Re: Animating a snake (aka Snafu) - Managed C++/CLI Discussion Boards

Cyclone_S27-Mar-11 14:27

27-Mar-11 14:27

Thanks for the helpful suggestions. I got it to move the snake right fine but I need help with some of the coding to get it to move properly in the other directions. I'm curently trying to move the snake downwards but I'm stuck. Thanks.

#include "stdafx.h"
using namespace System;
using namespace System::Drawing;
using namespace System::Windows::Forms;
using namespace System::Collections::Generic; // Required to make lists.

public ref class snake_segment
{
	public:
			Panel^ panel;

			snake_segment( Form ^ form ) // Class Constructor.
			{ 
				panel = gcnew Panel();
				panel->BackColor = Color::Blue;
				panel->Width = 20; panel->Height = 20;
				form->Controls->Add(panel);
			}
};

public ref class Form1 : public Form 
{
	public:
			List<snake_segment^>^ segments; // A list that contains the snake segments.
			int l; // Length of the snake at begining of game.
			int size; // The number of segments in snake/list.
			int last;  // The last segment of in the snake.
			int x, y; // The coordinates of the snake segment(head).
			int x2,y2; // Values that will store the direction the snake will move.
			Timer^ Timer1; // The timer that will move the snake;
			bool game_started;

			Form1() // Class constructor.
			{	
				segments = gcnew List<snake_segment^>();
				Timer1 = gcnew Timer();
				Timer1->Interval = 2000;
				Timer1->Start();
				Timer1->Tick += gcnew System::EventHandler(this, &Form1::timer1_Tick);
				this->KeyDown += gcnew System::Windows::Forms::KeyEventHandler(this, &Form1::Form_KeyDown);
				Make_Snake();
			}
			
			void Make_Snake()
			{
				double clr = 255;
				double dclr = 128 / 2;

				for(int I = 0; I <= 3; I++)
				{
					snake_segment^ s = gcnew snake_segment(this);
					s->panel->BackColor = Color::FromArgb(0,0,clr);
					segments->Add(s);
					clr -= dclr;
				}

				for each (snake_segment^ s in segments)
				{
					l += s->panel->Width + 2;
					s->panel->Left = l;
				}	
			}

			void get_size_of_snake()
			{
				size=0;
				for each (snake_segment^ s in segments)
				{
					size++;	
				}				
			}

			void head_position() // The head position at start of game.
			{
				x = segments[size-1]->panel->Left;
				y = segments[size-1]->panel->Top;
			}

			void move_snake()
			{
				if(x2 ==1){segments[last]->panel->Left = x + segments[last]->panel->Width + 2;} // Move snake right.
				if(y2 == -1){segments[last]->panel->Left = x;segments[last]->panel->Top = x;} // Move snake down.
				x = segments[last]->panel->Left;
				y = segments[last]->panel->Top;
				last++;
				if(last >= size){last=0;}
			}

			System::Void timer1_Tick(System::Object^  sender, System::EventArgs^  e) // A timer that will move the snake;
			{
				get_size_of_snake();
				if(!game_started){head_position();game_started=true;} // Find first head position at start of game.
				move_snake();
			}

			System::Void Form_KeyDown(System::Object^ sender, System::Windows::Forms::KeyEventArgs^ e)
			{
				if(e->KeyCode == Keys::Down){y2 = -1;}
				if(e->KeyCode == Keys::Up){y2 = 1;}
				if(e->KeyCode == Keys::Left){x2 = -1;}
				if(e->KeyCode == Keys::Right){x2 = 1;}
			}
};

[STAThread]
int main()
{
    Application::Run(gcnew Form1());
}

Re: Animating a snake (aka Snafu)

Richard Andrew x6427-Mar-11 15:12

Richard Andrew x64

27-Mar-11 15:12

I think you have the values for y2 reversed in the Key handler.

If you want the snake to move down, you should be incrementing y2, and decrementing it for up.

The difficult we do right away...
...the impossible takes slightly longer.

