The introduction
UILabel is a highly visible UI control in daily development. This article will introduce how Apple designed the text information management of UILabel, and what pitfalls we will encounter in daily use.
Basic properties
UILabel *label = [[UILabel alloc] init];
NSLog(@ "% @", label.textColor);
NSLog(@ "% @", label.font);
NSLog(@ "% @", label.shadowColor);
NSLog(@ "% @", @(label.shadowOffset));
// How are these attributes stored?
<UIDynamicSystemColor: 0x6000031597c0; name = labelColor>
<UICTFont: 0x7ffdb9e08fb0> font-family: ".SFUI-Regular"; font-weight: normal; font-style: normal; font-size: 17.00pt
(null)
NSSize: {0.- 1}
Copy the codeHypothesis 1
Stored by the corresponding member variables of these attributes.
By printing the list of member variables of UILabel object, we find that there are no corresponding _textColor, _font, _shadowColor, _shadowOffset member variables. So where are these attributes stored?
After a closer look at the list, we find an interesting member variable: _content.
_content (_UILabelContent*): <_UILabelContent: 0x60000260cac0>
in UILabel:
_size (struct CGSize) : {0.0}
_highlightedColor (UIColor*) :nil
_numberOfLines (long) :1
_baselineInfo (struct?). : { firstBaseline (double) :0
lastBaseline (double) :0
referenceBounds (struct CGRect) : {{0.0}, {0.0}}
measuredNumberOfLines (long) :- 1
}
_previousBaselineOffsetFromBottom (double) :0
_previousFirstLineBaseline (double) :0
_minimumScaleFactor (double) :0
_content (_UILabelContent*): <_UILabelContent: 0x60000260cac0>
_synthesizedAttributedText (NSAttributedString*) :nil
_cachedSynthesizedTextAttributes (NSDictionary*) :nil
_fallbackColorsForUserInterfaceStyle (NSMutableDictionary*) :nil
_minimumFontSize (double) :0
_lineSpacing (long) :0
_layout (id) :nil
_scaledMetrics (_UILabelScaledMetrics*): nil
_intrinsicContentSizeCache (_UITextSizeCache*): nil
_contentsFormat (long) :0
_cuiCatalog (CUICatalog*): nil
_cuiStyleEffectConfiguration (CUIStyleEffectConfiguration*): <CUIStyleEffectConfiguration: 0x600000701f40>
_marqueeAnimations (NSMutableDictionary*) :nil
_marqueeMaskAnimations (NSMutableDictionary*) :nil
_textLabelFlags (struct?). : { highlighted (b1):NO
autosizeTextToFit (b1): NO
supportMultiLineShrinkToFit (b1): NO
autotrackTextToFit (b1): NO
baselineAdjustment (b2): 0
enabled (b1): YES
wordRoundingEnabled (b1): NO
explicitAlignment (b1): NO
enablesMarqueeWhenAncestorFocused (b1): NO
marqueeEnabled (b1): NO
marqueeRunable (b1): NO
marqueeRequired (b1): NO
usesExplicitPreferredMaxLayoutWidth (b1): NO
drawsDebugBaselines (b1): NO
explicitBaselineOffset (b1): NO
usesSimpleTextEffects (b1): NO
wantsUnderlineForAccessibilityButtonShapesEnabled (b1): NO
disableUpdateTextColorOnTraitCollectionChange (b1): NO
textAlignmentFollowsWritingDirection (b1): NO
textAlignmentMirrored (b1): NO
shortcutIntrinsicContentSize (b1): NO
multilineLabelRequiresCarefulMeasurement (b1): NO
noNeedsDisplayCheckForBaselineCalculationNeeded (b1): NO
overallWritingDirectionFollowsLayoutDirection (b1): NO
hyphenationFactorIgnoredIfURLsDetected (b1): NO
