element/examples/docs/en-US/transfer.md

<style>
  .demo-transfer {
    .transfer-footer {
      margin-left: 15px;
      padding: 6px 5px;
    }
  }
</style>

<script>
  export default {
    data() {
      const generateData = _ => {
        const data = [];
        for (let i = 1; i <= 15; i++) {
          data.push({
            key: i,
            label: `Option ${ i }`,
            disabled: i % 4 === 0
          });
        }
        return data;
      };
      const generateData2 = _ => {
        const data = [];
        const states = ['California', 'Illinois', 'Maryland', 'Texas', 'Florida', 'Colorado', 'Connecticut '];
        const initials = ['CA', 'IL', 'MD', 'TX', 'FL', 'CO', 'CT'];
        states.forEach((city, index) => {
          data.push({
            label: city,
            key: index,
            initial: initials[index]
          });
        });
        return data;
      };
      const generateData3 = _ => {
        const data = [];
        for (let i = 1; i <= 15; i++) {
          data.push({
            value: i,
            desc: `Option ${ i }`,
            disabled: i % 4 === 0
          });
        }
        return data;
      };
      return {
        data: generateData(),
        data2: generateData2(),
        data3: generateData3(),
        value1: [1, 4],
        value2: [],
        value3: [1],
        value4: [],
        filterMethod(query, item) {
          return item.initial.toLowerCase().indexOf(query.toLowerCase()) > -1;
        },
        renderFunc(h, option) {
          return <span>{ option.key } - { option.label }</span>;
        }
      };
    },

    methods: {
      handleChange(value, direction, movedKeys) {
        console.log(value, direction, movedKeys);
      }
    }
  };
</script>

## Transfer

### Basic usage
:::demo Data is passed to Transfer via the `data` attribute. The data needs to be an object array, and each object should have these attributes: `key` being the identification of the data item, `label` being the displayed text, and `disabled` indicating if the data item is disabled. Items inside the target list are in sync with the variable binding to `v-model`, and the value of that variable is an array of target item keys. So, if you don't want the target list be initially empty, you can initialize the `v-model` with an array.
```html
<template>
  <el-transfer
    v-model="value1"
    :data="data">
  </el-transfer>
</template>

<script>
  export default {
    data() {
      const generateData = _ => {
        const data = [];
        for (let i = 1; i <= 15; i++) {
          data.push({
            key: i,
            label: `Option ${ i }`,
            disabled: i % 4 === 0
          });
        }
        return data;
      };
      return {
        data: generateData(),
        value1: [1, 4]
      };
    }
  };
</script>
```
:::

### Filterable

You can search and filter data items.

:::demo Set the `filterable` attribute to `true` to enable filter mode. By default, if the data item `label` contains the search keyword, it will be included in the search result. Also, you can implement you own filter method with the `filter-method` attribute. It takes a method and passes search keyword and each data item to it whenever the keyword changes. For a certain data item, if the method returns true, it will be included in the result list.
```html
<template>
  <el-transfer
    filterable
    :filter-method="filterMethod"
    filter-placeholder="State Abbreviations"
    v-model="value2"
    :data="data2">
  </el-transfer>
</template>

<script>
  export default {
    data() {
      const generateData2 = _ => {
        const data = [];
        const states = ['California', 'Illinois', 'Maryland', 'Texas', 'Florida', 'Colorado', 'Connecticut '];
        const initials = ['CA', 'IL', 'MD', 'TX', 'FL', 'CO', 'CT'];
        states.forEach((city, index) => {
          data.push({
            label: city,
            key: index,
            initial: initials[index]
          });
        });
        return data;
      };
      return {
        data2: generateData2(),
        value2: [],
        filterMethod(query, item) {
          return item.initial.toLowerCase().indexOf(query.toLowerCase()) > -1;
        }
      };
    }
  };
</script>
```
:::

### Customizable

You can customize list titles, button texts, render function for data items, checking status texts in list footer and list footer contents.

