使用反射SetString [英] Using reflection SetString
问题描述
type ProductionInfo struct {
StructA [] Entry
}
类型条目结构{
Field1 string
Field2 int
}
我想使用反射更改 Field1
的值,但返回的反射对象总是 CanSet()=假
。我能做什么?请参阅操场示例。
https:// play .golang.org / p / eM_KHC3kQ5
以下是代码:
func SetField(source interface {},fieldName string,fieldValue string){
v:= reflect.ValueOf(source)
tt:= reflect.TypeOf(source)
for k:= 0; k< tt.NumField(); k){
fieldValue:= reflect.ValueOf(v.Field(k))
fmt.Println(fieldValue.CanSet())
if fieldValue.CanSet(){
fieldValue.SetString(fieldValue.String())
}
}
}
func main(){
source:= ProductionInfo { }
source.StructA = append(source.StructA,Entry {Field1:A,Field2:2})
SetField(source,Field1,NEW_VALUE)
多重错误。让我们对它们进行迭代。
首先,您传递的值 ProductionInfo
,而不是<$ c $的值c> Entry 要修改的字段,所以首先将其更改为:
SetField(source .StructA [0],Field1,NEW_VALUE)
接下来,非指针)值。你不能用反射修改非指针结构的字段,因为那样只会修改一个将被丢弃的副本。为了避免这种情况(并进一步混淆),这是不允许的( CanSet()
返回 false
)。所以你必须传递一个指向结构体的指针:
SetField(& source.StructA [0],Field1, NEW_VALUE)
现在位于 SetField()
reflect.ValueOf(source)
将描述传入的指针。您可以使用 Value.Elem()
导航到 reflect.Value
$ b
v:= reflect.ValueOf(source).Elem ()
现在它起作用了。修改后的代码:
func SetField(source interface {},fieldName string,fieldValue string){
v:= reflect。 ValueOf(source).Elem()
fmt.Println(v.FieldByName(fieldName).CanSet())
如果v.FieldByName(fieldName).CanSet() {
v.FieldByName(fieldName).SetString(fieldValue)
}
}
func main(){
source:= ProductionInfo {}
source.StructA = append(source.StructA,Entry {Field1:A,Field2:2})
fmt.Println(Before:,source.StructA [0])
SetField(& source.StructA [0],Field1,NEW_VALUE)
fmt.Println(After:,source.StructA [0])
}
输出(在 Go Playground ):
之前:{A 2}
true
后:{NEW_VALUE 2}
I have a struct like this one:
type ProductionInfo struct {
StructA []Entry
}
type Entry struct {
Field1 string
Field2 int
}
I would like to change the value of Field1
using reflection but the reflect object returned always CanSet() = false
. What can I do? See playground example.
https://play.golang.org/p/eM_KHC3kQ5
Here is the code:
func SetField(source interface{}, fieldName string, fieldValue string) {
v := reflect.ValueOf(source)
tt := reflect.TypeOf(source)
for k := 0; k < tt.NumField(); k++ {
fieldValue := reflect.ValueOf(v.Field(k))
fmt.Println(fieldValue.CanSet())
if fieldValue.CanSet() {
fieldValue.SetString(fieldValue.String())
}
}
}
func main() {
source := ProductionInfo{}
source.StructA = append(source.StructA, Entry{Field1: "A", Field2: 2})
SetField(source, "Field1", "NEW_VALUE")
}
Multiple errors. Let's iterate over them.
First, you pass a value of ProductionInfo
and not a value of Entry
whose field you want to modify, so first change it to:
SetField(source.StructA[0], "Field1", "NEW_VALUE")
Next, you are passing a (non-pointer) value. You can't modify the fields of a non-pointer struct with reflection, because that would only modify a copy which would be discarded. In order to avoid this (and further confusion), this is not allowed (CanSet()
returns false
). So you have to pass a pointer to the struct:
SetField(&source.StructA[0], "Field1", "NEW_VALUE")
Now inside SetField()
the reflect.ValueOf(source)
will describe the passed pointer. You may use Value.Elem()
to navigate to the reflect.Value
of the pointed object (the struct value):
v := reflect.ValueOf(source).Elem()
And now it works. Modified code:
func SetField(source interface{}, fieldName string, fieldValue string) {
v := reflect.ValueOf(source).Elem()
fmt.Println(v.FieldByName(fieldName).CanSet())
if v.FieldByName(fieldName).CanSet() {
v.FieldByName(fieldName).SetString(fieldValue)
}
}
func main() {
source := ProductionInfo{}
source.StructA = append(source.StructA, Entry{Field1: "A", Field2: 2})
fmt.Println("Before: ", source.StructA[0])
SetField(&source.StructA[0], "Field1", "NEW_VALUE")
fmt.Println("After: ", source.StructA[0])
}
Output (try it on the Go Playground):
Before: {A 2}
true
After: {NEW_VALUE 2}
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