extendedAccessibilityAdjustments (b1): YES
canUseUILabelLayer (b1): YES
implementsDefaultAttributes (b1): NO
textColorFollowsTintColor (b1): NO
}
_adjustsFontForContentSizeCategory (BOOL) :NO
_preferredMaxLayoutWidth (double) :0
_multilineContextWidth (double) :0
_fontForShortcutBaselineCalculation (UIFont*) :nil
__visualStyle (_UILabelVisualStyle*): <_UILabelVisualStyle_iOS: 0x60000260c1f0>
in UIView:
_constraintsExceptingSubviewAutoresizingConstraints (NSMutableArray*) :nil
_cachedTraitCollection (UITraitCollection*).UITraitCollection: 0x600001f14b60>
_animationInfo (UIViewAnimationInfo*) :nil
_layer (CALayer*): <_UILabelLayer: 0x600000701ef0>
_layerRetained (CALayer*): <_UILabelLayer: 0x600000701ef0>
_gestureRecognizers (NSMutableArray*) :nil
_window (UIWindow*) :nil
_subviewCache (NSArray*) :nil
_viewDelegate (UIViewController*) :nil
_cachedScreenScale (double) :3
_layoutEngineWidth (double) :0
_viewFlags (struct?). : { userInteractionDisabled (b1):YES
implementsDrawRect (b1): YES
implementsDidScroll (b1): NO
implementsMouseTracking (b1): NO
implementsIntrinsicContentSize (b1): YES
hasBackgroundColor (b1): YES
hasBackgroundColorSystemColorName (b1): YES
hasInteractionTintColor (b1): NO
isOpaque (b1): YES
becomeFirstResponderWhenCapable (b1): NO
interceptMouseEvent (b1): NO
deallocating (b1): NO
isInUIViewDealloc (b1): NO
debugFlash (b1): NO
isAncestorOfFirstResponder (b1): NO
dontAutoresizeSubviews (b1): NO
autoresizeMask (b6): 0
patternBackground (b1): NO
fixedBackgroundPattern (b1): NO
dontAnimate (b1): NO
superLayerIsView (b1): NO
layerKitPatternDrawing (b1): NO
multipleTouchEnabled (b1): NO
exclusiveTouch (b1): NO
hasViewController (b1): NO
needsDidAppearOrDisappear (b1): NO
deliversTouchesForGesturesToSuperview (b1): YES
deliversButtonsForGesturesToSuperview (b1): YES
chargeEnabled (b1): NO
skipsSubviewEnumeration (b1): NO
needsDisplayOnBoundsChange (b1): NO
hasTiledLayer (b1): NO
hasLargeContent (b1): NO
traversalMark (b1): NO
appearanceIsInvalid (b1): NO
monitorsSubtree (b1): NO
hostsAutolayoutEngine (b1): NO
constraintsAreClean (b1): NO
subviewLayoutConstraintsAreClean (b1): NO
intrinsicContentSizeConstraintsAreClean (b1): NO
strictDescendantNeedsDoubleUpdateConstraints (b1): NO
strictDescendantNeedsDoubleUpdateConstraintsIsInvalid (b1): NO
determiningWidthForDoubleUpdateConstraints (b1): NO
inSecondConstraintsPass (b1): NO
potentiallyHasDanglyConstraints (b1): NO
doesNotTranslateAutoresizingMaskIntoConstraints (b1): NO
autolayoutIsClean (b1): NO
autolayoutBoundsAreClean (b1): NO
layoutFlushingDisabled (b1): NO
layingOutFromConstraints (b1): NO
wantsAutolayout (b1): NO
subviewWantsAutolayout (b1): NO
isApplyingValuesFromEngine (b1): NO
isResizingDueToParentResize (b1): NO
isInLayoutSubviewsOrVCCallback (b1): NO
isInAnimatedLayout (b1): NO
isSubviewUpdatingAutoresizingConstraints (b1): NO
isUpdatingConstraints (b1): NO
isReapplyingStillActiveBrokenConstraints (b1): NO
isHostingUpdateConstraintsPassDuringLayout (b1): NO
isRunningEngineLevelConstraintsPass (b1): NO
