Checking Code Syntax

As you write code, Qt Design Studio checks code syntax. When Qt Design Studio spots a syntax error in your code it underlines it and shows error details when you move the mouse pointer over the error. Similarly, when you are working on an instance of a JavaScript object notation (JSON) entity, Qt Design Studio underlines errors in JSON data structure.

In addition to underlining, errors and warnings are marked with icons and annotated. When writing QML or JavaScript code, the annotations may contain error codes listed in JavaScript and QML Error Codes.

Specifying Line Annotation Positions

To specify the position where the annotations are displayed, select Tools > Options > Text Editor > Display > Line annotations, and then select whether to display the annotations directly next to the code, aligned to the right of the code, or in the right margin. Showing annotations between lines can be useful if there is usually not enough space to display annotations next to the text.

"Text Editor Display options"

If you hide the annotations by deselecting the check box, you can move the mouse pointer over an icon to view them.

JavaScript and QML Error Codes

You can run static checks on the QML and JavaScript code in your project to find common problems. To run the checks, select Tools > QML/JS > Run Checks or press Ctrl+Shift+C. The results are shown in the QML and QML Analysis filters of the Issues output pane.

Many of the error messages are similar to the ones in Douglas Crockford's JSLint tool. For more information about JSLint errors, see JSLint Error Explanations.

