Conditional Rendering
In React, you can create distinct components that encapsulate behavior you need. Then, you can render only some of them, depending on the state of your application.
Conditional rendering in React works the same way conditions work in JavaScript. Use JavaScript operators like if or the conditional operator to create elements representing the current state, and let React update the UI to match them.
Consider these two components:
We’ll create a Greeting component that displays either of these components depending on whether a user is logged in:FinRL 入门指南
This example renders a different greeting depending on the value of isLoggedIn prop.
You can use variables to store elements. This can help you conditionally render a part of the component while the rest of FinRL 入门指南 the output doesn’t change.
Consider these two new components representing Logout and Login buttons:
In the example below, we will create a stateful component called LoginControl .
It will render either or depending on its current state. It will also render a from the previous example:
While declaring a variable and using an if statement is a fine way to conditionally render a component, sometimes you might want to use a shorter syntax. There FinRL 入门指南 are a few ways to inline conditions in JSX, explained below.
Inline If with Logical && Operator
You FinRL 入门指南 may embed any expressions in JSX by wrapping them in curly braces. This includes the JavaScript logical && operator. It can be handy for conditionally including an element:
It works because in JavaScript, true && FinRL 入门指南 expression always evaluates to expression , and false && expression always evaluates to false .
Therefore, if the condition is FinRL 入门指南 true , the element right after && will appear in the output. If it is false , React will ignore and skip it.
Inline If-Else with Conditional Operator
Another method for conditionally rendering elements inline is to use the FinRL 入门指南 JavaScript conditional operator condition ? true : false .
In the example below, we use it to conditionally render a small block of text.
It can also be used for larger expressions although it is less obvious what’s FinRL 入门指南 going on:
Just like in JavaScript, it is up to you to choose an appropriate style based on FinRL 入门指南 what you and your team consider more readable. Also remember that whenever conditions become too complex, it might be a good time to extract a component.
Preventing Component from Rendering
In rare cases you might want a component to hide itself even though it was rendered by another component. To do this return null instead of its render output.
In the example below, the is rendered depending on the value of the prop called warn . If the value of the prop is false , then the component does not render:
Returning null from a component’s render method does not affect the firing of the component’s lifecycle methods. For instance componentDidUpdate will still be called.
FinRL 入门指南
Viaggio fotografico (1): Arrivo a Reykjavik
App Eachine TEC: risolvere il crash col drone e520s
Scegliere il primo drone fotografico
Fotografare stelle e costellazioni puntiformi
FinRL 入门指南 Quando comincia la notte per l'astrofotografo?
Luna: stacking con Autostakkert! 3
L'uso dei filtri LRGB in astrofotografia
2020: Benvenuto Clicks from Sicily
Filtro Hutech IDAS LPS-D1, prime impressioni
About FinRL 入门指南
Mi chiamo Sebastiano, vivo in Sicilia orientale e sono una guida turistica di professione con una profonda predilezione per le escursioni archeologiche in siti minori. Da tanti anni, quando e come posso mi occupo di fotografia. La mia passione per la fotografia nasce all' "epoca della pellicola", affiancandosi a quella per l'astronomia e portandomi giovanissimo a sperimentare le prime riprese della volta celeste con le pellicole più sensibili che riuscissi a trovare nei negozi e usando la motorizzazione del mio piccolo telescopio. In seguito l'interesse per la FinRL 入门指南 fotografia si è ampliando, sconfinando dalla nicchia specialistica dell'astrofotografia. Attualmente amo molto anche la fotografia di paesaggio, la travel photography e ho accomunato gli interessi professionali per i monumenti e i siti archeologici siciliani all'amore per la fotografia, cominciando un progetto - senza data di scadenza - di documentazione di luoghi, FinRL 入门指南 siti e monumenti dell'isola. In quasi quindici anni di attività e innumerevoli escursioni esplorative è facile immaginare che l'archivio fotografico sia cresciuto a dismisura e, nei ritagli di tempo, cerco di condividere la documentazione dei luoghi più belli della Sicilia andando ad aggiungere nuove gallerie fotografiche a questo sito. Dimenticavo! Anche il sito internet esiste ormai da numerosi anni ma ha recentemente cambiato nome. Per tanti anni il mio sito internet era chiamato "Sicilystockphoto" ma maturando obiettivi e interessi diversi nel 2020 ho deciso di dargli una rinfrescata FinRL 入门指南 nella graffica e nel nome. Come spesso capita gli interessi fotografici vanno cambiando nel tempo. Attualmente sono di nuovo molto impegnato nell'astrofotografia e per tale motivo sia tra gli articoli nel blog che tra le foto, è possibile trovare ampio spazio per questo particolare e specialissimo settore della fotografia. Potete trovare piccoli articoli da me scritti su quanto ho appreso e sui miei progetti fotografici nella sezione blog.
