关于如何使用位图在2.4 在窗口中绘制设备相关位图，图标，设备无关位图中会详细讲解。还有一种特殊的GUI对象是多边形，利用多边形可以很好的限制作图区域或是改变窗口外型。关于如何创建和使用多边形在2.6 多边形和剪贴区域中会详细讲解。在Windows中使用GUI对象必须遵守一定的规则。首先需要创建一个合法的对象，不同的对象创建方法不同。然后需要将该GUI对象选入DC中，同时保存DC中原来的GUI对象。如果选入一个非法的对象将会引起异常。在使用完后应该恢复原来的对象，这一点特别重要，如果保存一个临时对象在DC中，而在临时对象被销毁后可能引起异常。有一点必须注意，每一个对象在重新创建前必须销毁，下面的代码演示了这一种安全的使用方法：
OnDraw(CDC* pDC) { CPen pen1,pen2; pen1.CreatePen(PS_SOLID,2,RGB(128,128,128));//创建对象 pen2.CreatePen(PS_SOLID,2,RGB(128,128,0));//创建对象 CPen* pPenOld=(CPen*)pDC->SelectObject(&pen1);//选择对象进DC drawWithPen1... (CPen*)pDC->SelectObject(&pen2);//选择对象进DC drawWithPen2... pen1.DeleteObject();//再次创建前先销毁 pen1.CreatePen(PS_SOLID,2,RGB(0,0,0));//再次创建对象 (CPen*)pDC->SelectObject(&pen1);//选择对象进DC drawWithPen1... pDC->SelectObject(pOldPen);//恢复 }
此外系统中还拥有一些库存GUI对象，你可以利用
CDC::SelectStockObject(SelectStockObject( int nIndex )选入这些对象，它们包括一些固定颜色的刷子，画笔和一些基本字体。
? ? ? ? ? ? ? ?
BLACK_BRUSH Black brush. DKGRAY_BRUSH Dark gray brush. GRAY_BRUSH Gray brush. HOLLOW_BRUSH Hollow brush. LTGRAY_BRUSH Light gray brush. NULL_BRUSH Null brush. WHITE_BRUSH White brush. BLACK_PEN Black pen.
? ? ? ? ? ? ?
NULL_PEN Null pen. WHITE_PEN White pen.
ANSI_FIXED_FONT ANSI fixed system font. ANSI_VAR_FONT ANSI variable system font. DEVICE_DEFAULT_FONT Device-dependent font. OEM_FIXED_FONT OEM-dependent fixed font.
SYSTEM_FONT The system font. By default, Windows uses the system font to draw menus, dialog-box controls, and other text. In Windows versions 3.0 and later, the system font is proportional width; earlier versions of Windows use a fixed-width system font.
? SYSTEM_FIXED_FONT The fixed-width system font used in Windows prior to version 3.0. This object is available for compatibility with earlier versions of Windows.
? DEFAULT_PALETTE Default color palette. This palette consists of the 20 static colors in the system palette.
这些对象留在DC中是安全的，所以你可以利用选入库存对象来作为恢复DC中GUI对象。 大家可能都注意到了绘图时都需要一个DC对象，DC（Device Context设备环境）对象是一个抽象的作图环境，可能是对应屏幕，也可能是对应打印机或其它。这个环境是设备无关的，所以你在对不同的设备输出时只需要使用不同的设备环境就行了，而作图方式可以完全不变。这也就是Windows耀眼的一点设备无关性。如同你将对一幅画使用照相机或复印机将会产生不同的输出，而不需要对画进行任何调整。DC的使用会穿插在本章中进行介绍。
c++继承经典例子 #include
class Base {
private:
int b_number; public:
Base( ){}
Base(int i) : b_number (i) { } int get_number( ) {return b_number;}
void print( ) {cout << b_number << endl;} };
class Derived : public Base {
private:
int d_number; public:
// constructor, initializer used to initialize the base part of a Derived object. Derived( int i, int j ) : Base(i), d_number(j) { };
// a new member function that overrides the print( ) function in Base void print( ) {
cout << get_number( ) << \ // access number through get_number( ) cout << d_number << endl; } };
int main( ) {
Base a(2);
Derived b(3, 4);
cout << \
a.print( ); // print( ) in Base cout << \
b.print( ); // print( ) in Derived cout << \
b.Base::print( ); // print( ) in Base
return 0; }
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没有虚析构函数，继承类没有析构
//Example: non- virtual destructors for dynamically allocated objects. #include
class Thing { public:
virtual void what_Am_I( ) {cout << \
~Thing(){cout<<\};
class Animal : public Thing { public:
virtual void what_Am_I( ) {cout << \~Animal(){cout<<\};
void main( ) {
Thing *t =new Thing; Animal*x = new Animal; Thing* array[2];
array[0] = t; // base pointer array[1] = x;
for (int i=0; i<2; i++) array->what_Am_I( ) ;
delete array[0]; delete array[1]; return ; }
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纯虚函数，多态 #include
class Point {
private:
double x; double y; public:
Point(double i, double j) : x(i), y(j) { } void print( ) const
{ cout << \};
class Figure
{
private:
Point center; public:
Figure (double i = 0, double j = 0) : center(i, j) { } Point& location( ) {
return center;
} // return an lvalue void move(Point p) {
center = p; draw( ); }
virtual void draw( ) = 0; // draw the figure virtual void rotate(double) = 0; // rotate the figure by an angle };
class Circle : public Figure {
private:
double radius; public:
Circle(double i = 0, double j = 0, double r = 0) : Figure(i, j), radius(r) { } void draw( ) {
cout << \ circle with center \ location( ).print( );
cout << \ }
void rotate(double) {
cout << \ } // must be defined };
class Square : public Figure
{
private:
double side; // length of the side
C++学习笔记与开发技巧与典型列子