Re: Animating a snake (aka Snafu)

Cyclone_S27-Mar-11 15:25

Cyclone_S

27-Mar-11 15:25

The snake automaticaly moves once the right key is pressed. It sorta works but not sure on how to code it for it moving downwords.

Here is the move_snake function;

void move_snake()
			{
				if(x2 ==1) // Move snake right.
				{
					segments[last]->panel->Left = x + segments[last]->panel->Width + 2;
					x = segments[last]->panel->Left;
					y = segments[last]->panel->Top;
					last++;
					if(last >= size){last=0;}
				} 
				if(y2 == -1) // Move snake down.
				{
					segments[last]->panel->Top = y + segments[last]->panel->Height + 2;
					segments[last]->panel->Left = x;
					x = segments[last]->panel->Left;
					y = segments[last]->panel->Top;
					last++;
					if(last >= size){last=0;}
				} 
				
			}

Would you be able to help with the code. It would be much aprecieated. Thanks.

Re: Animating a snake (aka Snafu)

Richard Andrew x6427-Mar-11 16:24

Richard Andrew x64

27-Mar-11 16:24

I think the problem might be that you're not keeping track of which panel is at the head of the snake, since movement is referenced against the head panel.

The code might go something like this: ( I have not tested this code. It might need modification. )

if ( y2 == -1 ) // Move down
{
    segments[last]->panel->Top = y + segments[head]->panel->Top + 2;
    segments[last]->panel->Left = segments[head]->panel->Left;

    head = last;
    last++;
    if ( last >= size )
    {
        last = 0;
    }

}

The difficult we do right away...
...the impossible takes slightly longer.

Re: Animating a snake (aka Snafu)

Cyclone_S28-Mar-11 14:21

Cyclone_S

28-Mar-11 14:21

You are correct, that's what the problem was. The snake is now moving in all directions. Thanks for helping me out. Smile | :)

Re: Animating a snake (aka Snafu)

Cyclone_S30-Mar-11 14:22

Cyclone_S

30-Mar-11 14:22

One last thing. I got the collision function working 99% but there's a small glitch where if
the head collides with the tail the collision function doesn't catch it and the snake keeps moving.

The collision function.

void check_for_collision()
			{
				for(int Tail = 0; Tail <= (size-1); Tail++)
				{
					for(int I = 0;I <= (size-1); I++)
					{
						if(I != head){segments[I]->panel->BackColor= Color::Blue;} else
						{
							segments[head]->panel->BackColor= Color::Yellow; // Color the head a different yellow.
						}

						if(head!= Tail && segments[head]->panel->Left == segments[Tail]->panel->Left && segments[head]->panel->Top == segments[Tail]->panel->Top) // Detect a collision is segments overlap.
						{
							segments[head]->panel->BackColor= Color::Red;
							Timer1->Stop();
						}
					
					}
				}
			}

Entire code.

#include "stdafx.h"
using namespace System;
using namespace System::Drawing;
using namespace System::Windows::Forms;
using namespace System::Collections::Generic; // Required to make lists.

public ref class snake_segment
{
	public:
			Panel^ panel; // A Panel is used to make the snake.

			snake_segment( Form ^ form ) // Class Constructor.
			{ 
				
				panel = gcnew Panel();
				//panel->BackColor= Color::Blue;
				panel->Width = 20; panel->Height = 20;
				form->Controls->Add(panel);
			}
};

public ref class Form1 : public Form 
{
	public:
			List<snake_segment^>^ segments; // A list that contains the snake segments.
			int l; // Length of the snake at begining of game.
			int size; // The number of segments in snake/list.
			int tail;  // The tail segment of the snake.
			int head;  // The head segment of the snake.
			int x, y; // The coordinates of the snake segment(head).
			int direction; // Stores the direction the snake will move.
			Timer^ Timer1; // The timer that will move the snake.
			bool game_started;
			

