需求:更改elementui中el-transfer样式， 实现单击左侧选项即加入右边选框，单击右侧选项即可回到左侧选框，中间左右来回按钮更改为左侧全选右侧全选,最终修改后效果图如下

下图源码可通过github下载：https://github.com/applebring/elementui

本以为自己能够不看elementui源码实现这需求，在折腾了一天还没实现后，还是回归到其源码进行研究，自己通过纯vue实现主要遇到了以下问题:

若是不需要进行模糊查询可通过index进行增删改查实现穿梭框功能，但是若是加入模糊查询则问题百出，但进行filter过滤器过滤后，数组index发生了变化，通过index进行增删改查行不通，当然，本人在同事指点下换了思路，通过给每个选项一个固定的识别id进行对象查找和增删改，虽然增删改查实现了，但是全选却不知如何能实现，毕竟通过计算属性得到数组，当把数组清空时，无法让对象复制到右边选框~

因此，值此星期六日之际，对elementui代码进行研究，以解心中之虑

1、首先是上github拉取elementui源码https://github.com/ElemeFE/element

2、本人在名为elementui源码文件夹下克隆github上element源码，在拉取后的element文件夹中packages文件目录下找到transfer文件夹，该文件即为el-transfer源码

3、将源码复制到自己项目中，通过组件方式将其引入,本人将main.vue复制在transfermain.vue文件夹下，将transfer-panel.vue复制在transferPanel.vue文件下，如

通过观察源代码，可以看出el-transfer实际上是将穿梭框分成两部分，左右边选择框分别为重复引入transferPanel组件，即tranfermain.vue实际上可分解为如下

因此，想要修改tranfer-panel样式可在transferPanel.vue里面更改，中间的按钮组在tansfermain.vue里更改，由上面可知，我们需要引入三个文件，内容分别如下：(以下文件为范例)

transfer.vue

<template>
<div>
<el-card class="box-card">
      <dir-transfer v-model="value2" filter-placeholder="请输入城市拼音"
    :data="data2" :titles="titles"></dir-transfer>
</el-card>
</div>
</template>
<script>
import DirTransfer from './transfermain.vue'
  export default {
    data() {
      const generateData2 = _ => {
        const data = [];
        const cities = ['上海', '北京', '广州', '深圳', '南京', '西安', '成都'];
        const pinyin = ['shanghai', 'beijing', 'guangzhou', 'shenzhen', 'nanjing', 'xian', 'chengdu'];
        cities.forEach((city, index) => {
          data.push({
            label: city,
            key: index,
            pinyin: pinyin[index]
          });
        });
        return data;
      };
      return {
        data2: generateData2(),
        value2: [],
        titles:['选择成员','选中成员'],//左右穿梭框的标题
        filterMethod(query, item) {
          return item.pinyin.indexOf(query) > -1;
        }
      };
    },
    components:{DirTransfer}
  };
</script>

在该页面dir-transfer即与el-transfer一致，属性，方法，事件均与官方文档一致

transfermain.vue(本应该为源码，本处直接粘贴更改后的代码)

<template>
  <div class="el-transfer">
    <transfer-panel
      v-bind="$props"
      ref="leftPanel"
      :filterable="true"
      :data="sourceData"
      :title="titles[0] || t('el.transfer.titles.0')"
      :default-checked="leftDefaultChecked"
      @checked-change="onSourceCheckedChange">
      <slot name="left-footer"></slot>
    </transfer-panel>
    <div class="el-transfer__buttons">
      <el-button
        type="primary"
        :class="['el-transfer__button', hasButtonTexts ? 'is-with-texts' : '']"
        @click.native="allToLeft">
        <span>左全选</span><!--此处本人更改为自己所需按钮，按钮事件名字也从addToLeft改为allToLeft-->
      </el-button>
      <el-button
        type="primary"
        :class="['el-transfer__button', hasButtonTexts ? 'is-with-texts' : '']"
        @click.native="allToRight">
        <span>右全选</span><!--此处本人更改为自己所需按钮，按钮事件名字也从addToRight改为allToRight-->
      </el-button>
    </div>
    <transfer-panel
      v-bind="$props"
      :filterable="false"
      :isRight="true"
      ref="rightPanel"
      :data="targetData"
      :title="titles[1] || t('el.transfer.titles.1')"
      :default-checked="rightDefaultChecked"
      :placeholder="filterPlaceholder || t('el.transfer.filterPlaceholder')"
      @checked-change="onTargetCheckedChange">
      <slot name="right-footer"></slot>
    </transfer-panel>
  </div>
</template>

