微信小程序文字段落展开收起组件

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实现原理：

  1. 计算每行高度
  2. 文字段落总高度除以每行高度得出总共多少行可以显示完成
  3. js设置初始显示的高度（行数*每行高度=初始高度）

引用方法：

1
<spread-text out-class="movie-review" show-num="6" text="{{detail.movie_review}}"></spread-text>

源码：

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// spread-text.json
{
  "component": true
}

// spread-text.wxml
<view class="box">
  <view id="J-text" class="component spread-text out-class" style="{{textStyle}}">
    {{text}}
  </view>
  <view class="toggle" id="J-toggle" catchtap="toggleHandler" style="display: {{showToggle}}">
    <image class="arrow {{toggleText}}" src="../../images/arrow.png"></image>
  </view>
  <view id="J-placeholder" class="out-class" style="display: {{showPlaceholder}};">测试</view>
</view>

// spread-text.wxss
:host {
  font-size: 30rpx;
  color: #333;
}

.box {
  position: relative;
}

.spread-text {
  opacity: 0;
  height: auto;
  word-wrap: break-word;
  transition: all 100ms linear 0s;
}

.toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  height: 46rpx;
}

.toggle image {
  width: 22rpx;
  height: 14rpx;
}

.toggle .arrow.up {
  transform: rotateZ(180deg);
}

// spread-text.js
Component({
  externalClasses: ['out-class'],
  properties: {
    text: String,
    showNum: {
      type: Number,
      value: 3
    }
  },
  data: {
    showPlaceholder: 'block',
    textStyle: '',
    toggleText: 'down',
    showToggle: 'none'
  },
  methods: {
    toggleHandler() {
      if (this.data.toggleText === 'down') {
        this.setData({
          toggleText: 'up',
          textStyle: `height: ${
            this.textHeight
          }px; opacity: 1; overflow: hidden;`
        });
      } else {
        this.setData({
          toggleText: 'down',
          textStyle: `height: ${this.showH}px; opacity: 1; overflow: hidden;`
        });
      }
    }
  },
  ready() {
    const query = wx.createSelectorQuery().in(this);

    query.select('#J-text').boundingClientRect();
    query.select('#J-placeholder').boundingClientRect();

    query.exec(res => {
      const textElement = res[0];
      const placeholderEelement = res[1];

      const textHeight = textElement.height;
      const placeholderHeight = parseInt(placeholderEelement.height, 10);

      this.showH = placeholderHeight * this.data.showNum;
      this.textHeight = textHeight;

      if (this.showH < textHeight) {
        this.setData({
          showToggle: 'flex',
          showPlaceholder: 'none',
          textStyle: `height: ${this.showH}px; opacity: 1; overflow: hidden;`
        });
      } else {
        this.setData({
          showToggle: 'none',
          showPlaceholder: 'none',
          textStyle: `height: ${
            this.textHeight
          }px; opacity: 1; overflow: hidden;`
        });
      }
    });
  }
});