11/14/2023 0 Comments Flutter widgetsThat previously never changed will need to change. Software tends to change a lot, and it is likely that in the future, a value Its value, there is no guarantee that tomorrow will be the same. With this assumption is that, while today that provider may indeed never update Using ref.read this way is commonly associated with the thought "The valueĮxposed by a provider never changes so using 'ref.read' is safe". The ref.listen method can be used inside the body of a provider:īut this is a very bad practice and can cause bugs that are difficult to track. The callback function when called will be passed 2 values, the value of the previous State and the value of the new State. The ref.listen method needs 2 positional arguments, the first one is the Provider and the second one is the callback function that we want to execute when the state changes. That can be useful for performing actions when a certain change happens, suchĪs showing a snackbar when an error happens. If the listened to provider changes, using ref.listen will instead call a custom function. The main difference between them is that, rather than rebuilding the widget/provider Similarly to ref.watch, it is possible to use ref.listen to observe a provider. Using ref.listen to react to a provider change In those cases, consider using ref.read instead. Inside initState and other State life-cycles. Like inside an onPressed of an ElevatedButton. In the app.The watch method should not be called asynchronously, In the test app that these images are from, I also have a list of all the dogs There's no need to re-write this widget over and over.Īnd, this circle image doesn't care at all about what it's displaying. You may want a round image of a certain size, you can just pass in a url and This component is designed for re-usability because anywhere in your app that Then, anywhere in your app, you can reuse this Widget: new CircleImage('https.). The most important part of using Flutter Widgets effectively is designing yourįor example, the CircleImage widget from the image above: class CircleImage extends StatelessWidget Such as `columns`and `padding` in here that I'm glossing over. This isn't _exactly_ accurate, there are layout widgets This is the widget hierarchy for this page: The rest are outlined white, and they're simply dumb components that have noĬoncern over their content, they just display what they're told. The blue outlines represent pieces of UI that logically group together. This picture is from one of the tutorial apps on FlutterByExample, and this isĪ detail page, of which there is one for every dog in the app. In this picture, every thing that's outlined is a widget: If you're coming from the web: imagine that your CSS, HTML, and JavaScript are all handled by A simple widget that adds a background color: const BoxDecoration(background: Colors.blue).A simple widget that a user interacts with const Button(onTap. A simple widget that displays text: const Text('Hello World').With layout, or it may handle interaction. It's widgets all the way down.įlutter is unique in that every aspect of UI is handled with Widgets.Ī widget might display something, it might help define design, it might help Even the root of yourĪpp is just a widget. Widgets are nested inside of each other to build your app. Like building a lego set - piece by piece. UI that you can combine to make a complete app.
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