Scriptrunner

[Stanislav]

What i should write in a behaviour if i want field "due date" be shown only if priority is "To time" and the main question what to write to make "due date" required field and only when it shown. 

[Peter-Dave Sheehan]

I would write it like this:

import com.atlassian.jira.issue.IssueConstantImpl

def priority = getFieldById(getFieldChanged())
def selectedPriority = ((IssueConstantImpl) priority.value).name
def SV = getFieldById("duedate")
def isToTime = selectedPriority == "To time"
SV.setHidden(isToTime).setRequired(!isToTime)

[Stanislav]

I made the hidden option. Now need to make it required only if shown on a create screen.

import com.atlassian.jira.issue.IssueConstantImpl

def priority = getFieldById(getFieldChanged())
def selectedPriority = ((IssueConstantImpl) priority.getValue()).getName()

def SV = getFieldByName("due date")

if ( selectedPriority == "To time") {
SV.setHidden(false)
} else {
SV.setHidden(true)
}

[Max Lim _Adaptavist_]

like @Peter-Dave Sheehan posted. You need to use

setRequired(true/false)

 to set the field required.