<script>
  import ElButton from 'element-ui/packages/button';
  import Emitter from 'element-ui/src/mixins/emitter';
  import Locale from 'element-ui/src/mixins/locale';
  import TransferPanel from './transferPanel.vue';
  import Migrating from 'element-ui/src/mixins/migrating';

  export default {
    name: 'ElTransfer',

    mixins: [Emitter, Locale, Migrating],

    components: {
      TransferPanel,
      ElButton
    },

    props: {
      data: {
        type: Array,
        default() {
          return [];
        }
      },
      titles: {
        type: Array,
        default() {
          return [];
        }
      },
      buttonTexts: {
        type: Array,
        default() {
          return [];
        }
      },
      filterPlaceholder: {
        type: String,
        default: ''
      },
      filterMethod: Function,
      leftDefaultChecked: {
        type: Array,
        default() {
          return [];
        }
      },
      rightDefaultChecked: {
        type: Array,
        default() {
          return [];
        }
      },
      renderContent: Function,
      value: {
        type: Array,
        default() {
          return [];
        }
      },
      format: {
        type: Object,
        default() {
          return {};
        }
      },
      filterable: Boolean,
      props: {
        type: Object,
        default() {
          return {
            label: 'label',
            key: 'key',
            disabled: 'disabled'
          };
        }
      },
      targetOrder: {
        type: String,
        default: 'original'
      }
    },

    data() {
      return {
        leftChecked: [],
        rightChecked: [],
        checkedleft:true,
        checkedright:false
      };
    },

    computed: {
      dataObj() {
        const key = this.props.key;
        return this.data.reduce((o, cur) => (o[cur[key]] = cur) && o, {});
      },
  
      sourceData() {
        console.log("this",this.data);
        return this.data.filter(item => this.value.indexOf(item[this.props.key]) === -1);
      },

      targetData() {
        return this.targetOrder === 'original'
          ? this.data.filter(item => this.value.indexOf(item[this.props.key]) > -1)
          : this.value.map(key => this.dataObj[key]);
      },

      hasButtonTexts() {
        return this.buttonTexts.length === 2;
      }
    },

    watch: {
      value(val) {
        this.dispatch('ElFormItem', 'el.form.change', val);
      }
    },

    methods: {
      getMigratingConfig() {
        return {
          props: {
            'footer-format': 'footer-format is renamed to format.'
          }
        };
      },

      onSourceCheckedChange(val, movedKeys) {
        console.log("this leftCheck",this.leftChecked)
        this.leftChecked = val;
        if (movedKeys === undefined) return;
        this.$emit('left-check-change', val, movedKeys);
        this.addToRight();//在此处直接把选中项添加到右边框，实现单击操作，而不需通过按钮再次操作
      },

      onTargetCheckedChange(val, movedKeys) {
        this.rightChecked = val;
        if (movedKeys === undefined) return;
        this.$emit('right-check-change', val, movedKeys);
        this.addToLeft();//在此处直接把选中项添加到左边框，实现单击操作，而不需通过按钮再次操作
      },
      allToLeft(){
         this.$refs.leftPanel.handleAllCheckedChange(true);//直接出发全选事件，父组件调用子组件方法需要通过this.$refs.组件ref值.子组件方法名
      },
      addToLeft() {
        let currentValue = this.value.slice();
        this.rightChecked.forEach(item => {
          const index = currentValue.indexOf(item);
          if (index > -1) {
            currentValue.splice(index, 1);
          }
        });
        this.$emit('input', currentValue);
        this.$emit('change', currentValue, 'left', this.rightChecked);
      },
      allToRight(){
         this.$refs.rightPanel.handleAllCheckedChange(true);//直接出发全选事件，父组件调用子组件方法需要通过this.$refs.组件ref值.子组件方法名
      },
      addToRight() {
        let currentValue = this.value.slice();
        const itemsToBeMoved = [];
        const key = this.props.key;
        this.data.forEach(item => {
          const itemKey = item[key];
          if (
            this.leftChecked.indexOf(itemKey) > -1 &&
            this.value.indexOf(itemKey) === -1
          ) {
            itemsToBeMoved.push(itemKey);
          }
        });
        currentValue = this.targetOrder === 'unshift'
          ? itemsToBeMoved.concat(currentValue)
          : currentValue.concat(itemsToBeMoved);
        this.$emit('input', currentValue);
        this.$emit('change', currentValue, 'right', this.leftChecked);
      },