			Form1() // Class constructor.
			{	
				segments = gcnew List<snake_segment^>();
				Timer1 = gcnew Timer();
				Timer1->Interval = 500;
				Timer1->Start();
				Timer1->Tick += gcnew System::EventHandler(this, &Form1::timer1_Tick);
				this->KeyDown += gcnew System::Windows::Forms::KeyEventHandler(this, &Form1::Form_KeyDown);
				Make_Snake();
			}
			
			void Make_Snake()
			{
				for(int I = 0; I <= 5; I++)
				{
					snake_segment^ s = gcnew snake_segment(this);
					s->panel->BackColor = Color::FromArgb(0,0,255);
					segments->Add(s);
				}

				for each (snake_segment^ s in segments) // Position the segments at start of game.
				{
					l += s->panel->Width + 2;
					s->panel->Left = l;
				}
				get_size_of_snake();
				segments[size-1]->panel->BackColor= Color::Yellow; // Color the head yellow.
			}

			void get_size_of_snake() // Get the size of the snake when a new segment is added by eating something etc.
			{
				size=0;
				for each (snake_segment^ s in segments)
				{
					size++;	
				}
				head=size-1;
			}

			void head_position() // The head position at start of game.
			{
				x = segments[size-1]->panel->Left;
				y = segments[size-1]->panel->Top;
			}

			void move_snake()
			{
				if(direction==1) // Move snake left.
				{
					segments[tail]->panel->Location = Drawing::Point(x - 20 - 2,y); // Note using "Location" instead of "Left/Top" solved a problem where the segment would flicker as it's being moved to the head position.
					head = tail;
					x = segments[head]->panel->Left;
					y = segments[head]->panel->Top;
					tail++;
					if(tail >= size){tail=0;}
				}

				if(direction==-1) // Move snake right.
				{
					segments[tail]->panel->Location = Drawing::Point(x + 20 + 2,y);
					head = tail;
					x = segments[head]->panel->Left;
					y = segments[head]->panel->Top;
					tail++;
					if(tail >= size){tail=0;}
				}

				if(direction==2) // Move snake up;
				{
					segments[tail]->panel->Location = Drawing::Point(x,y - 20 - 2);
					head = tail;
					x = segments[head]->panel->Left;
					y = segments[head]->panel->Top;
					tail++;
					if(tail >= size){tail=0;}
				}
				
				if(direction==-2) // Move snake down;
				{
					segments[tail]->panel->Location = Drawing::Point(x,y + 20 + 2);
					head = tail;
					x = segments[head]->panel->Left;
					y = segments[head]->panel->Top;
					tail++;
					if(tail >= size){tail=0;}
				}
				
			}

			void check_for_collision()
			{
				for(int Tail = 0; Tail <= (size-1); Tail++)
				{
					for(int I = 0;I <= (size-1); I++)
					{
						if(I != head){segments[I]->panel->BackColor= Color::Blue;} else
						{
							segments[head]->panel->BackColor= Color::Yellow; // Color the head a different yellow.
						}

						if(head!= Tail && segments[head]->panel->Left == segments[Tail]->panel->Left && segments[head]->panel->Top == segments[Tail]->panel->Top) // Detect a collision is segments overlap.
						{
							segments[head]->panel->BackColor= Color::Red;
							Timer1->Stop();
						}
					
					}
				}
			}

			System::Void timer1_Tick(System::Object^  sender, System::EventArgs^  e) // A timer that will move the snake;
			{
				
				if(!game_started){head_position();game_started=true;} // Find first head position at start of game.
				move_snake();
				check_for_collision();
			}

			System::Void Form_KeyDown(System::Object^ sender, System::Windows::Forms::KeyEventArgs^ e)
			{
				if(e->KeyCode == Keys::Left){direction=1;}
				if(e->KeyCode == Keys::Right){direction=-1;}
				if(e->KeyCode == Keys::Up){direction=2;}
				if(e->KeyCode == Keys::Down){direction=-2;}

				if(e->KeyCode == Keys::Space) // Add a new segment to the snake.
				{
					snake_segment^ s = gcnew snake_segment(this);
					segments->Insert(tail,s);
					head = tail;
					segments[tail]->panel->Location = Drawing::Point(x + segments[head]->panel->Width + 2,y); 
					x = segments[head]->panel->Left;
					y = segments[head]->panel->Top;
					tail++;
					get_size_of_snake();
					if(tail >= size){tail=0;}
				}	
			}
};

[STAThread]
int main()
{
    Application::Run(gcnew Form1());
}

Thanks.

