I am attempting to implement a solution from How to set canBecomeKeyWindow? Into my native C application using Objective-C runtime (The app is already written with objective C Runtime). Is there a way to create a subclass purely in Objective-C Runtime?
Right now I just create NSWindow object but need to be able to create my own so I can override the function specified in that question.
objc_msgSend((id)objc_getClass("NSWindow"), sel_registerName("alloc"));
The signature of can_become_key_window_true is slightly incorrect. According to the documentation (https://developer.apple.com/documentation/objectivec/objective-c_runtime/imp?language=objc) the function should have at least two arguments: "self" and "_cmd". So the signature should be like:
static bool can_become_key_window_true(__unused id _self, __unused SEL _cmd) {
return true;
}
You could also use #encode to construct the type encoding for the function.
char encoding[10]; // should be enough
snprintf(encoding, 10, "%s%s%s", #encode(BOOL), #encode(id), #encode(SEL));
... or you could get a method from UIWindow and get its type encoding like:
Method m = class_getInstanceMethod(objc_lookUpClass("UIWindow"), sel_getUid("canBecomeKeyWindow"));
const char *encoding = method_getTypeEncoding(m);
And as you might have noticed you could use sel_getUid() instead of sel_registerName as you expect this selector to be already registered by this time (because you are about to override an existing method).
To allocate a new instance you could use
window = class_createInstance(__UIWindow);
Figured it out after a lot of code searching:
// Subclass NSWindow with overridden function
Class __NSWindow =
objc_allocateClassPair(objc_getClass("NSWindow"), "__NSWindow", 0);
class_addMethod(__NSWindow,
sel_registerName("canBecomeKeyWindow"),
(IMP)can_become_key_window_true, "B#:");
objc_registerClassPair(__NSWindow);
// Allocate a new __NSWindow
window = objc_msgSend((id)__NSWindow, sel_registerName("alloc"));
And then can_become_key_window_true is defined as:
static bool can_become_key_window_true() {
return true;
}
I use objc_allocateClassPair to subclass the object and return a Class of that object. Then I use class_addMethod to override the method canBecomeKeyWindow. And finally use objc_registerClassPair to register my new class before using it as I would a normal NSWindow.
Related
I created some classes with Ruby's C API. I want to create a function whose behavior will change depending on the class of the Ruby object.
I tried to use is_a? from Ruby, however, I don't think it's the good way to do this. I checked "Creating Extension Libraries for Ruby" without success. The only direct way to check classes is with the default types.
I have my class "Klass" already created:
VALUE rb_cKlass = rb_define_class("Klass", rb_cObject);
And how I wanted to check if the class is the good one:
VALUE my_function(VALUE self, VALUE my_argument) {
if(rb_check_class(my_argument), rb_cKlass)) {
// do something if my_argument is an instance of Klass
} else {
return Qnil;
}
}
Is there a way to do this?
I came across this recently, and used the RBASIC_CLASS macro, but was getting segfaults in certain scenarios for some unexplained reason.
After scanning through ruby.h, I found the CLASS_OF macro, which returns the class as VALUE of a given object.
VALUE obj = INT2NUM(10);
VALUE klass = CLASS_OF(obj); // rb_cInteger
Using Ruby 2.5
Every ruby object is internally represented by RObject struct (I will copy the source here for the sake of future readers):
struct RObject {
struct RBasic basic;
union {
struct {
uint32_t numiv;
VALUE *ivptr;
void *iv_index_tbl; /* shortcut for RCLASS_IV_INDEX_TBL(rb_obj_class(obj)) */
} heap;
VALUE ary[ROBJECT_EMBED_LEN_MAX];
} as;
};
The very first member, RBasic, defines the class:
struct RBasic {
VALUE flags;
const VALUE klass;
}
To get an access to RBasic metadata of anything, one might use RBASIC macro:
RBASIC(my_argument)
To get the class directly, one might use RBASIC_CLASS macro:
RBASIC_CLASS(my_argument)
If you want to stay close to the is_a? Ruby fashion (i.e. check if any of the ancestors is the expected class), you could directly use the C implementation of is_a?, rb_obj_is_kind_of:
rb_obj_is_kind_of(my_argument, rb_cKlass) // Qtrue OR Qfalse
And since Qfalse == 0, you can just use that method as a condition:
VALUE my_function(VALUE self, VALUE my_argument) {
if(rb_obj_is_kind_of(my_argument, rb_cKlass)) {
// do something if my_argument is an instance of Klass
} else {
return Qnil;
}
}
To find this method, just check Object#is_a? documentation and click to toggle source, you'll see the C implementation if it is a C function (hence this will work for most of the standard lib).