isUpdatingLayoutEngineHostConstraints (b1): NO
isExpectingToFlushPendingLayoutChangeNotifications (b1): NO
systemLayoutFittingSizeNeedsUpdate (b1): NO
systemLayoutFittingSizeNeedsUpdateInWholeSubtree (b1): NO
isCalculatingSystemLayoutFittingSize (b1): NO
suppressEncapsulationConstraints (b1): NO
isFetchingSizeForTAMIC_NOEngineHost (b1): NO
stayHiddenAwaitingReuse (b1): NO
stayHiddenAfterReuse (b1): NO
skippedLayoutWhileHiddenForReuse (b1): NO
isPendingHiddenForAnimation (b1): NO
hasMaskView (b1): NO
hasVisualAltitude (b1): NO
hasBackdropMaskViews (b1): NO
backdropMaskViewFlags (b5): 0
delaysTouchesForSystemGestures (b1): NO
subclassShouldDelayTouchForSystemGestures (b1): NO
hasMotionEffects (b1): NO
backdropOverlayMode (b2): 0
tintAdjustmentMode (b2): 0
isReferenceView (b1): NO
focusState (b2): 0
hasUserInterfaceIdiom (b1): NO
userInterfaceIdiom (b3): 0
ancestorDefinesTintColor (b1): NO
ancestorDefinesTintAdjustmentMode (b1): NO
ancestorIgnoresInvertColors (b1): NO
needsTraitCollectionDidChangePropagation (b1): NO
isRootOfTraitCollectionDidChangePropagation (b1): NO
implementsTraitCollectionForChildEnvironment (b1): NO
implementsBaselineOffsetsAtSize (b1): YES
coloredViewBounds (b1): NO
coloredAlignmentRects (b1): NO
preservesSuperviewMargins (b4): 0
insettingLayoutMarginsFromSafeArea (b4): 15
safeAreaInsetsFrozen (b1): NO
viewDelegateContentOverlayInsetsAreClean (b1): NO
hasGeometryObservers (b1): NO
observingGeometryChangesForSelfCount (b4): 0
hasTraitStorageList (b1): NO
cachedTraitCollectionIsValid (b1): YES
dontUpdateInferredLayoutMargins (b1): NO
areLayoutMarginsDirectional (b1): NO
implementsViewForBaselineLayout (b1): NO
tracksFocusedAncestors (b1): NO
hasLayoutArrangements (b1): NO
isHiddenManagedByLayoutArrangement (b1): NO
hasAddedFocusGuides (b1): NO
hasFocusSpeedBumpEdges (b1): NO
hasFocusableContentMargins (b1): NO
focusInteractionDisabled (b1): NO
shouldReverseLayoutDirection (b1): NO
cannotBeParentTraitEnvironment (b1): NO
hasTemplateLayoutView (b2): 0
ignoresTemplateLayoutView (b2): 0
needsContentsFormatUpdate (b1): YES
accessibilityIgnoresInvertColors (b1): NO
ignoresLayerTransformForSafeAreaInsets (b1): NO
accessibilityInterfaceStyleIntent (b2): 0
accessibilityResolvedInterfaceStyle (b2): 0
shouldArchiveUIAppearanceTags (b1): NO
wantsDeepColorDrawing (b1): YES
tagEnabled (b1): NO
chargeSet (b1): NO
ignoreBackdropViewsWhenHiding (b1): NO
areChildrenFocused (b1): NO
hasInteractionsArray (b1): NO
hasHitTestDirectionalInsets (b1): NO
hasLayoutDebuggingIdentifier (b1): NO
hasContentSizeNotificationToken (b1): NO
hasPresentationControllerToNotifyOnLayoutSubviews (b1): NO
semanticContentAttribute (b3): 0
hasDynamicBackgroundColor (b1): NO
hasLocalOverrideTraitCollection (b1): NO
forceEffectiveThemeDidChange (b1): NO
allowsHighContrastForBackgroundColor (b1): NO
hasPendingTraitStorageConstraints (b1): NO
hasEverBeenInAWindow (b1): NO
hasFocusGroupIdentifier (b2): 0
allowsSkippingLayout (b1): YES
}
_unsatisfiableConstraintsLoggingSuspensionCount (unsigned short): Value not representable, S
_pseudo_id (unsigned int) :35
