gabehabe » c++

wxWidgets: Loading Symbols from a DLL (and using ::Connect)

Danny — Fri, 09 Apr 2010 20:20:08 +0000

[Apologies if the entry is a little unclear, I just threw this together in about 10 minutes, I wanna get it out there... it's fucking hard to find any sort of information when it comes to this at the moment]

Quick entry, gonna turn this into a tutorial soon. The code is a bit of a mess, since I was just throwing stuff together while I was figuring this out. I’ll tidy it up when it’s tutorial tiems.

Basically, I recently developed a [url=http://snip.gd/plugins.php]plugin system[/url] for my [url=http://snip.gd/]snippet manager[/url]. The way it works is simple: It loads symbols from a DLL into the application, which can be called from a dynamically created menu. First off, the main code [this is the messy bit for the time being]

This code opens a subdirectory within the working directory called “plugins”, and grabs all the DLLs from them. If the DLL contains a symbol called SnippetManagerPluginMain (the only required symbol for the plugins, I kept them simple) it will add it to the menu.

Additionally, it also checks for two optional optional symbols, which are pretty cool. They simply return strings, which assign the name and the keyboard shortcut for the plugin. If neither is set, it has no keyboard shortcut, and the name defaults to the name of the DLL file.

    ///  
    #if defined(__WXMSW__) // windows plugins - load ./plugins/*.dll
    if(wxDir::Exists(wxT("./plugins/"))) {
        wxDir plugin_dir(wxT("./plugins/"));
        if(plugin_dir.HasFiles()) {
            wxArrayString files;
            wxDir::GetAllFiles(wxT("./plugins/"), &files);
            wxMenu* plugin_menu = new wxMenu(wxT(""));
            wxDynamicLibrary* lib;
            wxString label;
            char* ks;
            bool showmenu = false;
            for(unsigned int i = 0; i < files.GetCount(); i++) {
                lib = new wxDynamicLibrary();
                if(files.Item(i).Find(wxT(".dll")) != -1) {
                    lib->Load(files[i]);
                    if(lib->HasSymbol(L"SnippetManagerPluginMain")) {
                        showmenu = true;
                        if(lib->HasSymbol(L"SnippetManagerPluginName")) {
                            label = wxString(((SnippetManagerPluginName)lib->GetSymbol(L"SnippetManagerPluginName"))(), wxConvUTF8);
                        } else {
                            label = files[i].AfterFirst('\\').AfterFirst('\\').BeforeLast('.');
                        }
                        this->plugins.push_back((SnippetManagerPlugin)lib->GetSymbol(L"SnippetManagerPluginMain"));
 
                        if(lib->HasSymbol(L"SnippetManagerKeyboardShortcut")) {
                            ks = ((SnippetManagerKeyboardShortcut)lib->GetSymbol(L"SnippetManagerKeyboardShortcut"))();
                            label += L"\t" + wxString(ks, wxConvUTF8);
 
                        }
                        plugin_menu->Append(wxID_PLUGIN + i, label);
                        Connect(wxID_PLUGIN + i, wxEVT_COMMAND_MENU_SELECTED, wxCommandEventHandler(Snippet_ManagerFrame::handle_plugin));
                    }
                }
            }
            if(showmenu) {
                mbar->Append(plugin_menu, wxT("&Plugins"));
            }
        }
    }
    #endif
    /// [

In order to bind the events to the menu, the ::Connect method is called. This is an alternative to using EVENT_TABLE, and allows events to be allocated dynamically at runtime. wxID_PLUGIN is a custom variable, and basically, any of the menu items within the menu will call the main frame’s [il]handle_plugin[/il] method. The important part, however, is the fact that each one has a different ID, even though they use the same method.

The method itself then uses the ID of the event calling it to lookup the DLL’s symbol, which were added in this->plugins.

void Snippet_ManagerFrame::handle_plugin(wxCommandEvent &e) {
    this->plugins[e.GetId() - wxID_PLUGIN](this->ui->uid.mb_str(), fill_p_snip(this->ui->get_active_stc()->snip, this->ui->get_active_stc()->GetText()));
}

Of course, some of the code here doesn’t really mean jack all, since there are custom methods and stuff used in it. But the base of it is clear. I’ll try to write another (small) application and a tutorial covering the steps over the weekend.

