FastReport4开发者手册：组件与定制指南

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"FastReport4 Developer's Manual 是一本关于FastReport4开发的手册，由FastReports Inc.出版，涵盖了从1998年至2012年的内容。手册旨在帮助开发者深入理解和定制FastReport4的各种组件，提升报表设计和开发能力。" 在手册中，FastReport4的类层次结构是首要介绍的部分，它详细阐述了FastReport的所有组件是如何基于"TfrxComponent"这个基类构建的。"TfrxComponent"是所有FastReport组件的基础，它拥有如坐标、大小、字体和可见性等属性，并且维护了下属对象的列表。此类还包含了用于保存和恢复对象状态到或从流中的方法，这对手动序列化和反序列化组件状态至关重要。接下来，手册深入介绍了如何编写自定义报告组件，这是FastReport4灵活性的核心。开发者可以扩展其功能，创建独特的报表元素，以满足特定需求。这部分内容可能包括了组件的设计、事件处理、属性设置等方面的知识。在"WritingCustomCommonControls"章节中，手册教导读者如何定制通用控件，这可能是为了提供新的用户交互方式或实现特定的显示效果。这涉及到对控件行为的理解和重写，以及可能的绘图操作。 "EventHandlerDescription"部分则详细解释了事件处理器的工作机制，这对于响应用户交互和动态更新报表是必不可少的。开发者将学习如何绑定和编写事件处理代码，以实现动态报告功能。 "ComponentRegistrationinScriptSystem"探讨了如何在脚本系统中注册自定义组件，这使得在运行时可以通过脚本语言控制这些组件，增加了报表的动态性和可编程性。 "WritingComponentEditors"和"WritingPropertyEditors"章节聚焦于组件编辑器和属性编辑器的开发，这有助于在设计时提供更好的用户体验，使得在IDE中配置组件变得更加直观和高效。 "WritingCustomDBEngines"部分则面向更高级的开发者，它展示了如何创建自定义的数据库引擎，这可能涉及到与不同数据源的集成，支持新的SQL语法或者提供特殊的查询功能。 "UsingCustomFunctionsinaReport"章节介绍了如何在报表中使用自定义函数，这扩展了报表计算和逻辑处理的能力，使得报告能够执行更复杂的业务逻辑。最后，"WritingCustomWizards"可能讲述了如何构建自定义向导，帮助用户快速生成或配置报表，提高工作效率。这本FastReport4 Developer's Manual是一份详尽的参考资料，涵盖了FastReport4开发的各个方面，对于想要深入理解和定制FastReport4的开发者来说，它是不可或缺的学习工具。通过学习手册中的内容，开发者能够提升报表设计和开发技能，创造出更加高效、功能丰富的报表解决方案。

6 FastReport 4 Developer's manual

published

property StretchMode: TfrxStretchMode;

end;

Objects of this class can be stretched vertically and also split into smaller pieces when the

objects don't have sufficient width on the output page. The objects are split enough times to fit

all of their data into the available space.

The following methods are defined in this class:

- CalcHeight calculates and returns object height according to the data placed in it

- InitPart called before object splitting

- DrawPart draws next data chunk placed in object

“Return value” is the amount of unused space where it was impossible

to display data

7Writing Custom Report Components

Writing Custom Report Components

FastReport has a large number of components that can be placed on a report design page.

They are: text, picture, line, geometrical figure, OLE, rich text, bar code, diagram etc. You can

also write your own custom component and then attach it to FastReport.

FastReport has several classes from which components can be inherited. For more details,

see “FastReport Class Hierarchy”. The TfrxView class is of primary interest, since most report

components are inherited from it.

As a minimum the “Draw” method in the TfrxReportComponent base class should be defined.

procedure Draw(Canvas: TCanvas;

ScaleX, ScaleY, OffsetX, OffsetY: Extended); virtual;

This method is called when the component is painted in the designer, in the preview window

and during output printing. TfrxView overrides this method for drawing the object frame and

background. This method should draw the component's contents on the “Canvas” drawing

surface. The object coordinates and sizes are stored in the “AbsLeft”, “AbsTop” and “Width”,

“Height” properties respectively.

The “ScaleX” and “ScaleY” parameters define the object scaling in the X-axis and Y-axis

respectively. These parameters equal 1 at 100% zoom and can change if the user modifies

zooming either in the designer or in the preview window. The “OffsetX” and “OffsetY”

parameters shift the object along the X-axis and Y-axis. So, taking all these parameters into

account the upper left corner coordinate will be:

X := Round(AbsLeft * ScaleX + OffsetX);

Y := Round(AbsTop * ScaleY + OffsetY);

To simplify operations with coordinates, the “BeginDraw” method (with parameters similar to

“Draw”) is defined in the “TfrxView” class.

procedure BeginDraw(Canvas: TCanvas;

ScaleX, ScaleY, OffsetX, OffsetY: Extended); virtual;

This method should be called in the first line of the “Draw” method. It transforms the

coordinates into FX, FY, FX1, FY1, FDX, FDY and FFrameWidth integer values, which can be

used later in TCanvas methods. It also copies Canvas, ScaleX and ScaleY values into the

FCanvas, FScaleX and FScaleY variables, which can be referred to in any class method.

There are also two methods in the TfrxView class for drawing object backgrounds and frames.

procedure DrawBackground;

procedure DrawFrame;

The BeginDraw method should be called before calling these two methods.

Let's look at how to create a component which will display an arrow.

type

TfrxArrowView = class(TfrxView)

public

{ we should override only two methods }

procedure Draw(Canvas: TCanvas;

ScaleX, ScaleY, OffsetX, OffsetY: Extended); override;

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