status-desktop/docs/tips.md

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## tips and tricks
### seeing output of macros
```nimrod=
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
```nimrod
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](https://github.com/status-im/nim-chronos/wiki/AsyncDispatch-comparison))
## 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
```nim
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)
```nim
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
```nim
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"))
```