Develop Reference

Android 7 React Native number of components limit?

I've been making my first React Native app, for now without redux, just RN. The case is on Android 7 it doesn't show a lot of components, but it does on more recent versions of Android and works perfectly on iOs.
Here are screenshots of my problem, on Android you can see a lot of blank space, but on iOs it is filled with data:
Android 7:
iOS:
Here is the structure and CSS:
<ScrollView contentContainerStyle={mainView}>
<View style={sectionStyle}>...</View>
<View style={sectionStyle}>...</View>
...
<View style={sectionStyle}>...</View>
</ScrollView>
mainView: {
backgroundColor: colors.backgroundGray,
justifyContent: 'flex-start'
},
sectionStyle: {
paddingTop: 15,
paddingBottom: 15,
backgroundColor: colors.mainWhite,
margin: 5,
borderWidth: 1,
borderColor: colors.borderGray,
borderRadius: 5,
shadowOpacity: 0.5,
shadowRadius: 2,
shadowOffset: {
width: 0,
height: 2
},
shadowColor: colors.shadowColor,
elevation: 5
}
What may cause that issue and what can be done to fix this?
UPD:
After a few days of debugging i found that problem may be caused by Android 7 limitations of number of components rendered on screen, because there are a lot of them on that page, like 10-15 screens at least with icons, comments, sliders and dropdowns. If i render just dummy text instead of them - everything is rendered, and so does if i render almost all of them by exception of, for example, dropdowns.
Any ideas?

Well once again i'm answering my own question, it feels like a meditative monolgue service :D
I've solved this problem. That page has really huge amount of complex components on it, like ~30 complex Views grouped by other Views (this is because that part of a page should be same for all products so it's hardcoded) + massive FlatList of same structured Views (this is because products have their unique structure, so it's dynamic), and all of it is inside of a ScrollView to enable scrolling (otherwise it makes no sense to have 20+ screens long page without ability to scroll it).
So i put those static hardcoded components into array, merged with dynamic components array, and rendered only one FlatList, replacing the whole ScrollView with it.

ToolbarAndroid navIcon not displaying

I'm trying to display a ToolbarAndroid with a hamburger icon. I'musing the code:
_buildToolbar (msg) {
const navIcon = require("../../icons/menu.png");
return (
<ToolbarAndroid
title={msg}
style={{
height: 56,
alignSelf: "stretch",
}}
onIconClicked={this.props.openDrawer}
navIcon={navIcon}
/>);
}
The toolbar displays, but the nav icon doesn't. I get the warning Failed prop type: Invalid prop navIcon supplied to ToolbarAndroid. The file does exist, and looking under a debugger navIcon is defined. Looking for any help here. Using an Icon based toolbar is probably not a workable solution, as due to some of our customization features getting the right font would become difficult.
Edit:
Changing to:
<ToolbarAndroid
title={msg}
style={{
height: 56,
alignSelf: "stretch",
}}
onIconClicked={this.props.openDrawer}
navIcon={
{ uri: navIcon }}
/>);
Got rid of the warning but did not fix the display issue.
Edit2:
It looks like something with our build system here (which uses the same stack as our web build system, not the normal RN tools) is loading the files as a different data type- its loading them as data uris. I'm not sure what they normally are. But when the ToolbarAndroid is passed a uri, it assumes it will be a file, an http/https url, or a name of a drawable in our drawable folder. So it looks like we're going to need to debug our build system, or hard code this image (which being a hamburger icon isn't the end of the world).

