You can use UQuery to find elements from a visual tree. UQuery was inspired by JQuery and Linq, and is designed to limit dynamic memory allocation. This allows for optimal performance on mobile platforms.
You can use UQuery through the following extension methods:
Internally, the Q and Query methods use UQueryBuilder to construct a query. These extension methods reduce the verbosity of creating a UQueryBuilder.
To use UQuery to find elements, you must load and instantiate the UXML first, and then use Query or Q to construct selections rules on a root visual element.
Query returns a list of elements that match the selection rules. You can filter the return results of Query with the public methods of UQueryBuilder, such as First, Last, AtIndex, Children, and Where.
Q is the shorthand for Query<T>.First(). It returns the first element that matches the selection rules.
You can query elements by their name, their USS class, or their element type (C# type). You can also query with a predicate or make complex hierarchical queries.
The following sections use this example UXML to demonstrate how to find elements:
<UXML xmlns="UnityEngine.UIElements">
<VisualElement name="container1">
<Button name="OK" text="OK" />
<Button name="Cancel" text="Cancel" />
</VisualElement>
<VisualElement name="container2">
<Button name="OK" class="yellow" text="OK" />
<Button name="Cancel" text="Cancel" />
</VisualElement>
<VisualElement name="container3">
<Button name="OK" class="yellow" text="OK" />
<Button name="Cancel" class="yellow" text="Cancel" />
</VisualElement>
</UXML>
To find elements by their name, use Query(name: "element-name") or Q(name: "element-name"). You can omit name as it’s the first argument. For example:
The following example finds a list of elements named “Ok”:
List<VisualElement> result = root.Query("OK").ToList();
The following example use Query to find the first element named “Ok”:
VisualElement result = root.Query("OK").First(); //or VisualElement result = root.Q("OK");
The following example use Q to find the first element named “Ok”:
VisualElement result = root.Q("OK");
The following example finds the second element named “Ok”:
VisualElement result3 = root.Query("OK").AtIndex(1);
The following example finds the last element named “Ok”:
VisualElement result4 = root.Query("OK").Last();
To find elements by a USS class, use Query(className: "class-name") or Q(className: "class-name").
The following example finds all the elements that have the class “yellow” and assigns them to a list:
List<VisualElement> result = root.Query(className: "yellow").ToList();
The following example finds the first element that has the class “yellow”:
VisualElement result = root.Q(className: "yellow");
To find elements by their element type(C# type), use Query<Type> or Q<Type>.
The following example finds the first button and add a tool tip for it:
VisualElement result = root.Q<Button>();
result.tooltip = "This is a tooltip!";
The following example finds the third button:
VisualElement result = root.Query<Button>().AtIndex(2);
Note: You can only query by the actual type of the element, not base classes.
Other than to query element by name, class, and type, you can also use the Where method to select all elements that satisfy a predicate. The predicate must be a function callback that takes a single VisualElement argument.
The following example finds the all the elements with the “yellow” USS class that have no tool tips:
List<VisualElement> result = root.Query(className: "yellow").Where(elem => elem.tooltip == "").ToList();
You can combine name, class, and type to make complex hierarchical queries.
The following example finds the first button named “OK” that has a class of “yellow”:
VisualElement result = root.Query<Button>(className: "yellow", name: "OK").First();
The following example finds the child cancel button of the “container2”:
VisualElement result = root.Query<VisualElement>("container2").Children<Button>("Cancel").First();
You can use the ForEach method to operate directly on the query results.
The following example adds a tool tip for any elements that have no tool tips:
root.Query().Where(elem => elem.tooltip == "").ForEach(elem => elem.tooltip="This is a tooltip!");
Consider the following when you use UQuery:
QueryState struct (returned by the element.Query() method) and enumerate it to avoid creating lists. You can also construct a query once and execute it on different elements.VisualElement variables inside closures.