How do I add histogram to prometheus exporter in golang?

Here is the example of my code.Now I want add histogram in my code.
but I can't find a way to add histogram like this.

Is anybody could help me?
I am able to write histogram sample but I can't add it in my below code

package main
import (
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promhttp"
	"github.com/prometheus/common/log"
	"net/http"
)

type fooCollector struct {
	fooMetric *prometheus.Desc
}

func newFooCollector(label1 string) *fooCollector {
	return &fooCollector{
		fooMetric: prometheus.NewDesc("fff_metric",
			"Shows whether a foo has occurred in our cluster",
			nil, prometheus.Labels{"env":label1},
		),
		
	}
}

func (collector *fooCollector) Describe(ch chan<- *prometheus.Desc) {

	//Update this section with the each metric you create for a given collector
	ch <- collector.fooMetric
}

func (collector *fooCollector) Collect(ch chan<- prometheus.Metric) {

	ch <- prometheus.MustNewConstMetric(collector.fooMetric, prometheus.GaugeValue, 111111)

}
func main() {
	prometheus.MustRegister(newFooCollector("dev"))
	http.Handle("/metrics", promhttp.Handler())
	http.ListenAndServe(":80", nil)
}

finally I learned how histogram works.here is my code

package main
import (
"github.com/prometheus/client_golang/prometheus"
"github.com/prometheus/client_golang/prometheus/promhttp"
"net/http"
)
type fooCollector struct {
fooMetric *prometheus.Desc
}
//First,we define the variable of histogram
var (
hbrms_histovec = prometheus.NewHistogramVec(
prometheus.HistogramOpts{
Name:        "hbrms_histogram",
Help:        "hbrms_histogram",
ConstLabels: prometheus.Labels{"constname": "constvalue"},
Buckets: prometheus.ExponentialBuckets(50, 1.3, 15),//50*1.3,15times
},
[]string{"env"},
)
)
func newFooCollector() *fooCollector {
return &fooCollector{
fooMetric: prometheus.NewDesc("fff_metric",
"Shows whether a foo has occurred in our cluster",
nil, nil,
),
}
}
func (collector *fooCollector) Describe(ch chan<- *prometheus.Desc) {
ch <- collector.fooMetric
}
func (collector *fooCollector) Collect(ch chan<- prometheus.Metric) {
ch <- prometheus.MustNewConstMetric(collector.fooMetric, prometheus.CounterValue, float64(1))
// 2nd,we set metrics in this way instead of write to channel,we just find a way of calling the code below when we visit the url.
hbrms_histovec.WithLabelValues("val1").Observe(float64(10))
}
func main() {
reg := prometheus.NewPedanticRegistry()
reg.MustRegister(newFooCollector())
// finally,we register the metrics "hbrms_histovec" in this way
reg.MustRegister(hbrms_histovec)
gatherers := prometheus.Gatherers{reg}
h := promhttp.HandlerFor(gatherers,
promhttp.HandlerOpts{
ErrorHandling: promhttp.ContinueOnError,
})
http.HandleFunc("/metrics", func(w http.ResponseWriter, r *http.Request) {
h.ServeHTTP(w, r)
})
http.ListenAndServe(":80", nil)
}

You can just simply call .Collect(ch) method for each metric(thats both includes description and values). Also you don't need to extend default prometheus route handler - just be careful you don't have collision with default metric names

package main
import (
"github.com/prometheus/client_golang/prometheus"
"github.com/prometheus/client_golang/prometheus/promhttp"
"net/http"
)
type fooCollector struct {
fooMetric      *prometheus.GaugeVec
hmdrsHistogram *prometheus.HistogramVec
}
func newFooCollector() *fooCollector {
return &fooCollector{
fooMetric: prometheus.NewGaugeVec(prometheus.GaugeOpts{
Name: "fff_metric",
Help: "Shows whether a foo has occurred in our cluster",
}, []string{"country"}),
hmdrsHistogram: prometheus.NewHistogramVec(
prometheus.HistogramOpts{
Name:        "hbrms_histogram",
Help:        "hbrms_histogram",
ConstLabels: prometheus.Labels{"constname": "constvalue"},
Buckets:     prometheus.ExponentialBuckets(50, 1.3, 15), //50*1.3,15times
},
[]string{"env"},
),
}
}
func (collector *fooCollector) Describe(ch chan<- *prometheus.Desc) {
// don't need to manually call .Describe() here,
// because description was defined with prometheus.MustRegister method
//collector.fooMetric.Describe(ch)
//collector.hmdrsHistogram.Describe(ch)
}
func (collector *fooCollector) Collect(ch chan<- prometheus.Metric) {
v := 14 // get value from DB/External service/etc
collector.fooMetric.WithLabelValues("qwe").Set(float64(v))
collector.fooMetric.WithLabelValues("qwe").Set(v)
collector.fooMetric.Collect(ch)
collector.hmdrsHistogram.WithLabelValues("val1").Observe(float64(10))
collector.hmdrsHistogram.Collect(ch)
}
func RegisterFooCollector() {
fc := newFooCollector()
prometheus.MustRegister(fc)
}
func main() {
RegisterFooCollector()
// also includes default metrics
http.Handle("/metrics", promhttp.Handler())
err := http.ListenAndServe(":80", nil)
if err != nil {
return
}
}