React-Native组件ImageBackground-蒲公英云

React-Native组件ImageBackground

Dear 丶 2022-05-30 04:53 339阅读 0赞

1.基础知识

在RN版本0.46版本的时候添加了ImageBackground控件，在0.46版本以后使用Image的时候不能在嵌套使用，ImageBackground就是解决这个问题的，现在如果在标签中嵌套其他组件现在会报黄盒警告。ImageBackground的使用和Image一样，只不过可以嵌套其他组件了。

在 “react-native”: “0.54.0”,中，直接会出现红屏，使用的方式如下所示：

<ImageBackground
      style={
   {height:100,width:300}} 
      resizeMode='cover'
     >
         <Text style={
   {color:'red',fontSize:24}}> image 嵌入 text</Text>
</ImageBackground>

下面是具体的实现代码：

/**
 * Copyright (c) 2015-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @providesModule ImageBackground
 * @flow
 * @format
 */
'use strict';
const Image = require('Image');
const React = require('React');
const StyleSheet = require('StyleSheet');
const View = require('View');
const ensureComponentIsNative = require('ensureComponentIsNative');
import type {NativeMethodsMixinType} from 'ReactNativeTypes';
/**
 * Very simple drop-in replacement for <Image> which supports nesting views.
 *
 * ```ReactNativeWebPlayer
 * import React, { Component } from 'react';
 * import { AppRegistry, View, ImageBackground, Text } from 'react-native';
 *
 * class DisplayAnImageBackground extends Component {
 *   render() {
 *     return (
 *       <ImageBackground
 *         style={
   {width: 50, height: 50}}
 *         source={
   {uri: 'https://facebook.github.io/react-native/img/opengraph.png'}}
 *       >
 *         <Text>React</Text>
 *       </ImageBackground>
 *     );
 *   }
 * }
 *
 * // App registration and rendering
 * AppRegistry.registerComponent('DisplayAnImageBackground', () => DisplayAnImageBackground);
 * ```
 */
class ImageBackground extends React.Component<$FlowFixMeProps> {
  setNativeProps(props: Object) {
    // Work-around flow
    const viewRef = this._viewRef;
    if (viewRef) {
      ensureComponentIsNative(viewRef);
      viewRef.setNativeProps(props);
    }
  }
  _viewRef: ?NativeMethodsMixinType = null;
  _captureRef = ref => {
    this._viewRef = ref;
  };
  render() {
    const {children, style, imageStyle, imageRef, ...props} = this.props;
    return (
      <View style={style} ref={this._captureRef}>
        <Image
          {...props}
          style={[
            StyleSheet.absoluteFill,
            {
              // Temporary Workaround:
              // Current (imperfect yet) implementation of <Image> overwrites width and height styles
              // (which is not quite correct), and these styles conflict with explicitly set styles
              // of <ImageBackground> and with our internal layout model here.
              // So, we have to proxy/reapply these styles explicitly for actual <Image> component.
              // This workaround should be removed after implementing proper support of
              // intrinsic content size of the <Image>.
              width: style.width,
              height: style.height,
            },
            imageStyle,
          ]}
          ref={imageRef}
        />
        {children}
      </View>
    );
  }
}
module.exports = ImageBackground;

从代码可以看出，只是仅仅对 Image 进行了View的包装而已，并且能够看到将包含在ImageBackground 中的 children 使用Image进行了包装，给外层抛出一下三个接口： style, imageStyle, imageRef，从官网能够得知，唯一的不同就是名字的不同，属性与用法完全和Image一致。

官网说明如下链接：
1.react-native中背景图片属性ImageBackground
2.react-native中背景图片属性ImageBackground-中文网

2.实例操作

如何将背景图片修饰为圆形，并且在里边输入文字

<ImageBackground source={imageSrc} style={ { justifyContent: 'center', alignItems: 'center', width: 60, height: 60, resizeMode: 'cover', borderRadius: 60 / 2, cursor: 'pointer', overflow: 'hidden', borderWidth: 0, borderColor: 'rgba(200,200,200,0.5)' }} > <Text>{'客'}</Text> </ImageBackground>

如上所示代码，通过宽高进行控制一个正方形，然后再通不过属性borderRadius进行控制圆角，由于是直径的一半，所以最终构造成圆形，在这个时候会出现在ios系统中仍然是一个正方形，需要使用属性overflow: 'hidden', 来控制最终圆角的形成，ios中默认给控件加圆角时圆角之外的图案是还在的，在react-native中需要设置css的一个样式 overflow：hidden属性，最终实现效果如下图所示：

圆形图片效果图