# Cascader 级联选择

### 介绍

级联选择器，用于多层级数据的选择，典型场景为省市区选择。

### 安装

```js
import { createApp } from 'vue';
// vue
import { Cascader } from '@nutui/nutui';
// taro
import { Cascader } from '@nutui/nutui-taro';

const app = createApp();
app.use(Cascader);
```

### 基础用法

传入`options`列表。
```html
<nut-form>
  <nut-form-item label="选择地址">
    <input
      class="nut-input-text"
      @click="state.visible = true"
      :value="state.value"
      readonly
      placeholder="请选择地址"
      type="text"
    />
    <nut-cascader
      title="地址选择"
      v-model:visible="state.visible"
      v-model="state.value"
      @change="events.change"
      @path-change="events.pathChange"
      :options="state.options"
    ></nut-cascader>
  </nut-form-item>
</nut-form>
```

```javascript
setup() {
  const state = reactive({
    visible: false,
    value: ['湖南'],
    options: [
      {
        value: '浙江',
        text: '浙江',
        children: [
          {
            value: '杭州',
            text: '杭州',
            disabled: true,
            children: [
              { value: '西湖区', text: '西湖区' },
              { value: '余杭区', text: '余杭区' }
            ]
          },
          {
            value: '温州',
            text: '温州',
            children: [
              { value: '鹿城区', text: '鹿城区' },
              { value: '瓯海区', text: '瓯海区' }
            ]
          }
        ]
      },
      {
        value: '湖南',
        text: '湖南',
        disabled: true
      },
      {
        value: '福建',
        text: '福建',
        children: [
          {
            value: '福州',
            text: '福州',
            children: [
              { value: '鼓楼区', text: '鼓楼区' },
              { value: '台江区', text: '台江区' }
            ]
          }
        ]
      }
    ]
  });
  const events = {
    change(...args: any) {
      console.log('change', ...args);
    },
    pathChange(...args: any) {
      console.log('pathChange', ...args);
    },
  };

  return { state, events };
}
```

### 自定义属性名称

可通过`textKey`、`valueKey`、`childrenKey`指定属性名。
```html
<nut-form>
  <nut-form-item label="选择地址">
    <input
      class="nut-input-text"
      @click="state.visible = true"
      :value="state.value"
      readonly
      placeholder="请选择地址"
      type="text"
    />
    <nut-cascader
      title="地址选择"
      v-model:visible="state.visible"
      v-model="state.value"
      label-key="text"
      @change="events.change"
      @path-change="events.pathChange"
      value-key="text"
      children-key="items"
      :options="state.options"
    ></nut-cascader>
  </nut-form-item>
</nut-form>
```

```javascript
setup() {
  const state = reactive({
    visible: false,
    value: ['浙江', '杭州', '西湖区'],
    options: [
      {
        text: '浙江',
        items: [
          {
            text: '杭州',
            disabled: true,
            items: [{ text: '西湖区' }, { text: '余杭区' }]
          },
          {
            text: '温州',
            items: [{ text: '鹿城区' }, { text: '瓯海区' }]
          }
        ]
      },
      {
        text: '福建',
        items: [
          {
            text: '福州',
            items: [{ text: '鼓楼区' }, { text: '台江区' }]
          }
        ]
      }
    ]
  });
  const events = {
    change(...args: any) {
      console.log('change', ...args);
    },
    pathChange(...args: any) {
      console.log('pathChange', ...args);
    },
  };

  return { state, events };
}
```

### 动态加载

使用`lazy`标识是否需要动态获取数据，此时不传`options`代表所有数据都需要通过`lazyLoad`加载，首次加载通过`root`属性区分，当遇到非叶子节点时会调用`lazyLoad`方法，参数为当前节点和`resolve`方法，注意`resolve`方法必须调用，不传子节点时会被当做叶子节点处理。
```html
<nut-form>
  <nut-form-item label="选择地址">
    <input
      class="nut-input-text"
      @click="state.visible = true"
      :value="state.value"
      readonly
      placeholder="请选择地址"
      type="text"
    />
    <nut-cascader
      title="地址选择"
      v-model:visible="state.visible"
      v-model="state.value"
      @change="events.change"
      @path-change="events.pathChange"
      lazy
      :lazy-load="state.lazyLoad"
    ></nut-cascader>
  </nut-form-item>
</nut-form>
```

```javascript
setup() {
  const state = reactive({
    visible: false,
    value: ['A0', 'A12', 'A23', 'A32'],
    lazyLoad(node: any, resolve: (children: any) => void) {
      setTimeout(() => {
        // root表示第一层数据
        if (node.root) {
          resolve([
            { value: 'A0', text: 'A0' },
            { value: 'B0', text: 'B0' },
            { value: 'C0', text: 'C0' }
          ]);
        } else {
          const { value, level } = node;
          const text = value.substring(0, 1);
          const value1 = `${text}${level + 1}1`;
          const value2 = `${text}${level + 1}2`;
          const value3 = `${text}${level + 1}3`;
          resolve([
            { value: value1, text: value1, leaf: level >= 6 },
            { value: value2, text: value2, leaf: level >= 6 },
            { value: value3, text: value3, leaf: level >= 6 }
          ]);
        }
      }, 300);
    }
  });
  const events = {
    change(...args: any) {
      console.log('change', ...args);
    },
    pathChange(...args: any) {
      console.log('pathChange', ...args);
    },
  };

  return { state, events };
}
```

