I try to understand the whole GObject stuff and tried a class with three properties,
where two properties have getter and setters: 'example-property-a', 'example-property-b'
Each emit the notify signal different.
'example-property-a' emits, whenever the property changed its value.
'example-property-b' emits, whenever the property is set.
for 'example-property-c' i dont use a getter or setter. i use the GObject instance methods.
instance.set_property ([ property name STR] , [value STR] );
instance.get_property ([ property name STR] , [value GValue] );
https://docs.gtk.org/gobject/method.Object.get_property.html says a GValue is needed as parameter.
But i get an error :g_object_get_property: can't retrieve property 'example-property-c' of type 'gchararray' as value of type 'GValue'
hm ... how to get a gchararray? - the complete class try
const GOBJECT = imports.gi.GObject;
//-- prefix: 'go_' ... instances of classes and classes themselves, which inherit from GOBJECT.Object have this prefix
const go_Example = GOBJECT.registerClass(
{
GTypeName: 'SubclassExample',
Properties: {
'example-property-a': GOBJECT.ParamSpec.double('example-property-a', '', '', GOBJECT.ParamFlags.READWRITE, Number.MIN_SAFE_INTEGER, Number.MAX_SAFE_INTEGER, 0),
'example-property-b': GOBJECT.ParamSpec.boolean('example-property-b', '', '', GOBJECT.ParamFlags.READWRITE, true),
'example-property-c': GOBJECT.ParamSpec.string('example-property-c', '', '', GOBJECT.ParamFlags.READWRITE, null) },
Signals: {
'example-signal': { flags: GOBJECT.SignalFlags.RUN_LAST, param_types: [GOBJECT.TYPE_STRING], accumulator: GOBJECT.AccumulatorType.TRUE_HANDLED, return_type: GOBJECT.TYPE_BOOLEAN } }
},
class go_Example extends GOBJECT.Object
{
_init (properties) //-- _init ... name of the constructor in GObject classes
{
//-- set standard defined above in properties
this._example_property_a=0;
this._example_property_b=true;
this.example_property_c=null;
super._init(properties);
}
//-- 'example_property_a' get, set link on '_example_property_a' -> notify, only if value has changed
get example_property_a () { return this._example_property_a; }
set example_property_a (value) { if (this._example_property_a === value) return; this._example_property_a = value; this.notify ("example-property-a"); }
//-- 'example_property_b' get, set link on '_example_property_b'; notify, if value is set
get example_property_b () { return this._example_property_b; }
set example_property_b (value) { this._example_property_b = value; this.notify ("example-property-b"); }
//-- no get, set of example_propertyC -> notify over GOBJECT.Object.set_property function
});
let go_Obj=new go_Example ({example_property_a:12.5585, example_property_b:true, example_property_c: "hello world"});
let GValue_RV=new GOBJECT.Value; //-- return Value
GValue_RV.init(GOBJECT.TYPE_STRING)
go_Obj.connect ("notify::example-property-c", function (instance, ParamSpec) {log (instance+" - "+ParamSpec.get_name ());});
go_Obj.set_property ("example-property-c","hello");
go_Obj.get_property ("example-property-c",GValue_RV);
log (GValue_RV.get_string());
here i construct a GValue for returning the value of get_property
let GValue_RV=new GOBJECT.Value; //-- return Value
GValue_RV.init(GOBJECT.TYPE_STRING)
whats wrong?
other questions- if i construct a GObject.Object instance, can i install a ParamSpec property on a special object instance, because i only found install properties on a complete class?
Usually you won't want to use GObject.get_property() or GObject.set_property() in GJS. Instead you should just use the native accessors and allow GJS to do the heavy lifting for you:
const myObject = new MyObject();
// Getting a property
let stringValue = myObject.example_property_c;
// Setting a property
myObject.example_property_c = 'string value';
There is an introduction to GObject and a more thorough guide on subclassing on the gjs.guide website:
The Basics of GObject: Properties
GObject Subclassing: Properties
if i construct a GObject.Object instance, can i install a ParamSpec property on a special object instance, because i only found install properties on a complete class?
