AxAcroPDF swallowing keys, how to get it to stop?

Question

The AxAcroPDF swallows all key-related events as soon as it gets focus, including shortcuts, key presses, etc. I added a message filter, and it doesn't get any key-related messages either. It's a COM component, could that be relevant?

Is there any way to catch these before the control starts swallowing them?

Answer 1

Hans is correct, the Acrobat Reader spawns two child AcroRd32 processes which you have no direct access to from within your managed code.

I have experimented with this and you have three viable options:

1. You can create a global system hook, and then look for and filter out / respond to WM_SETFOCUS messages sent to your child AcroRd32 windows. You can accomplish some of this from within C# by using a wrapper library, such as the one here: http://www.codeproject.com/KB/system/WilsonSystemGlobalHooks.aspx

   You also need to identify the correct processes as there may be more than one instance of your application, or other instances of AcroRd32. This is the most deterministic solution, but because your application will now be filtering messages sent to every single window in existence, I generally don't recommend this approach because then your program could negatively affect system stability.

2. Find an alternate PDF viewing control. See this answer for a few commercial components: .net PDF Viewer control , or roll your own: http://www.codeproject.com/KB/applications/PDFViewerControl.aspx

3. Find an acceptable hack. Depending on how robust your application needs to be, code such as the following may be suitable (it was suitable for my case):

   DateTime _lastRenav = DateTime.MinValue;
   
   public Form1()
   {
       InitializeComponent();
   
       listBox1.LostFocus += new EventHandler(listBox1_LostFocus);
   }
   
   private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
   {
       axAcroPDF1.src = "sample.pdf";  //this will cause adobe to take away the focus
       _lastRenav = DateTime.Now;
   }
   
   void listBox1_LostFocus(object sender, EventArgs e)
   {
       //restores focus if it were the result of a listbox navigation
       if ((DateTime.Now - _lastRenav).TotalSeconds < 1)
           listBox1.Focus();
   }
   

Answer 2

I might finally have a ridiculously simple answer. So far in testing this is working.

Having suffered from this problem for quite some time and having built a complex system of each custom control recording which of them last had focus and using a timer to flip focus back (when acropdf grabbed it) I revisited this problem and read a great number of answers (looking for recent solutions). The information gleaned helped me with the idea.

The idea is to disable the (acropdf) control whilst it is loading as in the following example (code reduced for clarity)

AxAcroPDF_this.Enabled = False AxAcroPDF_this.src = m_src

Then on a timer, after say 1 second.

AxAcroPDF_this.Enabled = False

Basically the idea is to tell Windows not to let users use the acropdf control until allowed, so asking Windows to prevent it from getting focus (because users are not allowed in there).

So far this is holding up, I will edit this if anything changes. If it doesn't work completely for you then maybe the idea points into a useful direction.

Answer 3

It is an out-of-process COM component, that's the problem. Completely in violation of Windows SDK requirements as laid out in SetParent(). Once its window gets the focus, the message loop in the acroread.exe process gets all the messages, your message filter cannot see any messages anymore.

Technically it is fixable by using SetWindowsHookEx() to inject a DLL into the process and monitor messages with WH_GETMESSAGE. But you can't write such a DLL in the C# language.

Major suck, I know. There never seems to be any lack of it with that program.

Answer 4

For some reason Tim's answer, disabling the AxAcroPDF control directly, didn't work in my case. The Leave event on the previously-selected Textbox would never fire, either.

What is working is nesting the AxAcroPDF control inside of a disabled GroupBox. Since the users of my application need to only see the PDF, not interact with it, the GroupBox's Enabled property is set to False in the designer.