:::demo Use `titles`, `button-texts`, `render-content` and `format` to respectively customize list titles, button texts, render function for data items, checking status texts in list header. For list footer contents, two named slots are provided: `left-footer` and `right-footer`. Plus, if you want some items initially checked, you can use `left-default-checked` and `right-default-checked`. Finally, this example demonstrate the `change` event. Note that this demo can't run in jsfiddle because it doesn't support JSX syntax. In a real project, `render-content` will work if relevant dependencies are correctly configured.
```html
<template>
  <el-transfer
    v-model="value3"
    filterable
    :left-default-checked="[2, 3]"
    :right-default-checked="[1]"
    :render-content="renderFunc"
    :titles="['Source', 'Target']"
    :button-texts="['To left', 'To right']"
    :format="{
      noChecked: '${total}',
      hasChecked: '${checked}/${total}'
    }"
    @change="handleChange"
    :data="data">
    <el-button class="transfer-footer" slot="left-footer" size="small">Operation</el-button>
    <el-button class="transfer-footer" slot="right-footer" size="small">Operation</el-button>
  </el-transfer>
</template>

<style>
  .transfer-footer {
    margin-left: 20px;
    padding: 6px 5px;
  }
</style>

<script>
  export default {
    data() {
      const generateData = _ => {
        const data = [];
        for (let i = 1; i <= 15; i++) {
          data.push({
            key: i,
            label: `Option ${ i }`,
            disabled: i % 4 === 0
          });
        }
        return data;
      };
      return {
        data: generateData(),
        value3: [1],
        renderFunc(h, option) {
          return <span>{ option.key } - { option.label }</span>;
        }
      };
    },

    methods: {
      handleChange(value, direction, movedKeys) {
        console.log(value, direction, movedKeys);
      }
    }
  };
</script>
```
:::

### Prop aliases

By default, Transfer looks for `key`, `label` and `disabled` in a data item. If your data items have different key names, you can use the `props` attribute to define aliases.
:::demo The data items in this example do not have `key`s or `label`s, instead they have `value`s and `desc`s. So you need to set aliases for `key` and `label`.
```html
<template>
  <el-transfer
    v-model="value4"
    :props="{
      key: 'value',
      label: 'desc'
    }"
    :data="data3">
  </el-transfer>
</template>

<script>
  export default {
    data() {
      const generateData3 = _ => {
        const data = [];
        for (let i = 1; i <= 15; i++) {
          data.push({
            value: i,
            desc: `Option ${ i }`,
            disabled: i % 4 === 0
          });
        }
        return data;
      };
      return {
        data3: generateData3(),
        value4: []
      };
    }
  };
</script>
```
:::

### Attributes
| Attribute | Description | Type  | Accepted Values | Default |
|---------- |-------- |---------- |-------------  |-------- |
| data | data source | array[{ key, label, disabled }] | — | [ ] |
| filterable | whether Transfer is filterable | boolean | — | false |
| filter-placeholder | placeholder for the filter input | string | — | Enter keyword |
| filter-method | custom filter method | function | — | — |
| target-order | order strategy for elements in the target list. If set to `original`, the elements will keep the same order as the data source. If set to `push`, the newly added elements will be pushed to the bottom. If set to `unshift`, the newly added elements will be inserted on the top | string | original / push / unshift | original |
| titles | custom list titles | array | — | ['List 1', 'List 2'] |
| button-texts | custom button texts | array | — | [ ] |
| render-content | custom render function for data items | function(h, option) | — | — |
| format | texts for checking status in list header | object{noChecked, hasChecked} | — | { noChecked: '${checked}/${total}', hasChecked: '${checked}/${total}' } |
| props | prop aliases for data source | object{key, label, disabled} | — | — |
| left-default-checked | key array of initially checked data items of the left list | array | — | [ ] |
| right-default-checked | key array of initially checked data items of the right list | array | — | [ ] |

### Slot
| Name | Description |
|------|--------|
| left-footer | content of left list footer |
| right-footer | content of right list footer |

### Methods
| Method | Description | Parameters |
| ---- | ---- | ---- |
| clearQuery | clear the filter keyword of a certain panel | 'left' / 'right' |

### Events
| Event Name | Description | Parameters |
|---------- |-------- |---------- |
| change | triggers when data items change in the right list | key array of current data items in the right list, transfer direction (left or right), moved item keys |