No, you can only install GObject properties on a class when it is defined, not on an instance. You can, however, add native JavaScript properties with Object.defineProperty().
Related
The CSSRule docs in MDN states that the CSSRule.type property is deprecated and is not clear to me what should be used instead if one wants to check the type of CSSRule. Adding some code for reference.
const isStyleOrImportRule = (rule: CSSRule): boolean => {
// 1 -> CSSRule.STYLE_RULE
// 3 -> CSSRule.IMPORT_RULE
return [1,3].includes(rule.type)
}
There is a better way to do this and avoiding deprecation issues referencing the constructor function name.
const isStyleOrImportRule = (rule: CSSRule): boolean => {
return ['CSSStyleRule', 'CSSImportRule'].includes(rule.constructor.name)
}
I have an Angular component that gets a TranslocoService injected into the constructor. The point of this component is to use the key provided as the output of the transform method in the event the key isn't found. This is done to make migrating existing components easier so I don't have to do them all at once.
The problem I'm having is that if I do this in the constructor in my component the config setting doesn't seem to have any affect.
this.translocoService.config.missingHandler.logMissingKey = false;
What am I missing here?
The translate function is as follows:
transform(contentKey: string, l10nBasePath: string): string {
const translatedText: string = this.translocoService.translate(l10nBasePath + '.' + contentKey);
if (translatedText !== null) {
return translatedText;
}
return contentKey;
}
I am writing a generic unmarshaller. It converts graph DB data to generated TypeScript (1.8.7) model classes. The input is JSON. The output should be an instance of a model class.
My ultimate goal is to create something like Hibernate OGM, only for Tinkerpop Frames and TypeScript, with REST endpoint in the middle.
What's the right way to pass a class as a parameter and reach it's static members? I want to have something like this:
SomeModel some = <SomeModel> unmarshaller.fromJSON({/*Object from JSON*/}, SomeModel);
I've tried to write a method.
Not sure if I am heading in the right direction, feel free to suggest different approaches.
public fromJSON(input: Object, clazz: typeof FrameModel): FrameModel
{
// This only demonstrates access to Framemodel's metadata
// about original Java model classes.
clazz.graphPropertyMapping;
clazz.graphRelationMapping;
let result = {};
...
return result;
}
...
But when I tried to execute this on Plunker, I got execution errors with unuseful stacktrace.
The model superclass looks like this:
/**
* Things common to all Frames models on the Typescript side.
*/
export class FrameModel
{
// Model metadata
static discriminator: string;
static graphPropertyMapping: { [key:string]:string; };
static graphRelationMapping: { [key:string]:string; };
// Each instance needs a vertex ID
private vertexId: number;
public getVertexId(): number {
return this.vertexId;
}
}
Sample model class:
import {TestPlanetModel} from './TestPlanetModel';
import {TestShipModel} from './TestShipModel';
export class TestGeneratorModel extends FrameModel
{
static discriminator: string = 'TestGenerator';
static graphPropertyMapping: { [key:string]:string; } = {
bar: 'boo',
name: 'name',
rank: 'rank',
};
static graphRelationMapping: { [key:string]:string; } = {
colonizes: 'colonizedPlanet',
commands: 'ship',
};
boo: string;
name: string;
rank: string;
public colonizedPlanet: TestPlanetModel[]; // edge label 'colonizedPlanet'
public ship: TestShipModel; // edge label 'ship'
}
I haven't found much material on reflection and class handling in TypeScript.
I know how I would do this in Java.
I know how I would do this in JavaScript.
I understand that I might achieve similar results with decorators, but having fields or static fields seemed a bit simpler, for generated models.
