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i got  error  "Unable to call non-designated initializer as super constructor", when  i try to inherit WKWebView  in ios.

Seems like you already found an issue with explanations(<https://github.com/JetBrains/kotlin-native/issues/2010>). One can use only designated initializers when inheriting,  for this class they are `initWithFrame:configuration`  and `initWithCoder` . I’ve made this snippet to prove, that it should work correctly:
```import kotlinx.cinterop.*
import platform.WebKit.WKWebView
import platform.WebKit.WKWebViewConfiguration
import platform.Foundation.NSZeroRect

class myWebView : WKWebView(frame = NSZeroRect.readValue(), configuration = WKWebViewConfiguration())```

wow,it works. but how can i know which constructor is designated initializers?

That’s where the problem comes, in fact. One can check the frameworks headers contents manually, for example in the WKWebView.h there are such lines:
```- (instancetype)initWithFrame:(CGRect)frame configuration:(WKWebViewConfiguration *)configuration NS_DESIGNATED_INITIALIZER;
- (nullable instancetype)initWithCoder:(NSCoder *)coder NS_DESIGNATED_INITIALIZER;```
the `NS_DESIGNATED_INITIALIZER`  macro is what you need.