I am trying to implement something like a HTMLCollection which is an array that can lose/gain elements without JS action.
duk_push_object(ctx);
duk_push_string(ctx, "length");
duk_push_c_function(ctx, my_length_getter, 1);
duk_def_prop(ctx, -3, DUK_DEFPROP_HAVE_GETTER);
duk_push_c_function(ctx, my_item_getter, 1);
duk_put_prop_string(ctx, -2, "item");
Doing it like above I get an object on which I can read the my_array.length property and get an item by calling method my_array.item(index). But I don't get an item by using my_array[index].
If I replace the first line above by
duk_push_array(ctx);
I get an error that the length property is not configurable.
Is it possible to achieve what I want? An array with 'lazy' element binding? I have the impression that NetSurf somehow manages to do this but haven't quite worked out how ...
Ecmascript provides two main standard mechanisms for property virtualization: getters/setters (accessors) and the Proxy object. Getters/setters are limited to properties you explicitly set up beforehand so they don't always work for fully virtualizing an object, but a Proxy object can capture among other things all property reads and writes.
You should be able to implement your use case using a Proxy. Duktape implements a subset of the Proxy traps (documented in http://duktape.org/guide.html#es6-proxy). As a minimal example of capturing all property reads and writes (but forwarding them to the target):
var target = { foo: 'hello' };
var proxy = new Proxy(target, {
get: function (targ, key) {
print('get', key);
// may also return a virtualized value
return targ[key];
},
set: function (targ, key, val) {
print('set', key, val);
// may also capture (virtualize) write, or reject write
targ[key] = val;
return true; // indicate write was allowed
}
});
print(proxy.foo);
proxy.bar = 123;
Running with "duk" this prints:
get foo
hello
set bar 123
How do you define a static extension method in Kotlin? Is this even possible? I currently have an extension method as shown below.
public fun Uber.doMagic(context: Context) {
// ...
}
The above extension can be invoked on an instance.
uberInstance.doMagic(context) // Instance method
but how do I make it static method like shown below.
Uber.doMagic(context) // Static or class method
To achieve Uber.doMagic(context), you can write an extension to the companion object of Uber (the companion object declaration is required):
class Uber {
companion object {}
}
fun Uber.Companion.doMagic(context: Context) { }
This is what the official documentation says:
Kotlin generates static methods for package-level functions. Kotlin
can also generate static methods for functions defined in named
objects or companion objects if you annotate those functions as
#JvmStatic. For example:
Kotlin static methods
class C {
companion object {
#JvmStatic fun foo() {}
fun bar() {}
}
}
Now, foo() is static in Java, while bar() is not:
C.foo(); // works fine
C.bar(); // error: not a static method
I actually had this exact question 30 minutes ago, so I started digging around and couldn't find any solution or workaround for this, BUT while searching I found this section on the Kotlinglang website that states that:
Note that extensions can be defined with a nullable receiver type. Such extensions can be called on an object variable even if its value is null.
So then I had the craziest idea ever, why not define an extension function with a nullable receiver (without actually using that receiver) and then call it on a null object!
So I tried that, and it worked pretty well, but it looked so ugly. It was like this:
(null as Type?).staticFunction(param1, param2)
So I went around that by creating a val in my extensions file of the receiver type that had a value of null and then use it in my other class.
So, as an example, here is how I implemented a "static" extension function for the Navigation class in Android:
In my NavigationExtensions.kt file:
val SNavigation: Navigation? = null
fun Navigation?.createNavigateOnClickListener(#IdRes resId: Int, args: Bundle? = null, navOptions: NavOptions? = null,
navigationExtras: Navigator.Extras? = null) : (View) -> Unit {
//This is just implementation details, don't worry too much about them, just focus on the Navigation? part in the method declaration
return { view: View -> view.navigate(resId, args, navOptions, navigationExtras) }
}
In the code that uses it:
SNavigation.createNavigateOnClickListener(R.id.action_gameWonFragment_to_gameFragment)
Obviously, this isn't a class name, it is just a variable of the class type that has a null value. This is obviously ugly on the extension maker side (because they have to create the variable) and on the developer side (because they have to use the SType format instead of the actual class name), but it is the closest that can be achieved right now compared to actual static functions. Hopefully, the Kotlin language makers will respond to the issue that was created and add that feature in the language.