      clearQuery(which) {
        if (which === 'left') {
          this.$refs.leftPanel.query = '';
        } else if (which === 'right') {
          this.$refs.rightPanel.query = '';
        }
      }
    }
  };
</script>

该文件修改的主要难点在于如何通过按钮实现全选功能，摸索了半天，终于发现入口，通过调用handleAllCheckedChange(true),传入值为true即可完美实现，此处注意父组件调用子组件的方法需要通过this.$refs.组件ref值.子组件方法（参数）来调用

transferPanel.vue

<template>
  <div class="el-transfer-panel" style="border:1px solid #409EFF">
    <p class="el-transfer-panel__header">
      <el-checkbox v-show="false" 
        v-model="allChecked"
        @change="handleAllCheckedChange"
        :indeterminate="isIndeterminate">
        {{ title }}
        <span>{{ checkedSummary }}</span>
      </el-checkbox>
       {{ title }}
    </p>
    
    <div :class="['el-transfer-panel__body', hasFooter ? 'is-with-footer' : '']">
      <el-input
        class="el-transfer-panel__filter"
        v-model="query"
        size="small"
        :placeholder="placeholder"
        @mouseenter.native="inputHover = true"
        @mouseleave.native="inputHover = false"
        v-if="filterable">
        <i slot="prefix"
          :class="['el-input__icon', 'el-icon-' + inputIcon]"
          @click="clearQuery"
        ></i>
      </el-input>
      <el-checkbox-group
        v-model="checked"
        v-show="!hasNoMatch && data.length > 0"
        :class="{ 'is-filterable': filterable }"
        class="el-transfer-panel__list">
        <el-checkbox
          class="el-transfer-panel__item"
          :label="item[keyProp]"
          :disabled="item[disabledProp]"
          :key="item[keyProp]"
          v-for="item in filteredData">
          <option-content :option="item"></option-content>
          <span v-if="isRight" class="icon-close" style="float:right;margin-right:10px;width:20px;margin-top:5px;line-height:20px;text-align:center;height:20px;background-color:#ddd;border-radius:50%;">×</span>
        </el-checkbox><!--此处加了个判断是否为右边框给其加上相应的关闭按钮，isRight通过属性值进行传入-->
      </el-checkbox-group>
      <p
        class="el-transfer-panel__empty"
        v-show="hasNoMatch">{{ t('el.transfer.noMatch') }}</p>
      <p
        class="el-transfer-panel__empty"
        v-show="data.length === 0 && !hasNoMatch">{{ t('el.transfer.noData') }}</p>
    </div>
    <p class="el-transfer-panel__footer" v-if="hasFooter">
      <slot></slot>
    </p>
  </div>
</template>

<script>
  import ElCheckboxGroup from 'element-ui/packages/checkbox-group';
  import ElCheckbox from 'element-ui/packages/checkbox';
  import ElInput from 'element-ui/packages/input';
  import Locale from 'element-ui/src/mixins/locale';

  export default {
    mixins: [Locale],

    name: 'ElTransferPanel',

    componentName: 'ElTransferPanel',

    components: {
      ElCheckboxGroup,
      ElCheckbox,
      ElInput,
      OptionContent: {
        props: {
          option: Object
        },
        render(h) {
          const getParent = vm => {
            if (vm.$options.componentName === 'ElTransferPanel') {
              return vm;
            } else if (vm.$parent) {
              return getParent(vm.$parent);
            } else {
              return vm;
            }
          };
          const panel = getParent(this);
          const transfer = panel.$parent || panel;
          return panel.renderContent
            ? panel.renderContent(h, this.option)
            : transfer.$scopedSlots.default
              ? transfer.$scopedSlots.default({ option: this.option })
              : <span>{ this.option[panel.labelProp] || this.option[panel.keyProp] }</span>;
        }
      }
    },