Until then, have fun! :)

wxWidgets: Threading, and using the Clipboard

Danny — Sat, 31 Oct 2009 17:11:12 +0000

wxWidgets: Threading, and using the Clipboard

Two for one in this tutorial. We're going to create a thread using wxWidgets, and make it monitor the clipboard for text. Then, if we detect a change, we're going to add the new contents to a list. It's a relatively simple process, but unfortunately wxWidgets isn't the most documented GUI toolkit out there. So, let's get started. I'm gonna pile all the code into a single file instead of breaking my classes up into seperate files, just for ease of navigation in this tutorial. The code is relatively short anyway, with only 62 lines. First off, as with any other program, we're going to want to get our includes done. We'll be needing three: The standard wx header, the clipboard header, and the thread header.

#include  // standard wx header
#include  // clipboard - we'll monitor the clipboard for text
#include  // include threads!

The next thing we need to do is declare our ClipLogger class - this will inherit wxThread, and have two variables: One to hold the most recent text that we got from the clipboard, and one which is a pointer to a wxListBox object -- the object on the main window which we'll be updating.

class ClipLogger : public wxThread {
    public:
        ClipLogger(wxListBox*);
    private:
        void* Entry(); // the entry point to the thread
 
        wxString LatestText; // store the last text so we can check for changes
        wxListBox* list; // the list to update on a text change
};

The constructor is very simple. All it does is take a wxListBox*, and assign it to a variable stored by the class - this is the list that we want to update on clipboard text changes.

ClipLogger::ClipLogger(wxListBox* l) {
    this->list = l;
}

Next up is the main part of this tutorial. When we create a thread, we need to override the Entry() method of the class, like so:

void* ClipLogger::Entry() {

To save time and memory, rather than creating a variable every time we loop, we'll create it before and simply overwrite it inside the loop.

wxTextDataObject temp;

wxTextDataObject is the type of object that the clipboard will store. Next, since our thread is a constant "monitor" for the clipboard, we want it to loop.

while (true) {

Then, we need to think about how we can help our application not be CPU-hungry. The simple solution is to make the thread sleep each time it loops. We can do this with wxSleep(int time), where time is the length of time to sleep in seconds.

wxSleep(1);

The rest of the loop is the clipboard. It's very simple, so rather than break it up line-by-line, I've added comments along the way. We basically need to do the following: - Open the clipboard - If the clipboard is text, get it into our temp variable - Update the list and remember this is the most recent (so as not to constantly add the same data to the list) - Close the clipboard

        if (wxTheClipboard->Open()) { // try to open the clipboard
            if (wxTheClipboard->IsSupported(wxDF_TEXT)) { // if the clipboard contains text
                wxTheClipboard->GetData(temp); // get the data from the clipboard
                if (this->LatestText != temp.GetText()) { // if it's changed, we want to update
                    if (temp.GetText() != wxT("")) { // if it's not an empty string
                        this->LatestText = temp.GetText();  // update the "LatestText"
                        this->list->Append(temp.GetText()); // append to the list
                    }
                }
            }
        }
        wxTheClipboard->Close(); // close the clipboard

The last thing left to do in the thread is simply close it off, and close off the loop.

}
}

Simple, huh? :) And that's our thread defined. Now all we need to do is create the app itself, which is a simple process. I hope that you already know how to do it, so we can blitz through the majority of it. Create the app:

class threaded_app : public wxApp {
    public:
        bool OnInit(void);
};

The beginning of the OnInit() should be nothing new at this point either.

bool threaded_app::OnInit(void) {
    // quickly create a wxFrame to display a window
    wxFrame* f = new wxFrame(NULL, wxID_ANY, wxT("Threaded App!"));
 
    // add a list to the frame we created
    wxListBox* list = new wxListBox(f, wxID_ANY);
 
    // display the frame
    f->Show(true);

The last part of OnInit() that we need to do is actually create an instance of our thread and run it, like so:

    // pass the list to the clipboard monitor so it knows what to update
    ClipLogger* cl = new ClipLogger(list); // construct our thread
    cl->Create(); // we have to create a thread before we can run it
    cl->Run(); // run our thread

And we can simply finish off the OnInit() and IMPLEMENT_APP:

    return true;
}
 
IMPLEMENT_APP(threaded_app)

And that's all there is to threading and using the clipboard in wxWidgets! Here's the complete code:

#include  // standard wx header
#include  // clipboard - we'll monitor the clipboard for text
#include  // include threads!
 
class ClipLogger : public wxThread {
    public:
        ClipLogger(wxListBox*);
    private:
        void* Entry(); // the entry point to the thread
 
        wxString LatestText; // store the last text so we can check for changes
        wxListBox* list; // the list to update on a text change
};
 