You've maybe already noticed that class members cannot have const keyword. But you could go with static instead. Also member should be public if you want it to be accessible from outside world.
public static graphPropertyMapping: { [key:string]:string; } = {
bar: 'boo',
name: 'name',
rank: 'rank',
};
As for creating result instance:
let result = new clazz();
//copy properties
return result;
If I understand you correctly then here's something to help you get started:
interface Model {}
interface ModelData {}
interface MyModelConstructor<M extends Model, D extends ModelData> {
new(data: D): M;
// static members
graphPropertyMapping: any;
graphRelationMapping: any;
}
class Unmarshaller {
public fromJSON<T>(input: string | ModelData, ctor: MyModelConstructor<T, ModelData>): T {
let data: ModelData = (typeof input === "string") ? JSON.parse(input) : input;
let propertyMapping = ctor.graphPropertyMapping;
let relationMapping = ctor.graphRelationMapping;
// do whatever with the mappings
return new ctor(input);
}
}
(code in playground)
I don't know how your models look like, so I hope this is close enough.
I recently released an enhanced version of the TypeScript compiler that allows exactly what you are expecting: read all (static or not) fields metadata from a class. For example you can write:
interface MyInterface {
active:boolean;
description: string;
}
class MyClass {
id: number;
name: string;
myComplexField: MyInterface;
}
function printMembers(clazz: Class) {
let fields = clazz.members.filter(m => m.type.kind !== 'function'); //exclude methods.
for(let field of fields) {
let typeName = field.type.kind;
if(typeName === 'class' || typeName === 'interface') {
typeName = (<Class | Interface>field.type).name;
}
console.log(`Field ${field.name} of ${clazz.name} has type: ${typeName}`);
}
}
printMembers(MyClass.getClass());
this is the output:
$ node main.js
Field id of MyClass has type: number
Field name of MyClass has type: string
Field myComplexField of MyClass has type: MyInterface
Of course, if you change the members property access of clazz to statics you will retrieve all static members. These information can be accessed at coding time too, so you can use autocompletion.
You can do the same with Interfaces metadata. Simply write MyInterface for example, and access its members.
You can find the project here.
I'm not sure of the best approach for handling scoping of "this" in TypeScript.
Here's an example of a common pattern in the code I am converting over to TypeScript:
class DemonstrateScopingProblems {
private status = "blah";
public run() {
alert(this.status);
}
}
var thisTest = new DemonstrateScopingProblems();
// works as expected, displays "blah":
thisTest.run();
// doesn't work; this is scoped to be the document so this.status is undefined:
$(document).ready(thisTest.run);
Now, I could change the call to...
$(document).ready(thisTest.run.bind(thisTest));
...which does work. But it's kinda horrible. It means that code can all compile and work fine in some circumstances, but if we forget to bind the scope it will break.
I would like a way to do it within the class, so that when using the class we don't need to worry about what "this" is scoped to.
Any suggestions?
Update
Another approach that works is using the fat arrow:
class DemonstrateScopingProblems {
private status = "blah";
public run = () => {
alert(this.status);
}
}
Is that a valid approach?
You have a few options here, each with its own trade-offs. Unfortunately there is no obvious best solution and it will really depend on the application.
Automatic Class Binding
As shown in your question:
class DemonstrateScopingProblems {
private status = "blah";
public run = () => {
alert(this.status);
}
}
Good/bad: This creates an additional closure per method per instance of your class. If this method is usually only used in regular method calls, this is overkill. However, if it's used a lot in callback positions, it's more efficient for the class instance to capture the this context instead of each call site creating a new closure upon invoke.
Good: Impossible for external callers to forget to handle this context
Good: Typesafe in TypeScript
Good: No extra work if the function has parameters
Bad: Derived classes can't call base class methods written this way using super.
Bad: The exact semantics of which methods are "pre-bound" and which aren't create an additional non-typesafe contract between your class and its consumers.
Function.bind
Also as shown:
$(document).ready(thisTest.run.bind(thisTest));
Good/bad: Opposite memory/performance trade-off compared to the first method
Good: No extra work if the function has parameters
Bad: In TypeScript, this currently has no type safety
Bad: Only available in ECMAScript 5, if that matters to you
Bad: You have to type the instance name twice
Fat arrow
In TypeScript (shown here with some dummy parameters for explanatory reasons):
$(document).ready((n, m) => thisTest.run(n, m));
Good/bad: Opposite memory/performance trade-off compared to the first method
Good: In TypeScript, this has 100% type safety
Good: Works in ECMAScript 3
Good: You only have to type the instance name once
Bad: You'll have to type the parameters twice
Bad: Doesn't work with variadic parameters
Another solution that requires some initial setup but pays off with its invincibly light, literally one-word syntax is using Method Decorators to JIT-bind methods through getters.