Re: Animating a snake (aka Snafu)

Richard Andrew x6430-Mar-11 15:41

Richard Andrew x64

30-Mar-11 15:41

I think you should simplify the collision function. I don't think you need two loops.

If you want to check whether the head is colliding with any of the other segments, then just do:

for (int ThisSegment = 0; ThisSegment < (size-1); ThisSegment ++ )
{
    if ( ThisSegment == head ) continue;

    if ( segments[ThisSegment]->panel->Left == segments[head]->panel->Left &&
         segments[ThisSegment]->panel->Top  == segments[head]->panel->Top )
    {
        Timer->Stop();
    }
}

The difficult we do right away...
...the impossible takes slightly longer.

Re: Animating a snake (aka Snafu)

Cyclone_S31-Mar-11 10:14

Cyclone_S

31-Mar-11 10:14

Thanks. Thats much simpler code then what I had.

Re: Animating a snake (aka Snafu)

Cyclone_S16-Apr-11 9:44

Cyclone_S

16-Apr-11 9:44

Hi Richard. I was wondering if you would be able to help me with a bit of code. I posted it here. Thank You.

[Algorthm][^]

issue while loading MFC extension dll dynamically

ptr_Electron25-Mar-11 0:37

ptr_Electron

25-Mar-11 0:37

I had MFC dll which exposes some clases. I would like to load this dll dynamically.

hResult = LoadLibrary(_T("c:\test.dll));
if (0 != hResult)
{
		_InitSomeDLLFun = (InitSomeDLL)::GetProcAddress(hResult, "InitSomeDLL");
// always Undefind value is returned by GetProcAddress
																		  
		if(_InitSomeDLL)
		{
			_InitSomeDLLFun();
		}
		err = GetLastError();

}

Please advice

Re: issue while loading MFC extension dll dynamically

Richard MacCutchan25-Mar-11 1:02

Richard MacCutchan

25-Mar-11 1:02

What error is returned? Have you checked that InitSomeDLL is exported by your DLL and is not a mangled C++ name?

I must get a clever new signature for 2011.

Re: issue while loading MFC extension dll dynamically

ptr_Electron25-Mar-11 1:21

ptr_Electron

25-Mar-11 1:21

The LoadLibrary() call was sucessfull, but
GetProcAddress() always returns <undefind value="">

the dlls are unmanaged dlls.

Please advice

Re: issue while loading MFC extension dll dynamically

Richard MacCutchan25-Mar-11 2:03

Richard MacCutchan

25-Mar-11 2:03

Very interesting, but you didn't answer my questions.

I must get a clever new signature for 2011.

Re: issue while loading MFC extension dll dynamically

ptr_Electron25-Mar-11 3:50

ptr_Electron

25-Mar-11 3:50

GetLastError() after the GetProcAddress returnts error code: 127

Re: issue while loading MFC extension dll dynamically

Richard MacCutchan25-Mar-11 5:24

Richard MacCutchan

25-Mar-11 5:24

Did you bother to look up error code 127 to see what it indicates? I guess not; see here[^] for more information. Now you know what's wrong you can probably make a start at fixing it.

I must get a clever new signature for 2011.

Instances of an object

Cyclone_S19-Mar-11 16:47

Cyclone_S

19-Mar-11 16:47

Hi,

I'm currently making a simple game. Pressing the down arrow places a box on the form. Pressing up shoots missiles(blue boxes) and creates multiple instances of m1 which is part of the missle class.

What I want to do is change the color of each missle as it collides with the red box. So far only the last missile changes color. The other instances of the missle class get ignored.