### 部分数据动态加载

```html
<nut-form>
  <nut-form-item label="选择地址">
    <input
      class="nut-input-text"
      @click="state.visible = true"
      :value="state.value"
      readonly
      placeholder="请选择地址"
      type="text"
    />
    <nut-cascader
      title="地址选择"
      v-model:visible="state.visible"
      v-model="state.value"
      @change="events.change"
      @path-change="events.pathChange"
      :options="state.options"
      lazy
      :lazy-load="state.lazyLoad"
    ></nut-cascader>
  </nut-form-item>
</nut-form>
```

```javascript
setup() {
  const state = reactive({
    visible: false,
    value: [],
    options: [
      { value: 'A0', text: 'A0' },
      {
        value: 'B0',
        text: 'B0',
        children: [
          { value: 'B11', text: 'B11', leaf: true },
          { value: 'B12', text: 'B12' }
        ]
      },
      { value: 'C0', text: 'C0' }
    ],
    lazyLoad(node: any, resolve: (children: any) => void) {
      setTimeout(() => {
        const { value, level } = node;
        const text = value.substring(0, 1);
        const value1 = `${text}${level + 1}1`;
        const value2 = `${text}${level + 1}2`;
        resolve([
          { value: value1, text: value1, leaf: level >= 2 },
          { value: value2, text: value2, leaf: level >= 1 }
        ]);
      }, 500);
    }
  });
  const events = {
    change(...args: any) {
      console.log('change', ...args);
    },
    pathChange(...args: any) {
      console.log('pathChange', ...args);
    },
  };

  return { state, events };
}
```

### 自动转换

如果你的数据为可转换为树形结构的扁平结构时，可以通过`convertConfig`告诉组件需要进行自动转换，`convertConfig`接受4个参数，`topId`为顶层节点的父级id，`idKey`为节点唯一id，`pidKey`为指向父节点id的属性名，存在`sortKey`将根据指定字段调用Array.prototype.sort()进行同层排序。


```html
<nut-form>
  <nut-form-item label="选择地址" @click="state.visible = true">
    <input
      class="nut-input-text"
      @click="state.visible = true"
      :value="state.value"
      readonly
      placeholder="请选择地址"
      type="text"
    />
    <nut-cascader
      title="地址选择"
      v-model:visible="state.visible"
      v-model="state.value"
      @change="events.change"
      @path-change="events.pathChange"
      :options="state.options"
      :convertConfig="state.convertConfig"
    ></nut-cascader>
  </nut-form-item>
</nut-form>
```

```javascript
setup() {
  const state = reactive({
    visible: false,
    value: ['广东省', '广州市'],
    convertConfig: {
      topId: null,
      idKey: 'id',
      pidKey: 'pid',
      sortKey: ''
    },
    options: [
      { value: '北京', text: '北京', id: 1, pid: null },
      { value: '朝阳区', text: '朝阳区', id: 11, pid: 1 },
      { value: '亦庄', text: '亦庄', id: 111, pid: 11 },
      { value: '广东省', text: '广东省', id: 2, pid: null },
      { value: '广州市', text: '广州市', id: 21, pid: 2 }
    ]
  });
  const events = {
    change(...args: any) {
      console.log('change', ...args);
    },
    pathChange(...args: any) {
      console.log('pathChange', ...args);
    },
  };

  return { state, events };
}
```

## API

### Props

| 参数          | 说明                                                  | 类型     | 默认值 |
| ------------- | ----------------------------------------------------- | -------- | ------ |
| v-model       | 选中值，双向绑定                                      | Array    | -      |
| options       | 级联数据                                              | Array    | -      |
| lazy          | 是否开启动态加载                                      | Boolean  | -      |
| lazy-load      | 动态加载回调，开启动态加载时生效                      | Function | -      |
| value-key      | 自定义`options`结构中`value`的字段                    | String   | -      |
| text-key       | 自定义`options`结构中`text`的字段                     | String   | -      |
| children-key   | 自定义`options`结构中`children`的字段                 | String   | -      |
| convert-config | 当options为可转换为树形结构的扁平结构时，配置转换规则 | Object   | -      |

### Events

| 事件名     | 说明             | 回调参数           |
| ---------- | ---------------- | ------------------ |
| change     | 选中值改变时触发 | (value, pathNodes) |
| pathChange | 选中项改变时触发 | (pathNodes)        |