The navIcon format seems to be specific:
Action Bar icons should be 32-bit PNGs with an alpha channel for transparency. The finished action bar icon dimensions, corresponding to a given generalized screen density, are shown in the table below.
18 x 18 px
24 x 24 px
36 x 36 px
48 x 48 px
https://developer.android.com/guide/practices/ui_guidelines/icon_design_action_bar
Also you can use Icon.ToolbarAndroid from react-native-vector-icons :
https://github.com/oblador/react-native-vector-icons

This (ES6) code works on my app:
import navIcon from '../Images/navIcon.png'
...
<ToolbarAndroid
title={'test'}
style={{
height: 56,
alignSelf: 'stretch',
}}
onIconClicked={this.props.openDrawer}
navIcon={navIcon}
/>
The navIcon file:

react native fontSize limit

I was wondering if anyone had any experience with fontSize limit in react-native?
Let's say we have a Text component that renders a huge 'A' character:
<Text style={{ fontSize: 273, borderWidth: 1, borderColor: 'red' }}>A</Text>
When one changes the fontSize style to 274 or more, the character A vanishes, even though red border still remains.
This only happens on Android, iOS renders hugh font sizes as expected.
Has anyone had similar problems? Any ideas on how to proceed in order to support higher fontSize is very much appretiated.

I also experienced such a problemon my Genymotion android emulator, but the problem doesn't exist on real devices.

How can I render the ♦ (Unicode Black Diamond Suit) the same on all devices?

I need to render the Black Diamond Suit (♦, U+2666) the same on multiple browsers. Unfortunately, this is an emoji as well, meaning it renders like this:
Source
when I want it to always render like the "browser" image (top left).
This is especially frustrating on iOS and Android because it's not rendered as black.
Unfortunately, Font Awesome doesn't include a usable replacement. The nearest is "Black lozenge", U+29EB ⧫︎ but it's a bit stretched.
Is there a way to force the mobile browser to render it like a desktop browser would?

Looking at the spec found on fileformat.info there is a text version of the black diamond that can be used instead:"\u{2666}\u{FE0E}"

Use this in css
color: transparent;
text-shadow: 0 0 0 black;

2023 observation: "\u{2666}\u{FE0E}" doesn't seem to work on my Android Chrome - displays red diamond.
"\u{25C6}" does work here - black diamond is displayed on phone.
HTML code ◆

What is the default unit of style in React Native?

I am contributing to an Open Source Project where I am developing Material design for React Native. I am blocked at work,I am unable to make some UI level enhancements w.r.t. padding, alignment etc.,
This is the Official Spec of Material Design for Drawer-
In the above image, the UNIT of measurement is dp.
But, in my React Native code, I see there is no such units mentioned. Considering it is "react native" I am confused whether it is px or dp.
I even went over the Official Docs of React Native for Style component. I don't see a mention anywhere.
My Code looks like-
const styles = {
touchable: {
paddingHorizontal: 16,
marginVertical: 8,
height: 48
},
item: {
flex: 1,
flexDirection: 'row',
alignItems: 'center',
},
icon: {
position: 'relative',
},
value: {
flex: 1,
paddingLeft: 34,
top: 2
},
label: {
top: 2
}
},
Please can you tell me, if this is pixels or dp? And also, is 1px = 1dp?

From the docs:
All dimensions in React Native are unitless, and represent
density-independent pixels. Setting dimensions this way is common for components that should always render at exactly the same size, regardless of screen dimensions.
So yes, units in React Native are in dp. If you want to convert them to pixels, use PixelRatio.getPixelSizeForLayoutSize()

I share your confusion somewhat, not being able to actively inspect with a developer console as we are used to in the browser.
I am not familiar with the 'dp' unit, but from what I gather width: 1 renders differently on each device depending on the pixel density of the screen (see link). The information in the react-native docs say that 1 would render thicker on screens with high pixel density. Which then sounds logical as you have more precision on high density screens than you would have on low density screens and react-native aims at being universal so it would not assume high dpi.
It is my understanding that you can use the below linked PixelRatio API to calculate sizes for detail elements (think borders, icons, etc), that way you can dynamically adjust the rendered size according to the device's screen density.
https://facebook.github.io/react-native/docs/pixelratio.html#content

It is the pixel ratio that you have to consider. pixel represents an absolute value. pixel ratio is a relative value. to make app screen and components responsive you have to use pixel ratio.
i have been using in multiple apps already. and i think that is how you have to do it. hope this answers your question.

From what I know, the javascript styling that we use in react js or react native uses pixels. Pixel ratio is only needed to support different size of mobile device screens.