#include "stdafx.h"
using namespace System;
using namespace System::Drawing;
using namespace System::Windows::Forms;

public ref class object
{
	public:
			PictureBox^ Box3;
			
			object( Form ^ form ) // Class Constructor.
			{
				Box3 = gcnew PictureBox();
				Box3->Left = 150;
				Box3->Top = 50;
				Box3->Width = 100;
				Box3->Height = 100;
				Box3->BackColor = System::Drawing::Color::Red;
				form->Controls->Add(Box3);
			}
};

public ref class missile
{
	public:
			PictureBox^ Box1;
			Timer^ Timer1;

			missile( Form ^ form ) // Class Constructor.
			{
				Timer1 = gcnew Timer;
				Timer1->Interval = 1;
				Timer1->Start();
				Box1 = gcnew PictureBox();
				Box1->Left = 150;
				Box1->Top = 240;
				Box1->Width = 10;
				Box1->Height = 10;
				Box1->BackColor = System::Drawing::Color::Blue;
				form->Controls->Add(Box1);
				Timer1->Tick += gcnew System::EventHandler(this, &missile::timer1_Tick);
			}

		System::Void timer1_Tick(System::Object^  sender, System::EventArgs^  e)
		{
			Box1->Top -= 1;
		}
};


public ref class Form1 : public Form 
{
	public:
			PictureBox^ Box2;
			missile^ m1;
			object^ o1;
			Timer^ Timer3;
			bool x;

			Form1() // Class constructor.
			{	
				x=false;
				Timer3 = gcnew Timer();
				Timer3->Interval = 1;
				Timer3->Start();
				Box2 = gcnew PictureBox();
				Box2->BackColor = Color::Blue;
				Box2->Top = 240;
				Box2->Left = (this->Width / 2) - 40;
				Box2->Width = 40;
				Box2->Height = 10;
				this->Controls->Add(Box2);
				this->KeyDown += gcnew System::Windows::Forms::KeyEventHandler(this, &Form1::Form_KeyDown);
				Timer3->Tick += gcnew System::EventHandler(this, &Form1::timer3_Tick);
			}

			System::Void Form_KeyDown(System::Object^ sender, System::Windows::Forms::KeyEventArgs^ e)
			{	
				if(e->KeyCode == Keys::Up){x=true;m1 = gcnew missile(this);m1->Box1->Left = Box2->Left + (Box2->Width / 2) - 10;}
				if(e->KeyCode == Keys::Left){Box2->Left -= 4;}
				if(e->KeyCode == Keys::Right){Box2->Left += 4;}
				if(e->KeyCode == Keys::Down) {o1 = gcnew object(this); }
			}

			System::Void timer3_Tick(System::Object^  sender, System::EventArgs^  e)
			{
				if(x==true)
				{
					if(m1->Box1->Top == o1->Box3->Bottom){m1->Box1->BackColor = Color::Green;}
				}
			}

			bool isColliding(PictureBox^ box1, PictureBox^ box3)
			{
				Rectangle r1 = m1->Box1->Bounds;
				Rectangle r2 = o1->Box3->Bounds;
				return r1.IntersectsWith(r2); //return true if they collide
			}
			
};


[STAThread]
int main()
{	
    Application::Run(gcnew Form1());
}

I also am trying to figure out how to remove the instances from memory after a set amount of time as too many instances slows the program.

Thanks for the help.

Re: Instances of an object

John Schroedl19-Mar-11 18:51

John Schroedl

19-Mar-11 18:51

I think your real slowdown comes from having a timer in each individual missiles. They keep ticking even after they've left the screen. And you never stop the timer and unsubscribe the tick event in each missile. This keeps the timers and missiles all alive all the time.

I've tweaked your code some and removed those separate timers and just update all the missiles from the Form's timer. Also, I remove the missiles which have gone off-screen so those won't be updated after they're gone . This should allow for more missiles and better perf/memory usage.

There are clearly other improvements you could do such as having the logic to determine whether a missile is off-screen determined by the missile class.

