Debug view hierarchy in Xcode 7.3 fails

Question

This function fails with runtime error:

-[UIWindow viewForFirstBaselineLayout]: unrecognized selector sent to instance 0x7fb9dae257d0

Anybo

Answer 1

Looks like Xcode 7.3 uses viewForFirstBaselineLayout property to draw the UI. But this property is marked as available since iOS 9.0.

[UIView viewForFirstBaselineLayout] method should be used for the version prior to iOS 9.0. It seems the guys from Apple didn't consider this case.

Answer 2

Yes. when click the debug view hierarchy button ,the page has nothing, and print "[UIWindow viewForFirstBaselineLayout]: unrecognized selector sent to instance 0x7fb9dae257d0" .

To solved it, just be sure you are using the iOS systom not below iOS 9.0 and you will still use that function freely.

Answer 3

I got the view debugger working again by placing the following fix in my project:

#ifdef DEBUG

#import <UIKit/UIKit.h>
#import <objc/runtime.h>

@implementation UIView (FixViewDebugging)

+ (void)load
{
    Method original = class_getInstanceMethod(self, @selector(viewForBaselineLayout));
    class_addMethod(self, @selector(viewForFirstBaselineLayout), method_getImplementation(original), method_getTypeEncoding(original));
    class_addMethod(self, @selector(viewForLastBaselineLayout), method_getImplementation(original), method_getTypeEncoding(original));
}

@end

#endif

When your project loads, the load method will execute, causing viewForFirstBaselineLayout and viewForLastBaselineLayout to use the viewForBaselineLayout implementation if they are not currently implemented, so view debugging gets iOS8 flavor the behavior it was looking for.

To add this to your own project, create a new empty Objective-C file in your project and paste the contents in. You can name it whatever you want. I call mine "UIView+FixViewDebugging". If you are in a pure Swift project you do not need to create a bridging header. The file will be compiled into your project and you don't need to reference it.

Note this will only work for debug builds because of the #ifdef DEBUG. You can remove it but then you may accidentally compile this into your release builds (though it should have no ill side effects). If this method isn't working with these lines, check that your target has DEBUG=1 in Build Settings > Apple LLVM - Preprocessing > Preprocessor Macros > Debug.