React Native persist data. Saving and reading data from AsyncStorage


In previous post: React Native editable list I showed, how to edit data of single element on list. The edited data was saved to the component state, which allowed it to be displayed on the screen. However, when you close the application, the data resets and are not saved. How to change that? AsyncStorage will help.

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How to pass data from child component to parent component in React Native?


How to update parent state from child component in React Native ?

Passing data from child component to parent component is easy. When we place child component in parent’s content we must use function (sets in parent component and invoked in child component), which sets data in the parent’s component state, when action is made in child’s component, e.g. by clicking the button. The diagram is as follows:

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ScrollView performance improved – react native scrollview infinite scroll


Jak wiemy z dokumentacji React Native, ScrollView renderuje wszystkie swoje dzieci na raz, co przy dużej ich ilości może powodować problemy z wydajnością. Istnieje jednak sposób, by rozłożyć renderowanie dużej ilości danych w czasie tak, aby użytkownik nie odczuł tych problemów. Możemy wyświetlić przykładowo 20 elementów przy pierwszym wczytaniu danych i dodawać kolejno nowe elementy w miarę przewijania listy. Tak stworzymy “niekończące się” przewijanie, tzw. “infnite scroll”.

As we know from React Native documentation, ScrollView renders all of its children at once, which can cause performance problems with a large number of them. However, there is a way to spread in time rendering of large number of data, so that the user does not feel these problems. For example, we can display 20 items at the first time when load data and add new items one by one while scrolling the list. That’s how we’ll create “endless” scrolling, so-called “infnite scroll”.

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How to set button width and height in React Native?


It often happens that we want to change the dimensions of the button, which by default is extended to the entire width of the parent element. While reducing its width is not a problem – it is enough to reduce the width of the parent, but changing the height is already problematic. The Button element has no style property, so apart from changing the text color on iOS and the background color on Android, we can not set much in it.

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