ASP.NET Web PDF Document Viewer/Editor Control Library

Nonetheless, it is useful to have a common conceptual language for describing our systems and the common characteristics of the code we use to implement them. Equally, when you are looking at someone else s code (remembering that someone else includes past you ) it is helpful to be able to translate what was written into these standard modeling concepts. So we have a software model of the Firetruck, which has a Ladder and a Hose and uses a Firefighter as its Driver. What about the fire chief The fire chief is just another firefighter. He can drive a truck. He can put out fires. But he can do other stuff too. For instance, he can delegate responsibility for putting out a fire to another firefighter. The question we ask ourselves is this: is the FireChief a Firefighter with extra responsibilities If the answer is yes, we are describing an is-a association (the FireChief is a Firefighter) which we can represent by an inheritance relationship.

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Note It is possible to set several colors at different points; set the end colors to show the effect in a

We ll get into the nuances of the question in the preceding paragraph in a minute, but let s assume for the time being that our answer to the question is yes (which, on face value, seems reasonable). Example 4-3 shows how we use inheritance in C#.

class FireChief : Firefighter { public void TellFirefighterToExtinguishFire (Firefighter colleague) { colleague.ExtinguishFire(); } }

Notice that we use the colon in the class declaration to indicate that FireChief is a Firefighter. We then say that Firefighter is a base class of FireChief. Looking at the relationship from the other direction, we can also say that FireChief is a derived class of Firefighter. We ve added the extra function that allows the chief to tell a firefighter to extinguish a fire which encapsulates that extra responsibility. What we haven t had to do is to duplicate all the functionality of the firefighter; that comes along anyway. We can now use the fire chief just as we would a firefighter, as shown in Example 4-4.

Listing 7-7. Setting up gradients QLinearGradient linGrad( QPointF(80, 80), QPoint( 120, 120 ) ); linGrad.setColorAt( 0, Qt::black ); linGrad.setColorAt( 1, Qt::white ); ... QRadialGradient radGrad( QPointF(100, 100), 30 ); radGrad.setColorAt( 0, Qt::black ); radGrad.setColorAt( 1, Qt::white ); ... QConicalGradient conGrad( QPointF(100, 100), -45.0 ); conGrad.setColorAt( 0, Qt::black ); conGrad.setColorAt( 1, Qt::white ); To use one of the gradients as a brush, simply pass the QGradient object to the QBrush constructor. Gradient brushes are not affected by calls to the setColor method of the QBrush object. The last way to create a brush is to pass a QPixmap or a QImage object to the QBrush constructor or to call setTexture on a QBrush object. This process makes the brush use the given image as a texture and fill any shape by repeating the pattern (an example is shown in Figure 7-17).

Firetruck truckOne = new Firetruck(); FireChief bigChiefHarry = new FireChief { Name = "Harry" }; truckOne.Driver = bigChiefHarry; bigChiefHarry.Drive(truckOne, new Point(100,300));

Firefighter joe = new Firefighter { Name = "Joe" }; bigChiefHarry.TellFirefighterToExtinguishFire(joe);

Because bigChiefHarry is an object of type FireChief, and a FireChief is a Fire fighter, we can assign him to be the driver of a truck and tell him to drive it somewhere. But because he is a FireChief, we can also ask him to tell Joe to put out the fire when he gets there. Wherever we talk about a FireChief, we can treat the object as a Firefighter. This use of one type as though it were one of its bases is an example of polymorphism. Equally, we could phrase that the other way around: we can successfully substitute an instance of a more-derived class where we expect a base class. This is known as the Liskov Substitution Principle (LSP) after computer scientist Barbara Liskov, who articulated the idea in a paper she delivered in 1987.

The ScriptManagerProxy control is available as an additional script manager for a page. Only one ScriptManager control is allowed, and if you, for example, place a ScriptManager control on a master page but need to add script references to your content page, then you can use the ScriptManagerProxy control. So, if you have the following master page: <%@ Master Language="C#" AutoEventWireup="true" CodeFile="MasterPage.master.cs" Inherits="MasterPage" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" > <head runat="server"> <title>Untitled Page</title> </head> <body> <form id="form1" runat="server"> <div> <atlas:ScriptManager ID="ScriptManager1" runat="server"> </atlas:ScriptManager> This is the Master Page.<br /> It contains this ScriptManager control:<br /> <br /> <asp:contentplaceholder id="ContentPlaceHolder1" runat="server"> <br /> </asp:contentplaceholder>   </div> </form> </body> </html> and you create a new content page based on this master page, your new page will look like this at design time: <%@ Page Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true" CodeFile="Default3.aspx.cs" Inherits="Default3" Title="Untitled Page" %> <asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server"> </asp:Content> When you run this page and look at the source code that is generated by ASP .NET from this design-time definition, you will see this:

As you learned during the discussion of global (device) coordinates and local (widget) coordinates, Qt can use different coordinate systems for different areas of the screen. The difference between the global and local coordinates is that the origin, the point (0,0), has been moved. In technical terms, this is known as translating the coordinate system.