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Tham gia thực hiện điều tương tự như tất cả các vòng lặp logic và thao tác biến chứng minh trước đó, với chức năng đơn giản. Ngược lại, bạn có thể muốn có một giá trị chuỗi biến có chứađược tạo ra trong báo cáo, cho phép duy nhất, nhiều, và / hoặc thay đổi giá trị tham số. | 594 Crystal Reports 9 The Complete Reference RAS SDK Model View Controller Architecture The RAS SDK object model differs substantially from the RDC in both architecture and syntax. The first substantial difference is the way objects are organized and exposed. While the RDC is relatively flat exposing only a few high-level objects such as the Application object and the Report object RAS takes a different view of object orientation by introducing a Model View Controller or MVC architecture. MVC ÍS a design paradigm often applied to application or development environments that separates application elements into three parts Model View and Controller. When attempting to fit the RAS SDK into this architecture you can consider the three members of MVC to approximate to RAS in this way View The end-user view of the report this is designed by you the developer and presented to the end user in the user s browser. Model All possible properties of a report generally available in a read-only mode. The model exposes the names of fields groups formulas report objects and sections and so forth. Controller All report objects that can be deleted added or modified. For the most part however you cannot query a controller to find out the existing status of a report object. To put the MVC architecture in more of a real-world perspective for the RAS developer the View is the custom application the Model is where you get existing report properties and the Controller is where you change report properties. Probably the most important point here is that you must use a Controller to modify report properties you can t do it with the Model. To further define the RAS SDK architecture look at Table 21-2. This table breaks down the object models in the RAS SDK and their associated controllers. As you begin to work with RAS you ll soon discover the relationship between each as you modify reports at run time get an existing value from the object model make some changes to it then pass it to a .
