Text: send metrics after rendering (iOS)

Summary: This adds a callback for <Text> to get metrics about the rendered text. It's divided by line but that could be changed to "fragments" (which makes more sense for multi-lingual). Right now by line is convenient as you frequently want to know where the first and last line end (though we could make this work with fragments I suppose).

Reviewed By: shergin

Differential Revision: D9440914

fbshipit-source-id: bb011bb7a52438380d3f604ffe7019b98c18d978

Libraries/Text/Text.js

@@ -64,6 +64,12 @@ const viewConfig = {
     adjustsFontSizeToFit: true,
     minimumFontScale: true,
     textBreakStrategy: true,
+    onTextLayout: true,
+  },
+  directEventTypes: {
+    topTextLayout: {
+      registrationName: 'onTextLayout',
+    },
   },
   uiViewClassName: 'RCTText',
 };

Libraries/Text/Text/RCTTextShadowView.h

@@ -19,6 +19,7 @@ NS_ASSUME_NONNULL_BEGIN
 @property (nonatomic, assign) NSLineBreakMode lineBreakMode;
 @property (nonatomic, assign) BOOL adjustsFontSizeToFit;
 @property (nonatomic, assign) CGFloat minimumFontScale;
+@property (nonatomic, copy) RCTDirectEventBlock onTextLayout;
 
 - (void)uiManagerWillPerformMounting;
 

Libraries/Text/Text/RCTTextShadowView.m

@@ -304,6 +304,35 @@ - (void)layoutSubviewsWithContext:(RCTLayoutContext)layoutContext
       [shadowView layoutWithMetrics:localLayoutMetrics layoutContext:localLayoutContext];
     }
   ];
+
+
+  if (_onTextLayout) {
+    NSMutableArray *lineData = [NSMutableArray new];
+    [layoutManager
+     enumerateLineFragmentsForGlyphRange:glyphRange
+     usingBlock:^(CGRect overallRect, CGRect usedRect, NSTextContainer * _Nonnull usedTextContainer, NSRange lineGlyphRange, BOOL * _Nonnull stop) {
+       NSRange range = [layoutManager characterRangeForGlyphRange:lineGlyphRange actualGlyphRange:nil];
+       NSString *renderedString = [textStorage.string substringWithRange:range];
+       UIFont *font = [[textStorage attributedSubstringFromRange:range] attribute:NSFontAttributeName atIndex:0 effectiveRange:nil];
+       [lineData addObject:
+        @{
+          @"text": renderedString,
+          @"x": @(usedRect.origin.x),
+          @"y": @(usedRect.origin.y),
+          @"width": @(usedRect.size.width),
+          @"height": @(usedRect.size.height),
+          @"descender": @(-font.descender),
+          @"capHeight": @(font.capHeight),
+          @"ascender": @(font.ascender),
+          @"xHeight": @(font.xHeight),
+          }];
+     }];
+    NSDictionary *payload =
+    @{
+      @"lines": lineData,
+      };
+    _onTextLayout(payload);
+  }
 }
 
 - (CGFloat)lastBaselineForSize:(CGSize)size

Libraries/Text/Text/RCTTextView.h

@@ -5,6 +5,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+#import <React/RCTComponent.h>
+
 #import <UIKit/UIKit.h>
 
 NS_ASSUME_NONNULL_BEGIN

Libraries/Text/Text/RCTTextViewManager.m

@@ -34,6 +34,8 @@ @implementation RCTTextViewManager
 RCT_REMAP_SHADOW_PROPERTY(adjustsFontSizeToFit, adjustsFontSizeToFit, BOOL)
 RCT_REMAP_SHADOW_PROPERTY(minimumFontScale, minimumFontScale, CGFloat)
 
+RCT_EXPORT_SHADOW_PROPERTY(onTextLayout, RCTDirectEventBlock)
+
 RCT_EXPORT_VIEW_PROPERTY(selectable, BOOL)
 
 - (void)setBridge:(RCTBridge *)bridge