B0749SL7NW EBOK by Unknown

Author:Unknown
Language: eng
Format: azw3
Publisher: UNKNOWN
Published: 0101-01-01T00:00:00+00:00

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Figure 3.2 The architecture of a typical client/server application Tier 1, the client tier, comprises the UI; tier 2, the server tier, comprises the business objects of the application; tier 3, the persistent data tier, comprises data storage components such as data files and database tables. In the case of the themed application, the third tier comprises a data file that stores an array of members of the Media Store. In a typical client/server application, the UI interacts with the server-side objects which, in turn, interact with the data tier. In other words, the UI interacts with the server-tier; the UI does not access the data tier directly.

The double-headed arrow (in the figure) that implies that the client and server tiers are connected is, in the case of a standalone application, an indication that the client and server tiers are deployed in the same address space. In the case of a networked application, the connection between the client and server tiers will either be an intranet or the Internet.

Now that we have placed user interfaces in the context of a client/server architecture, the next section moves on to find out how a UI is constructed.

3.3 The Construction of User Interfaces

In broad terms, there are two principal stages in the construction of a UI.

1. Organising UI components;

2. Activating UI components. Stage 1 involves organising the layout and relative positions of UI components such as buttons, text fields and so on; stage 2 involves activating those components that are designed to call methods implemented in server-side classes in response to the user ‘operating’ the component.

3.3.1 Organising User Interface Components: Some Examples

The principal task associated with graphical user interface (GUI) design involves making decisions about organising UI components (also known as controls) into what are known as containers. • A container is an object that can contain components and other containers;

• a component is an object that is (usually) visible when the GUI is displayed;

• a layout manager is an object that is used to organise the position of components in their container.

The aim of the examples that follow is to illustrate a structured approach to GUI design. At the end of the set of examples, we will be in a good position to make a number of points about classes used to organise and contain components.

Example One

Figure 3.3 shown a simple GUI; its code is shown on the next page. The reader should read the comments in the code in order to get an initial understanding about how the GUI is created.

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