如何在Visual C ++中的单击事件处理程序中发送2个以上的参数（delegate => thing isnt working）

Question

this is what im doing right now !!!

//picture box
pct->Click += gcnew EventHandler(this,&fornow::Form1::Display);

private: System::Void Display(System::Object^ sender, System::EventArgs^ e){
    PictureBox^ pb = safe_cast<PictureBox^>(sender);
    pictureBox1->Image = pb->Image;
}

Apparently I cannot use delegates in C++/Cli im pretty new to this kind of coding !! So could anyone tell me how to send some more arguments to the eventhandler method after clicking so i can use it in the code there !!!

Like I have a System::String , if I could send it like this may be i could write

private: System::Void Display(System::Object^ sender, System::EventArgs^ e, System::String^  s){
    Mat img = imread(s);
    imshow("",img);  
    waitKey(0);
}

im compiling it with /clr and im using trial version vs 2010 Visual C++ .

this code resides in a buttonclick event handler... ive added that part of the code ...

private: System::Void button1_Click(System::Object^ sender, System::EventArgs^ e) {
    // array<System::String^>^ files = 
    //     System::IO::Directory::GetFiles(textBox1->Text,"*.*",
    //     System::IO::SearchOption::AllDirectories);


    pin_ptr<const wchar_t> wch = PtrToStringChars(textBox1->Text);
    wchar_t wch1[260];
    wcscpy(wch1,wch);
    list<basic_string<wchar_t>> dir;
    list<string> s;
    retrieve *r = new retrieve();


    dir = r->print(wch1,dir);

    for(list<basic_string<wchar_t>>::iterator itr = dir.begin(); itr != dir.end();itr++)
    {
        cout<<std::string(itr->begin(),itr->end())<<endl;
        s.push_back(std::string(itr->begin(),itr->end()));
    }

    filter *f = new filter();  
    s=f->filter1(s); // fills s with paths (strings)
    flowLayoutPanel1->Controls->Clear();

    for(list<string>::iterator i=s.begin();i!=s.end();i++)
    {
        std::string sn = std::string(i->begin(),i->end());
        System::String^ s = gcnew System::String(sn.c_str());

        PictureBox^ pct = gcnew PictureBox();
        if(checkBox1->Checked==true)
            pct->Image = Image::FromFile(s)->GetThumbnailImage(50,50,nullptr,System::IntPtr::Zero);
        if(checkBox1->Checked==false)
            pct->Image = Image::FromFile(s);

        pct->Size = System::Drawing::Size(100,100);
        flowLayoutPanel1->Controls->Add(pct);
        pct->Click += gcnew EventHandler(this,&fornow::Form1::Display);
        Mat img = imread(sn);
        imshow(sn,img);
        waitKey(0);
    }

Im sorry im really new to this kind of coding .. any suggestions will be helpful thanks !!!

Answer 1

You can't add additional parameters to the click event. If you could, where would you expect the UI to get the string from?

Given your comments on lambdas, I think what you're looking for is to have an event handler that is slightly different depending on which picture was clicked. Is that correct? Something like this in C#:

// If you were writing C#, is this what you'd do?
pct1.Click += (s,e) => imshow(imread("one.jpg"));
pct2.Click += (s,e) => imshow(imread("two.jpg"));

There's no strict equivalent to that in C++/CLI. However, if you think about what the lambdas are doing, you can do that in C++/CLI. The lambdas are turned into regular methods on the same class, and you can do that in C++/CLI.

pct1->Click += gcnew EventHandler(this,&fornow::Form1::Display1);
pct2->Click += gcnew EventHandler(this,&fornow::Form1::Display2);

void Display1(Object^ sender, EventArgs^ e)
{
    Display(safe_cast<PictureBox^>(sender), "one.jpg");
}

void Display2(Object^ sender, EventArgs^ e)
{
    Display(safe_cast<PictureBox^>(sender), "two.jpg");
}

void Display(PictureBox^ pb, String^ file)
    Mat img = imread(file);
    imshow(pb, img);  
    waitKey(0);
}

Alternatively, you could have a single event handler, which looked at which picture was clicked (the sender) to do its work.

pct1->Click += gcnew EventHandler(this,&fornow::Form1::Display);
pct2->Click += gcnew EventHandler(this,&fornow::Form1::Display);

void Display(Object^ sender, EventArgs^ e)
{
    PictureBox^ pb = safe_cast<PictureBox^>(sender)
    String^ file;

    if(pb == this->pct1) file = "one.jpg";
    else if(pb == this->pct2) file = "two.jpg";
    else return;

    Mat img = imread(file);
    imshow(pb, img);  
    waitKey(0);
}

Answer 2

Pack the parameters into a ref class derived from EventArgs, then you can use the generic version of EventHandler like this

public ref class MyEventArgs:EventArgs
{
public:
    property String^ Parameter1;
}

public ref class MyClass
{
public:
    event EventHandler<MyEventArgs^> ^ MyEvent;
    void RaiseMyEvent(Object^ sender, String^ parameter1)
    {           
        MyEventArgs^ args=gcnew MyEventArgs();
        args->Parameter1=parameter1;
        MyEvent(sender, args);
    }
};

Your event handler methods would have the signature

void MyEventHandler(Object^ sender, MyEventArgs^ args)

and have access to the values passed to RaiseMyEvent via the properties of the args parameter.