status-desktop/docs/tips.md

tips and tricks

seeing output of macros

import macros

expandmacros:
  #code

then during compilation it will display what the expanded code looks like

Getting notified for QML properties changing

Each QML property has an onChange attached to it automatically.

For example, if you a property named name, it will have an onNameChanged. It follows the pattern: on + Property + Change.

Eg:

property int index: 0

onIndexChanged: {
    console.log('Index changed', index)
}

Async

import chronos

proc someFunction*(someParameter:int): Future[string] {.async.}=
  result = "Something"
  

var myResult = waitFor someFunction(1)

# If inside some async function
var myResult = await someFunction(6464435)

# to discard the result,
asyncCheck someFunction(2332)

nim-chronos API is compatible with https://nim-lang.org/docs/asyncdispatch.html so this page can be used to complement nim-chronos lack of documentation. (Wiki)

Updating data on a QAbstractListModel

While adding/removing values from a list is easy, updating the values of a list requires some extra manipulation:

proc updateRecord(idx: int, newValue: string) =
    self.myList[idx] = newValue;
    var topLeft = self.createIndex(idx,0,nil)
    var bottomRight = self.createIndex(idx,0,nil)
    self.dataChanged(topLeft, bottomRight, @[RoleNames.SomeRole.int, RoleNames.AnotherRole.int, RoleNames.SomeOtherRole.int])

If more than one record is being updated at once, change the topLeft's and bottomRight's self.createIndex first parameter to indicate the initial row number and the final row number that were affected.

To refresh the whole table, I think you can use 0 as the first parameter for createIndex for both topLeft and bottomRight.

The final attribute of dataChanged is a non-empty sequence of RoleNames containing the attributes that were updated

Error Handling and Custom Errors

Raising Custom errors

type
  CustomError* = object of Exception # CatchableError/Defect

try:
  raise newException(CustomError, "Some error message")
except CustomError as e:
  echo e.msg

Raising Custom Errors with custom data (and parent Error)

type
  CustomError* = object of Exception
     customField*: string

type CustomErrorRef = ref CustomError

try:
  raise CustomErrorRef(msg: "Some error message", customField: "Some custom error data", parent: (ref ValueError)(msg: "foo bar"))
except CustomError as e:
  echo e.msg & ": " & e.customField
  echo "Original: " & e.parent.msg

Implementing custom Error helpers with default values

type
  CustomError* = object of Exception
    customField*: string

type CustomErrorRef = ref CustomError

proc newCustomError*(customData: string): CustomErrorRef =
  result = CustomErrorRef(msg: "This is some custom error message", customField: customData, parent: (ref ValueError)(msg: "Value error"))