I hope this helps you get going...

John

using namespace System;

using namespace System::ComponentModel;
using namespace System::Collections;
using namespace System::Windows::Forms;
using namespace System::Data;
using namespace System::Drawing;

using namespace System::Collections::Generic;

public ref class object{	
	public:			
		PictureBox^ Box3;						
		
		object( Form ^ form ) // Class Constructor.			
		{				
			Box3 = gcnew PictureBox();				
			Box3->Left = 150;				
			Box3->Top = 50;				
			Box3->Width = 100;				
			Box3->Height = 100;				
			Box3->BackColor = System::Drawing::Color::Red;				
			form->Controls->Add(Box3);			
		}
};

public ref class missile{	
	public:			
		PictureBox^ Box1;			
		
		missile( Form ^ form ) // Class Constructor.			
		{				
			Box1 = gcnew PictureBox();				
			Box1->Left = 150;				
			Box1->Top = 240;				
			Box1->Width = 10;				
			Box1->Height = 10;				
			Box1->BackColor = System::Drawing::Color::Blue;				
			form->Controls->Add(Box1);				
		}		
		
		void update()
		{
			Box1->Top--;
		}
};

public ref class Form1 : public System::Windows::Forms::Form
{
public:		
	PictureBox^ Box2;			
	object^ o1;			
	Timer^ Timer3;			
	bool x;			
	List<missile^>^ Missiles;
		
	Form1() // Class constructor.			
	{		
		Missiles = gcnew List<missile^>();

		x=false;				
		Timer3 = gcnew Timer();				
		Timer3->Interval = 1;				
		Timer3->Start();				
		Box2 = gcnew PictureBox();				
		Box2->BackColor = Color::Blue;				
		Box2->Top = 240;				
		Box2->Left = (this->Width / 2) - 40;				
		Box2->Width = 40;				
		Box2->Height = 10;				
		this->Controls->Add(Box2);				
		this->KeyDown += gcnew System::Windows::Forms::KeyEventHandler(this, &Form1::Form_KeyDown);				
		Timer3->Tick += gcnew System::EventHandler(this, &Form1::timer3_Tick);			
	}			
		
	System::Void Form_KeyDown(System::Object^ sender, System::Windows::Forms::KeyEventArgs^ e)			
	{					
		if(e->KeyCode == Keys::Up)
		{
			x=true;
			missile^ m = gcnew missile(this);
			m->Box1->Left = Box2->Left + (Box2->Width / 2) - 10;
			Missiles->Add(m);
		}				
			
		if(e->KeyCode == Keys::Left) {Box2->Left -= 4; }							
		if(e->KeyCode == Keys::Right){Box2->Left += 4; }				
		if(e->KeyCode == Keys::Down) {o1 = gcnew object(this); }			
	}			
		
	bool IsMissileOffScreen(missile^ m)
	{
		return m->Box1->Bottom < 0;
	};

	System::Void timer3_Tick(System::Object^  sender, System::EventArgs^  e)			
	{		
		for each (missile^ m in Missiles)
		{
			m->update();
				if(x==true && o1 != nullptr)				
			{					
				if (m->Box1->Top == o1->Box3->Bottom)
				{
					m->Box1->BackColor = Color::Green;
				}				
			}	
		}

		Missiles->RemoveAll(gcnew Predicate<missile^>(this, &Form1::IsMissileOffScreen));
	}			
		
	bool isColliding(PictureBox^ box1, PictureBox^ box3)			
	{	
		Rectangle r2 = o1->Box3->Bounds;				
		for each (missile^ m in Missiles)
		{
			Rectangle r1 = m->Box1->Bounds;				
			if (r1.IntersectsWith(r2)) //return true if they collide		
				return true;
		}
		return false;
	}			
};

Re: Instances of an object

John Schroedl19-Mar-11 19:01

John Schroedl

19-Mar-11 19:01

Also, if you want to detect a collision, change the logic in the timer tick:

System::Void timer3_Tick(System::Object^  sender, System::EventArgs^  e)
{
    for each (missile^ m in Missiles)
    {
        m->update();

        if(x==true && o1 != nullptr)
        {
            if (o1->Box3->Bounds.IntersectsWith(m->Box1->Bounds))
            {
                m->Box1->BackColor = Color::Green;
            }
        }
    }

    Missiles->RemoveAll(gcnew Predicate<missile^>(this, &Form1::IsMissileOffScreen));
}

Other advice: It would be courteous to let us know that you've posted about this in the C++ forum as well to prevent duplication of efforts.

