Add comprehensive error handling and logging to iOS screenshot API

Reverted to dispatch_async to avoid blocking the EDT, but added extensive
error handling and logging to diagnose the NullPointerException.

Changes to IOSNative.m:
- Reverted dispatch_sync back to dispatch_async (don't block EDT)
- Added @try/@catch block to catch Objective-C exceptions
- Added null checks for view, image, PNG data, and byte array
- Added NSLog statements at each step to trace execution
- All error paths now call onScreenshot with nil to complete the callback

Changes to IOSImplementation.java:
- Added try/catch around screenshot() call with logging
- Added try/catch in onScreenshot() with null checks
- Added logging when imageData is null
- Ensured callback is always invoked (with null on error)

This will provide detailed stack traces and logs to identify the exact
location of the NullPointerException.

Author: claude

Ports/iOSPort/nativeSources/IOSNative.m

@@ -5212,28 +5212,52 @@ void com_codename1_impl_ios_IOSNative_updatePersonWithRecordID___int_com_codenam
 }
 
 void com_codename1_impl_ios_IOSNative_screenshot__(CN1_THREAD_STATE_MULTI_ARG JAVA_OBJECT instanceObject) {
-    dispatch_sync(dispatch_get_main_queue(), ^{
+    dispatch_async(dispatch_get_main_queue(), ^{
         POOL_BEGIN();
-        UIView *view = [CodenameOne_GLViewController instance].view;
-        UIImage *img = cn1_captureView(view);
-        if (!img) {
-            POOL_END();
-            return;
-        }
+        @try {
+            UIView *view = [CodenameOne_GLViewController instance].view;
+            if (!view) {
+                NSLog(@"Screenshot failed: view is nil");
+                com_codename1_impl_ios_IOSImplementation_onScreenshot___byte_1ARRAY(CN1_THREAD_GET_STATE_PASS_ARG nil);
+                POOL_END();
+                return;
+            }
 
-        NSData *png = UIImagePNGRepresentation(img);
-        if (!png) {
-            POOL_END();
-            return;
-        }
+            UIImage *img = cn1_captureView(view);
+            if (!img) {
+                NSLog(@"Screenshot failed: cn1_captureView returned nil");
+                com_codename1_impl_ios_IOSImplementation_onScreenshot___byte_1ARRAY(CN1_THREAD_GET_STATE_PASS_ARG nil);
+                POOL_END();
+                return;
+            }
 
-        // Create Java byte[]
-        int len = (int)[png length];
-        JAVA_OBJECT byteArr = __NEW_ARRAY_JAVA_BYTE(CN1_THREAD_GET_STATE_PASS_ARG len);
+            NSData *png = UIImagePNGRepresentation(img);
+            if (!png) {
+                NSLog(@"Screenshot failed: UIImagePNGRepresentation returned nil");
+                com_codename1_impl_ios_IOSImplementation_onScreenshot___byte_1ARRAY(CN1_THREAD_GET_STATE_PASS_ARG nil);
+                POOL_END();
+                return;
+            }
 
-        memcpy((JAVA_ARRAY_BYTE*)((JAVA_ARRAY)byteArr)->data, (const jbyte*)[png bytes], len);
+            // Create Java byte[]
+            int len = (int)[png length];
+            NSLog(@"Screenshot captured: %d bytes", len);
+            JAVA_OBJECT byteArr = __NEW_ARRAY_JAVA_BYTE(CN1_THREAD_GET_STATE_PASS_ARG len);
 
-        com_codename1_impl_ios_IOSImplementation_onScreenshot___byte_1ARRAY(CN1_THREAD_GET_STATE_PASS_ARG byteArr);
+            if (!byteArr) {
+                NSLog(@"Screenshot failed: could not allocate Java byte array");
+                com_codename1_impl_ios_IOSImplementation_onScreenshot___byte_1ARRAY(CN1_THREAD_GET_STATE_PASS_ARG nil);
+                POOL_END();
+                return;
+            }
+
+            memcpy((JAVA_ARRAY_BYTE*)((JAVA_ARRAY)byteArr)->data, (const jbyte*)[png bytes], len);
+
+            com_codename1_impl_ios_IOSImplementation_onScreenshot___byte_1ARRAY(CN1_THREAD_GET_STATE_PASS_ARG byteArr);
+        } @catch (NSException *exception) {
+            NSLog(@"Screenshot failed with exception: %@", exception);
+            com_codename1_impl_ios_IOSImplementation_onScreenshot___byte_1ARRAY(CN1_THREAD_GET_STATE_PASS_ARG nil);
+        }
         POOL_END();
     });
 }

Ports/iOSPort/src/com/codename1/impl/ios/IOSImplementation.java

@@ -306,17 +306,39 @@ public void addCookie(Cookie c) {
     @Override
     public void screenshot(SuccessCallback<Image> callback) {
         screenshotCallback = callback;
-        nativeInstance.screenshot();
+        try {
+            nativeInstance.screenshot();
+        } catch(Exception e) {
+            Log.e(e);
+            if(screenshotCallback != null) {
+                screenshotCallback.onSucess(null);
+                screenshotCallback = null;
+            }
+        }
     }
 
     static void onScreenshot(final byte[] imageData) {
-        if(screenshotCallback != null) {
-            Display.getInstance().callSerially(new Runnable() {
-                @Override
-                public void run() {
-                    screenshotCallback.onSucess(EncodedImage.createImage(imageData));
-                }
-            });
+        try {
+            if(screenshotCallback != null) {
+                Display.getInstance().callSerially(new Runnable() {
+                    @Override
+                    public void run() {
+                        try {
+                            if(imageData != null) {
+                                screenshotCallback.onSucess(EncodedImage.createImage(imageData));
+                            } else {
+                                Log.e(new RuntimeException("Screenshot failed: imageData is null"));
+                                screenshotCallback.onSucess(null);
+                            }
+                        } catch(Exception e) {
+                            Log.e(e);
+                            screenshotCallback.onSucess(null);
+                        }
+                    }
+                });
+            }
+        } catch(Exception e) {
+            Log.e(e);
         }
     }