Go语言教程之边写边学：Golang中的反射：Reflect包的Field相关函数

NumField函数

返回给定结构中的字段数。

示例代码：

package main

import (
	"fmt"
	"reflect"
)

type T struct {
	A int
	B string
	C float64
	D bool
}

func main() {
	t := T{10, "ABCD", 15.20, true}
	typeT := reflect.TypeOf(t)
	fmt.Println(typeT.NumField()) // 4
}

field函数

Field函数用于访问结构字段的名称和类型。

示例代码：

package main

import (
	"fmt"
	"reflect"
)

type T struct {
	A int
	B string
	C float64
	D bool
}

func main() {
	t := T{10, "ABCD", 15.20, true}
	typeT := reflect.TypeOf(t)

	for i := 0; i < typeT.NumField(); i++ {
		field := typeT.Field(i)
		fmt.Println(field.Name, field.Type)
	}
}

输出：

A int
B string 
C float64
D bool

FieldByIndex函数

FieldByIndex函数用于获取index对应的嵌套字段

package main

import (
	"fmt"
	"reflect"
)

type First struct {
	A int
	B string
	C float64
}

type Second struct {
	First
	D bool
}

func main() {
	s := Second{First: First{10, "ABCD", 15.20}, D: true}
	t := reflect.TypeOf(s)

	fmt.Printf("%#v\n", t.FieldByIndex([]int{0}))
	fmt.Printf("%#v\n", t.FieldByIndex([]int{0, 0}))
	fmt.Printf("%#v\n", t.FieldByIndex([]int{0, 1}))
	fmt.Printf("%#v\n", t.FieldByIndex([]int{0, 2}))
	fmt.Printf("%#v\n", t.FieldByIndex([]int{1}))
}

输出：

reflect.StructField{Name:"First", PkgPath:"", Type:(*reflect.rtype)(0x4bda40), Tag:"", Offset:0x0, Index:[]int{0}, Anonymous:true}
reflect.StructField{Name:"A", PkgPath:"", Type:(*reflect.rtype)(0x4ad800), Tag:"", Offset:0x0, Index:[]int{0}, Anonymous:false} 
reflect.StructField{Name:"B", PkgPath:"", Type:(*reflect.rtype)(0x4adf80), Tag:"", Offset:0x8, Index:[]int{1}, Anonymous:false} 
reflect.StructField{Name:"C", PkgPath:"", Type:(*reflect.rtype)(0x4ad400), Tag:"", Offset:0x18, Index:[]int{2}, Anonymous:false}
reflect.StructField{Name:"D", PkgPath:"", Type:(*reflect.rtype)(0x4ad200), Tag:"", Offset:0x20, Index:[]int{1}, Anonymous:false

FieldByName函数

FieldByName函数用于通过给定的字段名称获取和设置结构字段值。

示例代码：

package main

import (
	"fmt"
	"reflect"
)

type T struct {
	A int
	B string
	C float64
}

func main() {
	s := T{10, "ABCD", 15.20}
	fmt.Println(reflect.ValueOf(&s).Elem().FieldByName("A"))
	fmt.Println(reflect.ValueOf(&s).Elem().FieldByName("B"))
	fmt.Println(reflect.ValueOf(&s).Elem().FieldByName("C"))

	reflect.ValueOf(&s).Elem().FieldByName("A").SetInt(50)
	reflect.ValueOf(&s).Elem().FieldByName("B").SetString("Test")
	reflect.ValueOf(&s).Elem().FieldByName("C").SetFloat(5.5)

	fmt.Println(reflect.ValueOf(&s).Elem().FieldByName("A"))
	fmt.Println(reflect.ValueOf(&s).Elem().FieldByName("B"))
	fmt.Println(reflect.ValueOf(&s).Elem().FieldByName("C"))
}

输出：

10
ABCD
15.2
50  
Test
5.5