Per maggiori FinRL 入门指南 FinRL 入门指南 informazioni sull'attrezzatura utilizzata per realizzare le fotografie pubblicate su questo sito potete dare un'occhiata alla pagina:
Per quanto riguarda l'astrofotografia trovate dettagli sul mio attuale setup alla pagina
Se invece doveste essere interessati ai miei servizi professionali come guida turistica, potete visitare il sito:
Composition vs Inheritance
React has a powerful composition model, FinRL 入门指南 and we recommend using composition instead of inheritance to reuse code between components.
In this section, we will consider a few problems where developers new to React often reach for inheritance, and show how we FinRL 入门指南 can solve them with composition.
Some components don’t know their children ahead of time. This is especially common for components like Sidebar or Dialog that represent generic “boxes”.
We recommend that such components use the special children prop to pass children elements directly into their output:
This lets other components pass arbitrary children to them by nesting the JSX:
Anything inside the JSX tag gets passed into the FancyBorder component as a children prop. Since FancyBorder renders inside a , the passed elements appear in the final output.
While this is less common, sometimes you might need multiple “holes” in a component. In such cases you may come up with your own convention instead of using children :
React elements like and are just objects, so you can pass them as props like any other data. This approach may remind you of “slots” in other FinRL 入门指南 libraries but there are no limitations on what you can pass as props in React.
Sometimes we think FinRL 入门指南 about components as being “special cases” of other components. For example, we might say that a WelcomeDialog is a special case of Dialog .
In React, this is also achieved by composition, where a more “specific” component renders a more “generic” one and configures it with props:
Composition works equally well for components defined FinRL 入门指南 as classes:
So What About Inheritance?
At Facebook, we use React in thousands of components, and we haven’t FinRL 入门指南 found any use cases where we would recommend creating component inheritance hierarchies.
Props and composition give you all the flexibility you need to customize a component’s look and behavior in an explicit and safe way. Remember that components may accept arbitrary props, including primitive values, React elements, or functions.
If you want to reuse non-UI functionality between components, we suggest extracting it into a separate JavaScript module. The components may import it and use that function, object, or a class, without extending it.
FinRL 入门指南
Information on the service provider according to Section 5 TMG (German Telemedia Law)
1NCE GmbH
Sternengasse 14-16
50676 Cologne
Germany
(hereinafter FinRL 入门指南 FinRL 入门指南 also referred to as the “Supplier” or “we”)
Register entry
Entry in the Commercial Register.
Register court: Cologne Local Court
Register number: HRB 92529
Sales tax
Sales tax identification number according to Section 27a of the German Sales Tax Law:
DE 315 149 474
Supervising authority
Bundesnetzagentur für Elektrizität, Gas, Telekommunikation, Post und Eisenbahnen
Tulpenfeld 4
53113 Bonn
Dispute settlement
We are not obliged to participate in a dispute settlement procedure before a consumer conciliation body and cannot offer you such a procedure.The European Commission’s platform for online dispute resolution can be found online at http://ec.europa.eu/consumers/odr/.
Objection to advertising
The use of our contact data to send unsolicited advertising and information material is hereby rejected. We expressly reserve the right to take legal action in the case of the unsolicited sending of advertising information.
Liability for contents
As a service provider, we are responsible for our own content on these pages in accordance with Section 7 Paragraph 1 TMG (German Telemedia Act) in accordance with the general laws. According to Sections 8 to 10 TMG, however, we as FinRL 入门指南 a service provider are not obliged to monitor transmitted or stored third-party information or to investigate circumstances FinRL 入门指南 that indicate illegal activity. Obligations to remove or block the use of information in accordance with general laws FinRL 入门指南 remain unaffected by this. However, liability in this regard is only possible from the time of knowledge of FinRL 入门指南 a concrete violation of the law. If we become aware of any such violations of the law, we FinRL 入门指南 will remove these contents immediately.
Liability for links
Our website may contain links to external third-party websites over FinRL 入门指南 whose contents we have no influence. We accept no liability for these external contents and expressly disassociate ourselves from them. The respective provider of the pages is responsible for the contents of the linked pages. The FinRL 入门指南 linked pages were checked for obvious legal infringements at the time of linking. Clearly illegal contents were not recognizable at the time of linking. However, constant checking of the contents of the linked pages is FinRL 入门指南 unreasonable without concrete evidence of a violation of the law. We will remove such links as soon as FinRL 入门指南 we become aware of any infringements of the law.
Copyright
The contents provided by us on these pages (texts, graphics, logos, images, etc.) are subject to copyright protection. Reproduction, processing, distribution and any other use outside the limits of copyright law require the prior written consent of the respective author. Downloads and copies of the contents are only permitted for private use and not for commercial use.
Mandatory disclosures under telecommunications law
Information on all the procedures installed by 1NCE to measure and control data traffic in order to avoid full load or overload of network connections and information on the potential effects of such procedures on FinRL 入门指南 FinRL 入门指南 service quality as well as information on the nature of measures installed to ensure that 1NCE reacts adequately to security and integrity incidents and to threats and weaknesses in the systems is available for download here.
Photo credits
Water meter: deepblue4you / istockphoto.com
Dumpster: teptong / thinkstockphotos.de
Fork lifter: Bet_Noire / thinkstockphotos.de