I've created a repo on GitHub to showcase an implementation of this idea (it's a bit lengthy to fit into an answer with its 40 lines of code, including comments), that you would use as simply as:
class DemonstrateScopingProblems {
private status = "blah";
#bound public run() {
alert(this.status);
}
}
I haven't seen this mentioned anywhere yet, but it works flawlessly. Also, there is no notable downside to this approach: the implementation of this decorator -- including some type-checking for runtime type-safety -- is trivial and straightforward, and comes with essentially zero overhead after the initial method call.
The essential part is defining the following getter on the class prototype, which is executed immediately before the first call:
get: function () {
// Create bound override on object instance. This will hide the original method on the prototype, and instead yield a bound version from the
// instance itself. The original method will no longer be accessible. Inside a getter, 'this' will refer to the instance.
var instance = this;
Object.defineProperty(instance, propKey.toString(), {
value: function () {
// This is effectively a lightweight bind() that skips many (here unnecessary) checks found in native implementations.
return originalMethod.apply(instance, arguments);
}
});
// The first invocation (per instance) will return the bound method from here. Subsequent calls will never reach this point, due to the way
// JavaScript runtimes look up properties on objects; the bound method, defined on the instance, will effectively hide it.
return instance[propKey];
}
Full source
The idea can be also taken one step further, by doing this in a class decorator instead, iterating over methods and defining the above property descriptor for each of them in one pass.
Necromancing.
There's an obvious simple solution that doesn't require arrow-functions (arrow-functions are 30% slower), or JIT-methods through getters.
That solution is to bind the this-context in the constructor.
class DemonstrateScopingProblems
{
constructor()
{
this.run = this.run.bind(this);
}
private status = "blah";
public run() {
alert(this.status);
}
}
You can write an autobind method to automatically bind all functions in the constructor of the class:
class DemonstrateScopingProblems
{
constructor()
{
this.autoBind(this);
}
[...]
}
export function autoBind(self)
{
for (const key of Object.getOwnPropertyNames(self.constructor.prototype))
{
const val = self[key];
if (key !== 'constructor' && typeof val === 'function')
{
// console.log(key);
self[key] = val.bind(self);
} // End if (key !== 'constructor' && typeof val === 'function')
} // Next key
return self;
} // End Function autoBind
Note that if you don't put the autobind-function into the same class as a member function, it's just autoBind(this); and not this.autoBind(this);
And also, the above autoBind function is dumbed down, to show the principle.
If you want this to work reliably, you need to test if the function is a getter/setter of a property as well, because otherwise - boom - if your class contains properties, that is.
Like this:
export function autoBind(self)
{
for (const key of Object.getOwnPropertyNames(self.constructor.prototype))
{
if (key !== 'constructor')
{
// console.log(key);
let desc = Object.getOwnPropertyDescriptor(self.constructor.prototype, key);
if (desc != null)
{
if (!desc.configurable) {
console.log("AUTOBIND-WARNING: Property \"" + key + "\" not configurable ! (" + self.constructor.name + ")");
continue;
}
let g = desc.get != null;
let s = desc.set != null;
if (g || s)
{
var newGetter = null;
var newSetter = null;
if (g)
newGetter = desc.get.bind(self);
if (s)
newSetter = desc.set.bind(self);
if (newGetter != null && newSetter == null) {
Object.defineProperty(self, key, {
get: newGetter,
enumerable: desc.enumerable,
configurable: desc.configurable
});
}
else if (newSetter != null && newGetter == null) {
Object.defineProperty(self, key, {
set: newSetter,
enumerable: desc.enumerable,
configurable: desc.configurable
});
}
else {
Object.defineProperty(self, key, {
get: newGetter,
set: newSetter,
enumerable: desc.enumerable,
configurable: desc.configurable
});
}
continue; // if it's a property, it can't be a function
} // End if (g || s)
} // End if (desc != null)
if (typeof (self[key]) === 'function')
{
let val = self[key];
self[key] = val.bind(self);
} // End if (typeof (self[key]) === 'function')
} // End if (key !== 'constructor')
} // Next key
return self;
} // End Function autoBind
In your code, have you tried just changing the last line as follows?