    props: {
      data: {
        type: Array,
        default() {
          return [];
        }
      },
      renderContent: Function,
      placeholder: String,
      title: String,
      filterable: Boolean,
      isRight:Boolean,
      format: Object,
      filterMethod: Function,
      defaultChecked: Array,
      props: Object
    },

    data() {
      return {
        checked: [],
        allChecked: false,
        query: '',
        inputHover: false,
        checkChangeByUser: true
      };
    },

    watch: {
      checked(val, oldVal) {
        this.updateAllChecked();
        if (this.checkChangeByUser) {
          const movedKeys = val.concat(oldVal)
            .filter(v => val.indexOf(v) === -1 || oldVal.indexOf(v) === -1);
          this.$emit('checked-change', val, movedKeys);
        } else {
          this.$emit('checked-change', val);
          console.log("Check by User");
          this.checkChangeByUser = true;
        }
      },

      data() {
        const checked = [];
        const filteredDataKeys = this.filteredData.map(item => item[this.keyProp]);
        this.checked.forEach(item => {
          if (filteredDataKeys.indexOf(item) > -1) {
            checked.push(item);
          }
        });
        this.checkChangeByUser = false;
        this.checked = checked;
      },

      checkableData() {
        this.updateAllChecked();
      },

      defaultChecked: {
        immediate: true,
        handler(val, oldVal) {
          if (oldVal && val.length === oldVal.length &&
            val.every(item => oldVal.indexOf(item) > -1)) return;
          const checked = [];
          const checkableDataKeys = this.checkableData.map(item => item[this.keyProp]);
          val.forEach(item => {
            if (checkableDataKeys.indexOf(item) > -1) {
              checked.push(item);
            }
          });
          this.checkChangeByUser = false;
          this.checked = checked;
        }
      }
    },

    computed: {
      filteredData() {
        return this.data.filter(item => {
          if (typeof this.filterMethod === 'function') {
            return this.filterMethod(this.query, item);
          } else {
            const label = item[this.labelProp] || item[this.keyProp].toString();
            return label.toLowerCase().indexOf(this.query.toLowerCase()) > -1;
          }
        });
      },

      checkableData() {
        return this.filteredData.filter(item => !item[this.disabledProp]);
      },

      checkedSummary() {
        const checkedLength = this.checked.length;
        const dataLength = this.data.length;
        const { noChecked, hasChecked } = this.format;
        if (noChecked && hasChecked) {
          return checkedLength > 0
            ? hasChecked.replace(/\${checked}/g, checkedLength).replace(/\${total}/g, dataLength)
            : noChecked.replace(/\${total}/g, dataLength);
        } else {
          return `${ checkedLength }/${ dataLength }`;
        }
      },

      isIndeterminate() {
        const checkedLength = this.checked.length;
        return checkedLength > 0 && checkedLength < this.checkableData.length;
      },

      hasNoMatch() {
        return this.query.length > 0 && this.filteredData.length === 0;
      },

      inputIcon() {
        return this.query.length > 0 && this.inputHover
          ? 'circle-close'
          : 'search';
      },

      labelProp() {
        return this.props.label || 'label';
      },

      keyProp() {
        return this.props.key || 'key';
      },

      disabledProp() {
        return this.props.disabled || 'disabled';
      },

      hasFooter() {
        return !!this.$slots.default;
      }
    },

    methods: {
      updateAllChecked() {
        const checkableDataKeys = this.checkableData.map(item => item[this.keyProp]);
        this.allChecked = checkableDataKeys.length > 0 &&
          checkableDataKeys.every(item => this.checked.indexOf(item) > -1);
      },

      handleAllCheckedChange(value) {
        console.log("value",value);
        this.checked = value
          ? this.checkableData.map(item => item[this.keyProp])
          : [];
      },

      clearQuery() {
        if (this.inputIcon === 'circle-close') {
          this.query = '';
        }
      }
    }
  };
</script>

通过上面对elementui穿梭框的自定义样式，可类比其他组件的自定义修改