes to a reference message was a ref message is as weird combo box messes and together go there to know how it is that we will send messes his icy drops down to the Win32 layer

Minute 9
Doesn t actually send messages and eyes and gave it and then the way we find out the results of that send messages the gate or box message and as a result member when I get him for now the way the message were sizing to get our state if it be drop down is visible and returns a one is not visible returns zero within result is an importer right so I can t do is avoid this return call us a message result equals one vacated against the bar complaining is a one is not about importer now I could go off and construct an importer with a value of one programmer that we automatically have access to the values euro rate selector always checking it is importer 0 cable zero means it s not dropped

Minute 10
Oh then it is visible right so basically we discouraged up to the message sent to the window when response so that I respond back with his night was euro that means a drop down is visible that I is euro and instruct us not visible by and that s all we have to do the test is not as that s very simple now we can do here is a definitive statement in a caller function combo box object combo box drop down and core function will pass in our combo box stumble box 1 because the target is a knife that returns true regular text box since text property to be the combo box which does little steer dropped down is visible to other wives will say

Minute 11
Xbox txt equals drop down is not visible to do that and it s announced it would build maternity typos or anything at all bills find so now it has our application will run it will run it basically will put the tasks pursued a message gets here they will try dropping this down for business again is the message is there if everything goes as it should these values its players should be appropriate for the current and combo boxes which was in a debug start debugging them to use the weasels of classic emulator is foreign to deploy it okay to signal to know it got dropped down as the display season out of the drop down as visible as a desolate and in his immediate drop down is visible

Minute 12
If I collapse it comes as blood and get drop down is not visible to have drafted a visit to drop down upon his visible select something I gone it is not visible is their habit basically just by using a Windows message and relaxing to talk directly to the control as we tickled by Turner code this same technique can be used any time you need to information up now when list controls does not expose you for property or one or one of the key cut of motivators behind a common friend is debasing small is not uncommon for them to choose not to carry information just as the one in large size controls is the first example where precipitating a look finding the for Windows message we re able drives as control directly results think in many ways Jim Wilson and present it as a corporate extra time

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