ClipLogger::ClipLogger(wxListBox* l) {
    this->list = l;
}
 
void* ClipLogger::Entry() {
    wxTextDataObject temp; // create a "wxTextDataObject" to get the info from the clipboard
    while (true) { // our thread will loop
        wxSleep(1); // sleep for 1 second, make the thread less cpu-hungry
        if (wxTheClipboard->Open()) { // try to open the clipboard
            if (wxTheClipboard->IsSupported(wxDF_TEXT)) { // if the clipboard contains text
                wxTheClipboard->GetData(temp); // get the data from the clipboard
                if (this->LatestText != temp.GetText()) { // if it's changed, we want to update
                    if (temp.GetText() != wxT("")) { // if it's not an empty string
                        this->LatestText = temp.GetText();  // update the "LatestText"
                        this->list->Append(temp.GetText()); // append to the list
                    }
                }
            }
        }
        wxTheClipboard->Close(); // close the clipboard
    }
}
 
class threaded_app : public wxApp {
    public:
        bool OnInit(void);
};
 
bool threaded_app::OnInit(void) {
    // quickly create a wxFrame to display a window
    wxFrame* f = new wxFrame(NULL, wxID_ANY, wxT("Threaded App!"));
 
    // add a list to the frame we created
    wxListBox* list = new wxListBox(f, wxID_ANY);
 
    // display the frame
    f->Show(true);
 
    // pass the list to the clipboard monitor so it knows what to update
    ClipLogger* cl = new ClipLogger(list); // construct our thread
    cl->Create(); // we have to create a thread before we can run it
    cl->Run(); // run our thread
 
    return true;
}
 
IMPLEMENT_APP(threaded_app)

Happy coding! :)

wxWidgets: Keyboard Shortcuts without a Menu

Danny — Thu, 10 Sep 2009 22:25:08 +0000

Quick entry. Sort of a preview. I’m working on a tutorial for dream.in.code about creating keyboard shortcuts in a wxWidgets application (particularly using C++), and figured I’d share the code here, too.

(After I’ve finally gotten around to installing this syntax highlighting plugin for WordPress)

Aaaaannddd… Done!

Right. Back onto the original topic. Damn sidetracked mind. So, when I write a tutorial, I write a whole chunk of code first, and then add the tutorial content around it. Here’s the code for allocating keyboard shortcuts to do different stuff in wxWidgets without using menu items.

// basic setup code, I'll fly past this. If you're not familiar, check out this tutorial:
// http://www.dreamincode.net/forums/showtopic66948.htm
 
#include 
 
class app : public wxApp {
    public:
        virtual bool OnInit();
    private:
        wxTextCtrl* txt;
        wxCheckBox* chk;
 
        void key_shortcut(wxKeyEvent&);
        DECLARE_EVENT_TABLE()
};
 
// if you're not familiar with events, check out this tutorial:
// http://www.dreamincode.net/forums/showtopic67058.htm
 
BEGIN_EVENT_TABLE(app, wxApp)
    EVT_KEY_DOWN(app::key_shortcut)
END_EVENT_TABLE()
 
bool app::OnInit() {
    wxFrame* win = new wxFrame(NULL, wxID_ANY, wxT("Keyboard Shortcuts, No Menu!"), wxDefaultPosition, wxSize(250, 125));
    win->Show(true);
 
    this->txt = new wxTextCtrl(win, wxID_ANY, wxT("Press Ctrl+G to append text to me"), wxPoint(0,0), wxSize(250, 50), wxTE_MULTILINE);
    this->chk = new wxCheckBox(win, wxID_ANY, wxT("Press Ctrl+Left to toggle me."), wxPoint(0, 55), wxDefaultSize);
 
    return true;
}
 
// this is the method I'll be focusing on. The key_shortcut event which we create
// to do fancy stuff without adding billions of menu items
 
void app::key_shortcut(wxKeyEvent& e) {
    // of course, it doesn't have to be the control key. You can use others:
    // http://docs.wxwidgets.org/stable/wx_wxkeyevent.html
    if(e.GetModifiers() == wxMOD_CONTROL) {
        switch(e.GetKeyCode()) {
            case 'G': // can return the upper ASCII value of a key
                // do whatever you like for a Ctrl+G event here!
                this->txt->AppendText(wxT(" gabehabe ftw!"));
                break;
            case WXK_LEFT: // we also have special keycodes for non-ascii values.
                // get a full list of special keycodes here:
                // http://docs.wxwidgets.org/stable/wx_keycodes.html
                this->chk->SetValue(!this->chk->GetValue());
                break;
            default: // do nothing
                break;
        }
    }
}
 
IMPLEMENT_APP(app)

Link to follow when the tutorial is completed and approved.

As promised, here’s the tutorial in all it’s glory:
wxWidgets keyboard shortcuts with no menu