Id	Severity	Message	Description
M1	Error	Invalid value for enum
M2	Error	Enum value must be a string or a number
M3	Error	Number value expected
M4	Error	Boolean value expected
M5	Error	String value expected
M6	Error	Invalid URL
M7	Warning	File or directory does not exist
M8	Error	Invalid color
M9	Error	Anchor line expected
M10	Error	Duplicate property binding	See also: Duplicate key '{a}'.
M11	Error	Id expected	See also: Expected an identifier and instead saw '{a}' (a reserved word).
M14	Error	Invalid id	See also: Expected an identifier and instead saw '{a}' (a reserved word).
M15	Error	Duplicate id	Ids in a file must be unique. See also: Duplicate key '{a}'.
M16	Error	Invalid property name `name`
M17	Error	`Name` does not have members
M18	Error	`Field` is not a member of `object`
M19	Warning	Assignment in condition	It could be a typing error. If it is intentional, wrap the assignment in parentheses.
M20	Warning	Unterminated non-empty case block	Case blocks should either be empty or end in a flow control statement such as `break`, `return` or `continue`. Alternatively you can indicate intentional fall through by ending with a `// fall through` comment.
M23	Warning	Do not use `eval`	See also: eval is evil.
M28	Warning	Unreachable	Indicates that the underlined statement will never be executed.
M29	Warning	Do not use `with`	See also: Unexpected 'with'.
M30	Warning	Do not use comma expressions
M31	Warning	Unnecessary message suppression
M103	Warning	`Name` is already a formal parameter
M104	Warning	`Name` is already a function
M105	Warning	Var `name` is used before its declaration
M106	Warning	`Name` already is a var
M107	Warning	`Name` is declared more than once	Variables declared in a function are always visible everywhere in the function, even when declared in nested blocks or `for` statement conditions. Redeclaring a variable has no effect.
M108	Warning	Function `name` is used before its declaration	See also: {a} was used before it was defined.
M109	Warning	Do not use `Boolean` as a constructor	See also: Do not use {a} as a constructor.
M110	Warning	Do not use `String` as a constructor	See also: Do not use {a} as a constructor.
M111	Warning	Do not use `Object` as a constructor	See also: Do not use {a} as a constructor.
M112	Warning	Do not use `Array` as a constructor	See also: Do not use {a} as a constructor.
M113	Warning	Do not use `Function` as a constructor	See also: Do not use {a} as a constructor.
M114	Hint	The `function` keyword and the opening parenthesis should be separated by a single space	See also: Expected exactly one space between {a} and {b}.
M115	Warning	Do not use stand-alone blocks	Blocks do not affect variable scoping. Thus blocks that are not associated to `if`, `while`, etc. have no effect and should be avoided.
M116	Warning	Do not use void expressions
M117	Warning	Confusing pluses	See also: Confusing pluses.
M119	Warning	Confusing minuses	See also: Confusing minuses.
M121	Hint	Declare all function vars on a single line
M123	Hint	Unnecessary parentheses
M126	Warning	`==` and `!=` may perform type coercion, use `===` or `!==` to avoid it	The non-strict equality comparison is allowed to convert its arguments to a common type. That can lead to unexpected results such as `' \t\r\n' == 0` being true. Use the strict equality operators `===` and `!==` and be explicit about conversions you require.
M127	Warning	Expression statements should be assignments, calls or delete expressions only
M128	Error	A state cannot have the specified child item
M129	Error	Type cannot be instantiated recursively
M201	Hint	Place var declarations at the start of a function	See also: Move 'var' declarations to the top of the function.
M202	Hint	Use only one statement per line
M203	Warning	Imperative code is not supported in Qt Design Studio
M204	Warning	This QML type is not supported in Qt Design Studio
M205	Warning	Reference to parent QML type cannot be resolved correctly by Qt Design Studio
M206	Warning	This visual property binding cannot be evaluated in the local context and might not show up in Qt Design Studio as expected
M207	Warning	Qt Design Studio only supports states in the root QML type
M208	Error	This id might be ambiguous and is not supported in Qt Design Studio
M209	Error	This type (type name) is not supported as a root element in Qt Design Studio
M220	Error	This type (type name) is not supported as a root element of a UI file (.ui.qml)	For more information about supported QML types, see UI Files.
M221	Error	This type (type name) is not supported in a UI file (.ui.qml)	For more information about supported QML types, see UI Files.
M222	Error	Functions are not supported in a UI file (.ui.qml)	For a list of supported JavaScript functions, see Supported Methods.
M223	Error	JavaScript blocks are not supported in a UI file (.ui.qml)	For more information about supported features, see UI Files.
M224	Error	Behavior type is not supported in a UI file (.ui.qml)	For more information about supported QML types, see UI Files.
M225	Error	States are only supported in the root item in a UI file (.ui.qml)	For more information about supported features, see UI Files.
M226	Error	Referencing the parent of the root item is not supported in a UI file (.ui.qml)	For more information about supported features, see UI Files.
M227	Error	Do not mix translation functions in a UI file (.ui.qml)	Even though several different translation functions, such as `qsTr` and `qsTrId` are supported, you should pick one and use it consistently within a UI file. For more information, see Qt QML Methods.
M300	Error	Unknown component
M301	Error	Could not resolve the prototype `name` of `object`
M302	Error	Could not resolve the prototype `name`
M303	Error	Prototype cycle, the last non-repeated component is `name`
M304	Error	Invalid property type `name`
M305	Warning	`==` and `!=` perform type coercion, use `===` or `!==` to avoid it	See M126.
M306	Warning	Calls of functions that start with an uppercase letter should use `new`	By convention, functions that start with an uppercase letter are constructor functions that should only be used with `new`.
M307	Warning	Use `new` only with functions that start with an uppercase letter	See also: Do not use {a} as a constructor.
M308	Warning	Do not use `Number` as a constructor	See also: Do not use {a} as a constructor.
M309	Hint	Use spaces around binary operators
M310	Warning	Unintentional empty block, use ({}) for empty object literal
M311	Hint	Use `type` instead of `var` or `variant` to improve performance
M312	Error	Missing property `number`
M313	Error	Object value expected
M314	Error	Array value expected
M315	Error	`Value` value expected
M316	Error	Maximum number value is `number`
M317	Error	Minimum number value is `number`
M318	Error	Maximum number value is exclusive
M319	Error	Minimum number value is exclusive
M320	Error	String value does not match required pattern
M321	Error	Minimum string value length is `number`
M322	Error	Maximum string value length is `number`
M323	Error	`Number` elements expected in array value	See also: The array literal notation [] is preferable.
M324	Error	Hit maximum recursion limit visiting AST, the code model will be unreliable and most likely invalid
M325	Warning	Logical value does not depend on actual values
M326	Error	Components are only allowed to have a single child element	For more information, see Component.
M327	Warning	Components require a child element	For more information, see Component.
M400	Warning	Duplicate import	An import statement has been added twice. For more information, see Import Statements.

Resetting the Code Model

If you change the build and run kit when you have QML files open in the code editor, the code model might become corrupt. The following error message indicates that this might have happened: Using Qt Quick 1 code model instead of Qt Quick 2.

You can see the error message when you move the mouse pointer over code that Qt Design Studio underlines in the code editor or when you open a QML file in Qt Design Studio.

To reset the code model, select Tools > QML/JS > Reset Code Model.

Inspecting QML and JavaScript

To inspect QML and JavaScript properties, methods, and enums, move the cursor over them and select Tools > QML/JS > Inspect API for Element Under Cursor.

Automatically Formatting QML/JS Files

To automatically format QML/JS files upon saving, select Tools > Options > Qt Quick > QML/JS Editing > Enable auto format on file save.

Semantic Highlighting Completing Code

Available under certain Qt licenses.
Find out more.