106 lines
3.0 KiB
Markdown
106 lines
3.0 KiB
Markdown
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## tips and tricks
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### seeing output of macros
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```nimrod=
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import macros
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expandmacros:
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#code
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```
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then during compilation it will display what the expanded code looks like
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### Getting notified for QML properties changing
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Each QML property has an `onChange` attached to it automatically.
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For example, if you a property named `name`, it will have an `onNameChanged`. It follows the pattern: `on` + Property + `Change`.
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Eg:
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```
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property int index: 0
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onIndexChanged: {
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console.log('Index changed', index)
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}
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```
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## Async
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```nimrod
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import chronos
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proc someFunction*(someParameter:int): Future[string] {.async.}=
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result = "Something"
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var myResult = waitFor someFunction(1)
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# If inside some async function
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var myResult = await someFunction(6464435)
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# to discard the result,
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asyncCheck someFunction(2332)
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```
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`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))
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## Updating data on a QAbstractListModel
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While adding/removing values from a list is easy, updating the values of a list requires some extra manipulation:
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```
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proc updateRecord(idx: int, newValue: string) =
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self.myList[idx] = newValue;
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var topLeft = self.createIndex(idx,0,nil)
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var bottomRight = self.createIndex(idx,0,nil)
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self.dataChanged(topLeft, bottomRight, @[RoleNames.SomeRole.int, RoleNames.AnotherRole.int, RoleNames.SomeOtherRole.int])
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```
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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.
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To refresh the whole table, I think you can use `0` as the first parameter for `createIndex` for both `topLeft` and `bottomRight`.
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The final attribute of `dataChanged` is a non-empty sequence of RoleNames containing the attributes that were updated
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## Error Handling and Custom Errors
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### Raising Custom errors
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```nim
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type
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CustomError* = object of Exception # CatchableError/Defect
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try:
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raise newException(CustomError, "Some error message")
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except CustomError as e:
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echo e.msg
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```
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### Raising Custom Errors with custom data (and parent Error)
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```nim
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type
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CustomError* = object of Exception
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customField*: string
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type CustomErrorRef = ref CustomError
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try:
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raise CustomErrorRef(msg: "Some error message", customField: "Some custom error data", parent: (ref ValueError)(msg: "foo bar"))
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except CustomError as e:
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echo e.msg & ": " & e.customField
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echo "Original: " & e.parent.msg
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```
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### Implementing custom Error helpers with default values
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```nim
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type
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CustomError* = object of Exception
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customField*: string
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type CustomErrorRef = ref CustomError
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proc newCustomError*(customData: string): CustomErrorRef =
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result = CustomErrorRef(msg: "This is some custom error message", customField: customData, parent: (ref ValueError)(msg: "Value error"))
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```
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