John

Re: Instances of an object

Cyclone_S20-Mar-11 10:56

Cyclone_S

20-Mar-11 10:56

Thanks for the help.

how would I go about deleting m1,m2 in my original code? Not sure how to delete the m1,m2 objects. I currently have something like this.

if(e->KeyCode == Keys::Up) // Check if m1,m2 objects exist or not. If they don't then create them.
				{
					mcount += 1;
					l1->Text = mcount.ToString();
					if(mcount == 1 && !m1){mcount1 = true; m1 = gcnew missile(this);m1->Box1->Left = Box2->Left + (Box2->Width / 2) - 10;}
					if(mcount == 2 && !m2){mcount=0;mcount2 = true;m2 = gcnew missile(this);m2->Box1->Left = Box2->Left + (Box2->Width / 2) - 10;}
					if(mcount == 2){mcount=0;}

Re: Instances of an object

Luc Pattyn20-Mar-11 11:47

Luc Pattyn

20-Mar-11 11:47

The easiest way is to keep only real missiles in your collection, which means:
- the collection starts off empty;
- when you create a missile, add it to the collection;
- when you destroy a missile, remove it from the collection.

Avoid overall variables (such as mcount in your example), as they typically are redundant and hence just can cause bugs and inconsistencies.

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles] Nil Volentibus Arduum

Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

Re: Instances of an object

Cyclone_S20-Mar-11 15:47

Cyclone_S

20-Mar-11 15:47

Thanks.

John a have a few questions about your code.

1.

Missiles->RemoveAll(gcnew Predicate<missile^>(this, &Form1::IsMissileOffScreen));

How exactly does this work.

2. What does the ^ character do.

Thanks again.

Re: Instances of an object

Luc Pattyn20-Mar-11 15:50

Luc Pattyn

20-Mar-11 15:50

Oops. You replied to me, not to John. I suggest you try again.

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles] Nil Volentibus Arduum

Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

Re: Instances of an object

Cyclone_S20-Mar-11 16:30

Cyclone_S

20-Mar-11 16:30

Thanks.

John a have a few questions about your code.

1.
Missiles->RemoveAll(gcnew Predicate<missile^>(this, &Form1::IsMissileOffScreen));How exactly does this work.

2. What does the ^ character do.

Thanks again.

Re: Instances of an object

John Schroedl21-Mar-11 5:02

John Schroedl

21-Mar-11 5:02

Let's start with #2:

The ^ character indicates a handle which is a reference to a managed object on the CLI heap.

The Wikipedia article isn't too good at explaining in my opinion: http://en.wikipedia.org/wiki/C%2B%2B/CLI#Handles[^] but you may want to look at it anyway.

This intro may be a bit friendlier: http://www.functionx.com/cppcli/handles/Lesson06c.htm[^]

For #1:

I'm creating a Predicate which is really just a function which returns True or False based on my own rules. Often predicates are used for sorting.

So my predicate function (IsMissileOffScreen) returns True if I see the missile has left the screen.

In RemoveAll, my predicate is called and passed one missile at a time as a parameter (the type of the parameter is missile^ which I indicate in the < > arguments. If I return True from IsMissileOffScreen, the RemoveAll() call will remove the missile from the Missiles list. So after this line, we're left with only on-screen missiles in the Missiles list.

Make sense?

John

Re: Instances of an object

Cyclone_S21-Mar-11 16:44

Cyclone_S

21-Mar-11 16:44

Yea it mostly makes sense. I apreciate the help.

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