$(document).ready(() => thisTest.run());
In Objective-C, I would normally use something like this:
static NSString *kViewTransformChanged = #"view transform changed";
// or
static const void *kViewTransformChanged = &kViewTransformChanged;
[clearContentView addObserver:self
forKeyPath:#"transform"
options:NSKeyValueObservingOptionNew
context:&kViewTransformChanged];
I have two overloaded methods to choose from to add an observer for KVO with the only difference being the context argument:
clearContentView.addObserver(observer: NSObject?, forKeyPath: String?, options: NSKeyValueObservingOptions, context: CMutableVoidPointer)
clearContentView.addObserver(observer: NSObject?, forKeyPath: String?, options: NSKeyValueObservingOptions, kvoContext: KVOContext)
With Swift not using pointers, I'm not sure how to dereference a pointer to use the first method.
If I create my own KVOContext constant for use with the second method, I wind up with it asking for this:
let test:KVOContext = KVOContext.fromVoidContext(context: CMutableVoidPointer)
EDIT: What is the difference between CMutableVoidPointer and KVOContext? Can someone give me an example how how to use them both and when I would use one over the other?
EDIT #2: A dev at Apple just posted this to the forums: KVOContext is going away; using a global reference as your context is the way to go right now.
There is now a technique officially recommended in the documentation, which is to create a private mutable variable and use its address as the context.
(Updated for Swift 3 on 2017-01-09)
// Set up non-zero-sized storage. We don't intend to mutate this variable,
// but it needs to be `var` so we can pass its address in as UnsafeMutablePointer.
private static var myContext = 0
// NOTE: `static` is not necessary if you want it to be a global variable
observee.addObserver(self, forKeyPath: …, options: [], context: &MyClass.myContext)
override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey: Any]?, context: UnsafeMutableRawPointer?) {
if context == &myContext {
…
}
else {
super.observeValue(forKeyPath: keyPath, of: object, change: change, context: context)
}
}
Now that KVOContext is gone in Xcode 6 beta 3, you can do the following. Define a global (i.e. not a class property) like so:
let myContext = UnsafePointer<()>()
Add an observer:
observee.addObserver(observer, forKeyPath: …, options: nil, context: myContext)
In the observer:
override func observeValueForKeyPath(keyPath: String!, ofObject object: AnyObject!, change: [NSObject : AnyObject]!, context: UnsafePointer<()>) {
if context == myContext {
…
} else {
super.observeValueForKeyPath(keyPath, ofObject: object, change: change, context: context)
}
}
Swift 4 - observing contentSize change on UITableViewController popover to fix incorrect size
I had been searching for an answer to change to a block based KVO because I was getting a swiftlint warning and it took me piecing quite a few different answers together to get to the right solution. Swiftlint warning:
Block Based KVO Violation: Prefer the new block based KVO API with keypaths when using Swift 3.2 or later. (block_based_kvo).
My use case was to present a popover controller attached to a button in a Nav bar in a view controller and then resize the popover once it's showing - otherwise it would be too big and not fitting the contents of the popover. The popover itself was a UITableViewController that contained static cells, and it was displayed via a Storyboard segue with style popover.
To setup the block based observer, you need the following code inside your popover UITableViewController:
// class level variable to store the statusObserver
private var statusObserver: NSKeyValueObservation?
// Create the observer inside viewWillAppear
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
statusObserver = tableView.observe(\UITableView.contentSize,
changeHandler: { [ weak self ] (theTableView, _) in self?.popoverPresentationController?.presentedViewController.preferredContentSize = theTableView.contentSize
})
}
// Don't forget to remove the observer when the popover is dismissed.
override func viewDidDisappear(_ animated: Bool) {
if let observer = statusObserver {
observer.invalidate()
statusObserver = nil
}
super.viewDidDisappear(animated)
}
I didn't need the previous value when the observer was triggered, so left out the options: [.new, .old] when creating the observer.