Since I keep coming across this when searching, here's a different approach I haven't seen anyone mention that works in a static way and it works with generics!
Extension definitions:
// Extension function
fun <T> KClass<T>.doSomething() = /* do something */
// Extension Property
val <T> KClass<T>.someVal get() = /* something */
Usage:
MyType::class.doSomething()
MyType::class.someVal
As you can see, the trick is attaching the extension function to the KClass of the type instead since that can be referenced statically.
You can create a static method with using Companion object like:
class Foo {
// ...
companion object {
public fun bar() {
// do anything
}
}
}
and then you can call it like:
class Baz {
// ...
private fun callBar() {
Foo.bar()
}
}
Recomend you to look at this link. As you can see there, you just should declare method at the top-level of the package (file):
package strings
public fun joinToString(...): String { ... }
This is equal to
package strings;
public class JoinKt {
public static String joinToString(...) { ... }
}
With constans everything are the same. This declaration
val UNIX_LINE_SEPARATOR = "\n"
is equal to
public static final String UNIX_LINE_SEPARATOR = "\n";
I also required the ability to extend a Java object with a static method and found the best solution for me was to create a Kotlin object that extended the Java class and add my method there.
object Colour: Color(){
fun parseColor(r: Int?, g: Int?, b: Int?) = parseColor(String.format("#%02x%02x%02x", r, g, b))
}
invocation:
val colour = Colour.parseColor(62, 0, 100)
I'm also quite fond of having the possibility to add static extension methods in Kotlin. As a workaround for now I'm adding the exntension method to multiple classes instead of using one static extension method in all of them.
class Util
fun Util.isDeviceOnline(context: Context): Boolean {
val connMgr = context.getSystemService(Context.CONNECTIVITY_SERVICE) as ConnectivityManager
val networkInfo = connMgr.activeNetworkInfo
return networkInfo != null && networkInfo.isConnected
}
fun Activity.isDeviceOnline(context: Context) = { Util().isDeviceOnline(context) }
fun OkHttpClient.isDeviceOnline(context: Context) = { Util().isDeviceOnline(context) }
To create an extension method in kotlin you have to create a kotlin file(not a class) then declare your method in the file
Eg:
public fun String.toLowercase(){
// **this** is the string object
}
Import the function in the class or file you are working on and use it.
I have a function that handles two types: NVector and NMatrix; the former is derived from the latter. This function is basically a specialized copy constructor. I want it to return an object of the same type as that upon which it was called, so, NVector returns NVector, not NMatrix.
static VALUE nm_init_modifiedcopy(VALUE self) {
// ... some code ...
// formerly, I had cNMatrix where klass is. But it could also be cNVector!
return Data_Wrap_Struct(klass, mark_func, delete_func, unwrapped_self_copy);
}
How do I get the class property of an object to pass into Data_Wrap_Struct?
Like clockwork, as soon as I ask a question on Stackoverflow, I find the answer.
The macro is CLASS_OF.
static VALUE nm_init_modifiedcopy(VALUE self) {
// ... some code ...
return Data_Wrap_Struct(CLASS_OF(self), mark_func, delete_func, unwrapped_self_copy);
}
On a lot of NSURLConnection examples I see the following lines:
NSURLConnection *theConnection = [[NSURLConnection alloc]initWithRequest:theRequest delegate:self];
if(theConnection)
{
webData = [[NSMutableData data]retain];
}
else
...
I wonder - what is this supposed to do? and why does it work? I thought that data is an accessor method, and since your not calling it on an instanciated object, it will return nil, and by retaining it you actually do nothing.
This is the way I have seen to get data on connections like this:
NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:[NSURLRequest requestWithURL:url] delegate:self startImmediately:YES];
if( connection )
{
while (!finished) {
[[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
}
}
finished is an ivar that gets set to YES on connectionDidFinishLoading:
Can anyone clear this up for me? Which should be used and what's the difference?
[NSMutableData data] is not an accessor but a so-called class method. You probably know [NSMutableData alloc], that too is a class method and means it is tied to the class but not an instance. The typical way to denote that a method is a class method is by prefixing it with a plus: +[NSMutableData data].
In this case, the method is inherited from the NSData class (but does return an NSMutableData instance, since you're calling it on that class).
An implementation might look like this:
#interface NSMutableData
+ (id)data
{
return [[[self alloc] init] autorelease];
}
#end
Note that self in this case is the NSMutableData class.
In other languages like C++, C# and Java (AFAIK) these would be methods that you specify with the static keyword.