_retainCount (long) :0
_draggingSourceDelegate (<_UIViewInternalDraggingSourceDelegate>*): nil
_tintAdjustmentDimmingCount (unsigned short): Value not representable, S
_layoutSubviewsCount (unsigned short): Value not representable, S
_imminentLayoutSubviewsCount (unsigned short): Value not representable, S
_countOfFocusedAncestorTrackingViewsInSubtree (unsigned short): Value not representable, S
_layoutMarginsGuide (UILayoutGuide*) :nil
_minXVariable (NSISVariable*) :nil
_minYVariable (NSISVariable*) :nil
_boundsWidthVariable (NSISVariable*) :nil
_boundsHeightVariable (NSISVariable*) :nil
_layoutEngine (NSISEngine*) :nil
_stashedLayoutVariableObservations (NSMapTable*) :nil
_internalConstraints (NSMutableArray*) :nil
_safeAreaLayoutGuide (UILayoutGuide*) :nil
_readableContentGuide (UILayoutGuide*) :nil
__preferedContentsFormat (long) :0
__lastNotifiedTraitCollection (UITraitCollection*).UITraitCollection: 0x600001f14b60>
__alignmentRectOriginCache (_UIViewLayoutEngineRelativeAlignmentRectOriginCache*): nil
_rawLayoutMargins (struct UIEdgeInsets) : {1.7976931348623157 e+308.1.7976931348623157 e+308.1.7976931348623157 e+308.1.7976931348623157 e+308}
_inferredLayoutMargins (struct UIEdgeInsets) : {1.7976931348623157 e+308.1.7976931348623157 e+308.1.7976931348623157 e+308.1.7976931348623157 e+308}
_safeAreaInsets (struct UIEdgeInsets) : {0.0.0.0}
in UIResponder:
_responderFlags (struct?). : { hasOverrideClient (b1):NO
hasOverrideHost (b1): NO
hasInputAssistantItem (b1): NO
suppressSoftwareKeyboard (b1): NO
}
in NSObject:
isa (Class): UILabel (isa, 0x7fff86d7b1c0)
Copy the codeSuppose 2
Stored via the member variable: _content.
(lldb) po [label valueForKey:@"content"]
<_UILabelContent:0x60000260cac0 attr={
NSColor = "<UIDynamicSystemColor: 0x6000031597c0; name = labelColor>";
NSFont = "
font-family: \".SFUI-Regular\"; font-weight: normal; font-style: normal; The font - size: 17.00 pt"
;
NSParagraphStyle = "Alignment 4, LineSpacing 0, ParagraphSpacing 0, ParagraphSpacingBefore 0, HeadIndent 0, TailIndent 0, FirstLineHeadIndent 0, LineHeight 0/0, LineHeightMultiple 0, LineBreakMode 4, Tabs (\n 28L,\n 56L,\n 84L,\n 112L,\n 140L,\n 168L,\n 196L,\n 224L,\n 252L,\n 280L,\n 308L,\n 336L\n), DefaultTabInterval 0, Blocks (null), Lists (null), BaseWritingDirection -1, HyphenationFactor 0, TighteningForTruncation NO, HeaderLevel 0 LineBreakStrategy 65535";
NSShadow = "NSShadow {0, -1} color = {(null)}"; } >Copy the codeWe print the _content value via KVC and see that these attributes are indeed stored in the _content member variable.
NSLog(@”%@”, label.textColor);
<UIDynamicSystemColor: 0x6000031597c0; name = labelColor>
NSColor and label.textColor refer to the same object in _content.
NSColor = “<UIDynamicSystemColor: 0x6000031597c0; name = labelColor>”;
In addition, other attributes of UILabel such as textAlignment and lineBreakMode are also stored in the NSParagraphStyle of _content.
validation
We can also verify that our guess is correct by assigning values to these attributes and looking at the value of _content.
