Struct GKNSPredicateRule

Source

pub struct GKNSPredicateRule { /* private fields */ }

Available on crate feature GKRuleSystem only.

Expand description

A convenient subclass of GKRule that leverages existing NSPRedicate functionality for evaluating the predicate of the rule.

Implementations§

Source §

impl GKNSPredicateRule

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pub unsafe fn predicate(&self) -> Retained<NSPredicate>

The NSPredicate that is used inside this subclass’s implementation of evaluatePredicateWithSystem: In order to effectively use this class you must still override performActionWithSystem:

See: GKRule.evaluatePredicateWithSystem:

Source

pub unsafe fn initWithPredicate( this: Allocated<Self>, predicate: &NSPredicate, ) -> Retained<Self>

Initializes a new rule with the given NSPredicate

Source

pub unsafe fn evaluatePredicateWithSystem(&self, system: &GKRuleSystem) -> bool

Overridden here to call the predicate’s evaluateWithObject:substitutionVariables:, using sys as the object and the system’s state dictionary as the source of the substitution variables.

Returns: YES if the NSPredicate evaluation passes and the action needs to be performed, NO otherwise.

Source §

impl GKNSPredicateRule

Methods declared on superclass GKRule.

Source

pub unsafe fn ruleWithPredicate_assertingFact_grade( predicate: &NSPredicate, fact: &ProtocolObject<dyn NSObjectProtocol>, grade: c_float, ) -> Retained<Self>

Create a data-driven rule that uses NSPredicate and a single assert as the action.

§Safety

fact should be of the correct type.

Source

pub unsafe fn ruleWithPredicate_retractingFact_grade( predicate: &NSPredicate, fact: &ProtocolObject<dyn NSObjectProtocol>, grade: c_float, ) -> Retained<Self>

Short hand for data-driven rule that uses NSPredicate and a single retract as the action.

§Safety

fact should be of the correct type.

Source

pub unsafe fn ruleWithBlockPredicate_action( predicate: &DynBlock<dyn Fn(NonNull<GKRuleSystem>) -> Bool>, action: &DynBlock<dyn Fn(NonNull<GKRuleSystem>)>, ) -> Retained<Self>

Available on crate feature block2 only.

Short hand for making a rule that uses blocks for the predicate and action. This rule is not able to be archived using NSKeyedArchiver so use a subclass or NSPredicate based rule if serialization of the rule is needed.

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impl GKNSPredicateRule

Methods declared on superclass NSObject.

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pub unsafe fn init(this: Allocated<Self>) -> Retained<Self>

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pub unsafe fn new() -> Retained<Self>

Methods from Deref<Target = GKRule>§

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pub unsafe fn salience(&self) -> NSInteger

Salience defines the order in the rule agenda that the system will evaluate. A rule with higher salience will be evaluated before another rule in the agenda that has a lower salience.

Defaults to 0.

See: GKRuleSystem.agenda

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pub unsafe fn setSalience(&self, salience: NSInteger)

Setter for salience.

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pub unsafe fn evaluatePredicateWithSystem(&self, system: &GKRuleSystem) -> bool

Called by the rule system when it is this rule’s turn to be evaluated. If the predicate returns YES then the action for the rule will be performed. Once the action is performed the rule will move to the system’s executed list until the agenda is reset.

See: performAction

See: GKRuleSystem.agenda

See: GKRuleSystem.executed

See: GKRuleSystem.reset

Returns: YES is the predicate passes and the action needs to be performed, NO otherwise.

Source

pub unsafe fn performActionWithSystem(&self, system: &GKRuleSystem)

Performs the action consequence for the rule. This will only be called if the predicate evaluates to YES. Any facts asserted or retracted by the action on the system will cause the system to evaluate the agenda rule set again once the action completes.

Methods from Deref<Target = NSObject>§

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pub fn doesNotRecognizeSelector(&self, sel: Sel) -> !

Handle messages the object doesn’t recognize.

See Apple’s documentation for details.

Methods from Deref<Target = AnyObject>§

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pub fn class(&self) -> &'static AnyClass

Dynamically find the class of this object.

§Panics

May panic if the object is invalid (which may be the case for objects returned from unavailable init/new methods).

§Example

Check that an instance of NSObject has the precise class NSObject.

use objc2::ClassType;
use objc2::runtime::NSObject;

let obj = NSObject::new();
assert_eq!(obj.class(), NSObject::class());

Source

pub unsafe fn get_ivar<T>(&self, name: &str) -> &T
where T: Encode,

👎Deprecated: this is difficult to use correctly, use Ivar::load instead.

Use Ivar::load instead.

§Safety

The object must have an instance variable with the given name, and it must be of type T.

See Ivar::load_ptr for details surrounding this.

Source

pub fn downcast_ref<T>(&self) -> Option<&T>
where T: DowncastTarget,

Attempt to downcast the object to a class of type T.

This is the reference-variant. Use Retained::downcast if you want to convert a retained object to another type.

§Mutable classes

Some classes have immutable and mutable variants, such as NSString and NSMutableString.

When some Objective-C API signature says it gives you an immutable class, it generally expects you to not mutate that, even though it may technically be mutable “under the hood”.

So using this method to convert a NSString to a NSMutableString, while not unsound, is generally frowned upon unless you created the string yourself, or the API explicitly documents the string to be mutable.

See Apple’s documentation on mutability and on isKindOfClass: for more details.

§Generic classes

Objective-C generics are called “lightweight generics”, and that’s because they aren’t exposed in the runtime. This makes it impossible to safely downcast to generic collections, so this is disallowed by this method.

You can, however, safely downcast to generic collections where all the type-parameters are AnyObject.

§Panics

This works internally by calling isKindOfClass:. That means that the object must have the instance method of that name, and an exception will be thrown (if CoreFoundation is linked) or the process will abort if that is not the case. In the vast majority of cases, you don’t need to worry about this, since both root objects NSObject and NSProxy implement this method.

§Examples

Cast an NSString back and forth from NSObject.

use objc2::rc::Retained;
use objc2_foundation::{NSObject, NSString};

let obj: Retained<NSObject> = NSString::new().into_super();
let string = obj.downcast_ref::<NSString>().unwrap();
// Or with `downcast`, if we do not need the object afterwards
let string = obj.downcast::<NSString>().unwrap();

Try (and fail) to cast an NSObject to an NSString.

use objc2_foundation::{NSObject, NSString};

let obj = NSObject::new();
assert!(obj.downcast_ref::<NSString>().is_none());

Try to cast to an array of strings.

use objc2_foundation::{NSArray, NSObject, NSString};

let arr = NSArray::from_retained_slice(&[NSObject::new()]);
// This is invalid and doesn't type check.
let arr = arr.downcast_ref::<NSArray<NSString>>();

This fails to compile, since it would require enumerating over the array to ensure that each element is of the desired type, which is a performance pitfall.

Downcast when processing each element instead.

use objc2_foundation::{NSArray, NSObject, NSString};

let arr = NSArray::from_retained_slice(&[NSObject::new()]);

for elem in arr {
    if let Some(data) = elem.downcast_ref::<NSString>() {
        // handle `data`
    }
}