--- title: Building the UI order: 2 layout: page --- [[application.architecture]] = Building the UI Vaadin Framework user interfaces are built hierarchically from components, so that the leaf components are contained within layout components and other component containers. Building the hierarchy starts from the top (or bottom - whichever way you like to think about it), from the [classname]#UI# class of the application. You normally set a layout component as the content of the UI and fill it with other components. [source, java] ---- public class MyHierarchicalUI extends UI { @Override protected void init(VaadinRequest request) { // The root of the component hierarchy VerticalLayout content = new VerticalLayout(); content.setSizeFull(); // Use entire window setContent(content); // Attach to the UI // Add some component content.addComponent(new Label("Hello! - How are you?", ContentMode.HTML)); Grid grid = new Grid<>(); grid.setCaption("My Grid"); grid.setItems(GridExample.generateContent()); grid.setSizeFull(); content.addComponent(grid); content.setExpandRatio(grid, 1); // Expand to fill } } ---- The component hierarchy is illustrated in <>. [[figure.application.architecture.schematic]] .Schematic diagram of the UI image::img/ui-schematic.png[width=80%, scaledwidth=100%] The actual UI is shown in <>. [[figure.application.architecture.example]] .Simple hierarchical UI image::img/ui-architecture-hierarchical.png[width=70%, scaledwidth=90%] Instead of building the layout in Java, you can also use a declarative design, as described later in <>. The examples given for the declarative layouts give exactly the same UI layout as built from the components above. The easiest way to create declarative designs is to use Vaadin Designer. The built-in components are described in <<../components/components-overview.asciidoc#components.overview,"User Interface Components">> and the layout components in <<../layout/layout-overview.asciidoc#layout.overview,"Managing Layout">>. The example application described above just is, it does not do anything. User interaction is handled with event listeners, as described a bit later in <>. [[application.architecture.architecture]] == Application Architecture Once your application grows beyond a dozen or so lines, which is usually quite soon, you need to start considering the application architecture more closely. You are free to use any object-oriented techniques available in Java to organize your code in methods, classes, packages, and libraries. An architecture defines how these modules communicate together and what sort of dependencies they have between them. It also defines the scope of the application. The scope of this book, however, only gives a possibility to mention some of the most common architectural patterns in Vaadin applications. The subsequent sections describe some basic application patterns. For more information about common architectures, see <<../advanced/advanced-architecture#advanced.architecture,"Advanced Application Architectures">>, which discusses layered architectures, the Model-View-Presenter (MVP) pattern, and so forth. [[application.architecture.composition]] == Compositing Components User interfaces typically contain many user interface components in a layout hierarchy. Vaadin provides many layout components for laying contained components vertically, horizontally, in a grid, and in many other ways. You can extend layout components to create composite components. [source, java] ---- class MyView extends VerticalLayout { TextField entry = new TextField("Enter this"); Label display = new Label("See this"); Button click = new Button("Click This"); public MyView() { addComponent(entry); addComponent(display); addComponent(click); setSizeFull(); addStyleName("myview"); } } // Create an instance of MyView Layout myview = new MyView(); ---- While extending layouts is an easy way to make component composition, it is a good practice to encapsulate implementation details, such as the exact layout component used. Otherwise, the users of such a composite could begin to rely on such implementation details, which would make changes harder. For this purpose, Vaadin has the special wrappers [classname]#Composite# and [classname]#CustomComponent#, which hide the content representation. [source, java] ---- class MyView extends CustomComponent { TextField entry = new TextField("Enter this"); Label display = new Label("See this"); Button click = new Button("Click This"); public MyView() { Layout layout = new VerticalLayout(); layout.addComponent(entry); layout.addComponent(display); layout.addComponent(click); setCompositionRoot(layout); setSizeFull(); } } // Create an instance of MyView MyView myview = new MyView(); ---- For a more detailed description of [classname]#Composite# and [classname]#CustomComponent#, see <<../components/components-customcomponent#components.customcomponent,"Composition with Composite and CustomComponent">>. [[application.architecture.navigation]] == View Navigation While the simplest applications have just one __view__ (or __screen__), most of them often require several. Even in a single view, you often want to have sub-views, for example to display different content. <> illustrates a typical navigation between different top-level views of an application, and a main view with sub-views. [[figure.application.architecture.navigation]] .Navigation Between Views image::img/view-navigation-hi.png[width=80%, scaledwidth=100%] The [classname]#Navigator# described in <<../advanced/advanced-navigator#advanced.navigator,"Navigating in an Application">> is a view manager that provides a flexible way to navigate between views and sub-views, while managing the URI fragment in the page URL to allow bookmarking, linking, and going back in the browser history. Often Vaadin application views are part of something bigger. In such cases, you may need to integrate the Vaadin applications with the other website. You can use the embedding techniques described in <<../advanced/advanced-embedding#advanced.embedding,"Embedding UIs in Web Pages">>. [[application.architecture.accessing]] == Accessing UI, Page, Session, and Service You can get the UI and the page to which a component is attached to with [methodname]#getUI()# and [methodname]#getPage()#. However, the values are [literal]#++null++# until the component is attached to the UI, and typically, when you need it in constructors, it is not. It is therefore preferable to access the current UI, page, session, and service objects from anywhere in the application using the static [methodname]#getCurrent()# methods in the respective [classname]#UI#, [classname]#Page#, [classname]#VaadinSession#, and [classname]#VaadinService# classes. [source, java] ---- // Set the default locale of the UI UI.getCurrent().setLocale(new Locale("en")); // Set the page title (window or tab caption) Page.getCurrent().setTitle("My Page"); // Set a session attribute VaadinSession.getCurrent().setAttribute("myattrib", "hello"); // Access the HTTP service parameters File baseDir = VaadinService.getCurrent().getBaseDirectory(); ---- You can get the page and the session also from a [classname]#UI# with [methodname]#getPage()# and [methodname]#getSession()# and the service from [classname]#VaadinSession# with [methodname]#getService()#. The static methods use the built-in ThreadLocal support in the classes. ifdef::web[] The pattern is described in <<../advanced/advanced-global#advanced.global.threadlocal,"ThreadLocal Pattern">>. endif::web[] 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494