我有一个问题,在使用插值滚动值时,我无法将图像的初始不透明度设置为0。
因此,当我使用logoOpacity
值Animated.View是完全可见的,但是例如,如果我使用__opacity
它确实应用有效值,图像部分可见。
使用logoOpacity
变量在我开始滚动时正确工作 - 这是关于初始值的全部 - 我无法设置隐藏视图。
如何在滚动时进行插值并启动Animated.View从0到100的可见性?
请参阅以下代码:
import React, { Component } from 'react';
import {
Animated,
Platform,
} from 'react-native';
import {connectStyle} from "@shoutem/theme/index";
import { View } from '@shoutem/ui/components/View'
import { Text } from '@shoutem/ui/components/Text'
import { Image } from '@shoutem/ui/components/Image'
import { Fonts, Colors, Layout } from '../../constants';
const HEADER_MAX_HEIGHT = 260; //
const HEADER_MIN_HEIGHT = 160; // Layout.NAVIGATION_HEADER_HEIGHT; // Platform.OS === 'ios' ? 60 : 73;
const HEADER_SCROLL_DISTANCE = HEADER_MAX_HEIGHT - HEADER_MIN_HEIGHT;
/**
* https://medium.com/appandflow/react-native-scrollview-animated-header-10a18cb9469e
*
*/
class OpportunityBlock extends Component {
constructor(props) {
super(props);
this.state = {
scrollY: new Animated.Value(
// iOS has negative initial scroll value because content inset...
Platform.OS === 'ios' ? -HEADER_MAX_HEIGHT : 0,
)
};
}
render() {
const { style } = this.props
// Because of content inset the scroll value will be negative on iOS so bring
// it back to 0.
const scrollY = Animated.add(
this.state.scrollY,
Platform.OS === 'ios' ? HEADER_MAX_HEIGHT : 0,
);
// Small logo animations
const logoOpacity = scrollY.interpolate({
inputRange: [0, HEADER_SCROLL_DISTANCE / 2, HEADER_SCROLL_DISTANCE],
outputRange: [0, 0, 1],
extrapolate: 'clamp',
});
const __opacity = new Animated.Value(0.3);
return (
<View styleName={"vertical"}>
{/* MAIN CONTENT SECTION **/}
<Animated.ScrollView
style={{ flex: 1 }}
scrollEventThrottle={1}
onScroll={Animated.event(
[{
nativeEvent: {
contentOffset: { y: this.state.scrollY }
}
}],
{ useNativeDriver: true },
)}
>
<View style={style.scrollViewContent}>
<Text>XX</Text>
</View>
</Animated.ScrollView>
<Animated.View
style={[
style.logoContainer,
{
opacity: logoOpacity,
},
]}
>
<Image
styleName={'small'}
source={{ uri: item.images[0].url }}
/>
</Animated.View>
</View>
);
}
}
const style = {
content: {
flex: 1,
},
logoContainer: {
position: 'absolute',
top: 0,
left:0,
opacity:0,
// right: -100, // initial position
marginTop:30,
paddingLeft:10,
},
scrollViewContent: {
// iOS uses content inset, which acts like padding.
paddingTop: Platform.OS !== 'ios' ? HEADER_MAX_HEIGHT : 0 // paddingTop: HEADER_MAX_HEIGHT // Platform.OS !== 'ios' ? HEADER_MAX_HEIGHT : 0,
}
}
// connect the component to the theme
export default connectStyle('mbm.common.OpportunityBlock', style)(OpportunityBlock);
测试用例:似乎问题与scrollY动画值有关,因为那种情况不能正常工作,图像完全可见,即使是难度的scrollY也是0.也许有一些内在的滚动值?
const logoOpacityDoesNotWork = scrollY.interpolate({
inputRange: [0, 0, 250],
outputRange: [0.1, 0.1, 1],
extrapolate: 'clamp',
});
const logoOpacityWorks = (new Animated.Value(120)).interpolate({
inputRange: [0, 0, 250],
outputRange: [0.1, 0.1, 1],
extrapolate: 'clamp',
});
尝试使用0.01作为初始值。有一个错误会将0变为null,这将导致忽略不透明度值。