Update for Swift 4
Context is not required for block-based observer function and existing #keyPath() syntax is replaced with smart keypath to achieve swift type safety.
class EventOvserverDemo {
var statusObserver:NSKeyValueObservation?
var objectToObserve:UIView?
func registerAddObserver() -> Void {
statusObserver = objectToObserve?.observe(\UIView.tag, options: [.new, .old], changeHandler: {[weak self] (player, change) in
if let tag = change.newValue {
// observed changed value and do the task here on change.
}
})
}
func unregisterObserver() -> Void {
if let sObserver = statusObserver {
sObserver.invalidate()
statusObserver = nil
}
}
}
Complete example using Swift:
//
// AppDelegate.swift
// Photos-MediaFramework-swift
//
// Created by Phurg on 11/11/16.
//
// Displays URLs for all photos in Photos Library
//
// #see http://stackoverflow.com/questions/30144547/programmatic-access-to-the-photos-library-on-mac-os-x-photokit-photos-framewo
//
import Cocoa
import MediaLibrary
// For KVO: https://developer.apple.com/library/content/documentation/Swift/Conceptual/BuildingCocoaApps/AdoptingCocoaDesignPatterns.html#//apple_ref/doc/uid/TP40014216-CH7-ID12
private var mediaLibraryLoaded = 1
private var rootMediaGroupLoaded = 2
private var mediaObjectsLoaded = 3
#NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {
#IBOutlet weak var window: NSWindow!
var mediaLibrary : MLMediaLibrary!
var allPhotosAlbum : MLMediaGroup!
func applicationDidFinishLaunching(_ aNotification: Notification) {
NSLog("applicationDidFinishLaunching:");
let options:[String:Any] = [
MLMediaLoadSourceTypesKey: MLMediaSourceType.image.rawValue, // Can't be Swift enum
MLMediaLoadIncludeSourcesKey: [MLMediaSourcePhotosIdentifier], // Array
]
self.mediaLibrary = MLMediaLibrary(options:options)
NSLog("applicationDidFinishLaunching: mediaLibrary=%#", self.mediaLibrary);
self.mediaLibrary.addObserver(self, forKeyPath:"mediaSources", options:[], context:&mediaLibraryLoaded)
NSLog("applicationDidFinishLaunching: added mediaSources observer");
// Force load
self.mediaLibrary.mediaSources?[MLMediaSourcePhotosIdentifier]
NSLog("applicationDidFinishLaunching: done");
}
override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
NSLog("observeValue: keyPath=%#", keyPath!)
let mediaSource:MLMediaSource = self.mediaLibrary.mediaSources![MLMediaSourcePhotosIdentifier]!
if (context == &mediaLibraryLoaded) {
NSLog("observeValue: mediaLibraryLoaded")
mediaSource.addObserver(self, forKeyPath:"rootMediaGroup", options:[], context:&rootMediaGroupLoaded)
// Force load
mediaSource.rootMediaGroup
} else if (context == &rootMediaGroupLoaded) {
NSLog("observeValue: rootMediaGroupLoaded")
let albums:MLMediaGroup = mediaSource.mediaGroup(forIdentifier:"TopLevelAlbums")!
for album in albums.childGroups! {
let albumIdentifier:String = album.attributes["identifier"] as! String
if (albumIdentifier == "allPhotosAlbum") {
self.allPhotosAlbum = album
album.addObserver(self, forKeyPath:"mediaObjects", options:[], context:&mediaObjectsLoaded)
// Force load
album.mediaObjects
}
}
} else if (context == &mediaObjectsLoaded) {
NSLog("observeValue: mediaObjectsLoaded")
let mediaObjects:[MLMediaObject] = self.allPhotosAlbum.mediaObjects!
for mediaObject in mediaObjects {
let url:URL? = mediaObject.url
// URL does not extend NSObject, so can't be passed to NSLog; use string interpolation
NSLog("%#", "\(url)")
}
}
}
}