- (void)viewDidLoad {
[super viewDidLoad];
UILabel *label = [[UILabel alloc] init];
label.textColor = [UIColor redColor];
label.font = [UIFont systemFontOfSize:40.0];
label.shadowColor = [UIColor redColor];
label.shadowOffset = CGSizeZero;
NSLog(@ "% @", label.textColor);
NSLog(@ "% @", label.font);
NSLog(@ "% @", label.shadowColor);
NSLog(@ "% @", @(label.shadowOffset));
NSLog(@ "% @", [label valueForKey:@"content"]);
}
/ / output
UIExtendedSRGBColorSpace 1 0 0 1
<UICTFont: 0x7fea0e8096c0> font-family: ".SFUI-Regular"; font-weight: normal; font-style: normal; font-size: 40.00pt
UIExtendedSRGBColorSpace 1 0 0 1
NSSize: {0.0}
<_UILabelContent:0x6000025fc6c0 attr={
NSColor = "UIExtendedSRGBColorSpace 1 0 0 1";
NSFont = "
font-family: \".SFUI-Regular\"; font-weight: normal; font-style: normal; The font - size: 40.00 pt"
;
NSParagraphStyle = "Alignment 4, LineSpacing 0, ParagraphSpacing 0, ParagraphSpacingBefore 0, HeadIndent 0, TailIndent 0, FirstLineHeadIndent 0, LineHeight 0/0, LineHeightMultiple 0, LineBreakMode 4, Tabs (\n 28L,\n 56L,\n 84L,\n 112L,\n 140L,\n 168L,\n 196L,\n 224L,\n 252L,\n 280L,\n 308L,\n 336L\n), DefaultTabInterval 0, Blocks (null), Lists (null), BaseWritingDirection -1, HyphenationFactor 0, TighteningForTruncation NO, HeaderLevel 0 LineBreakStrategy 65535";
NSShadow = "NSShadow {0, 0} color = {UIExtendedSRGBColorSpace 1 0 0 1}"; } >Copy the codeThe text property
So we see that the _content of UILabel after initialization stores the _UILabelContent object. What happens if we assign through text?
- (void)viewDidLoad {
[super viewDidLoad];
UILabel *label = [[UILabel alloc] init];
label.text = @"ByteDance";
}
(lldb) po [label valueForKey:@"content"]
<_UILabelStringContent:0x600003573780 len=9 ByteDance attr={
NSColor = "<UIDynamicSystemColor: 0x60000206a980; name = labelColor>";
NSFont = "
font-family: \".SFUI-Regular\"; font-weight: normal; font-style: normal; The font - size: 17.00 pt"
;
NSParagraphStyle = "Alignment 4, LineSpacing 0, ParagraphSpacing 0, ParagraphSpacingBefore 0, HeadIndent 0, TailIndent 0, FirstLineHeadIndent 0, LineHeight 0/0, LineHeightMultiple 0, LineBreakMode 4, Tabs (\n 28L,\n 56L,\n 84L,\n 112L,\n 140L,\n 168L,\n 196L,\n 224L,\n 252L,\n 280L,\n 308L,\n 336L\n), DefaultTabInterval 0, Blocks (null), Lists (null), BaseWritingDirection -1, HyphenationFactor 0, TighteningForTruncation NO, HeaderLevel 0 LineBreakStrategy 65535";
NSShadow = "NSShadow {0, -1} color = {(null)}"; } >Copy the codeWe see that _content stores the _UILabelStringContent object, which records our string @”ByteDance”, length 9, and property information.
In other words, the string that we put in text ends up being rich text by UILabel.
AttributedText properties
The text property is relatively simple, with few potholes. But attributedText is a lot more complicated, and if you mix it with text, sometimes you set text, sometimes you set attributedText, it’s even more complicated.
Question 1
How does UILabel display when we don’t add any attributes to the attributedText?
UILabel *label = [[UILabel alloc] init];
NSString *text = @"ByteDance";
label.attributedText = [[NSAttributedString alloc] initWithString:text];
Copy the code
Let’s look at the _content property.
UILabel *label = [[UILabel alloc] init];
NSString *text = @"ByteDance";
label.attributedText = [[NSAttributedString alloc] initWithString:text];
NSLog(@ "% @", [label valueForKey:@"content"]);
/ / output
<_UILabelAttributedStringContent:0x600003b88840 attributed len=9 ByteDance attr={
NSColor = "<UIDynamicSystemColor: 0x600002ed7900; name = labelColor>";
NSFont = "
font-family: \".SFUI-Regular\"; font-weight: normal; font-style: normal; The font - size: 17.00 pt"
;
NSParagraphStyle = "Alignment 4, LineSpacing 0, ParagraphSpacing 0, ParagraphSpacingBefore 0, HeadIndent 0, TailIndent 0, FirstLineHeadIndent 0, LineHeight 0/0, LineHeightMultiple 0, LineBreakMode 4, Tabs (\n 28L,\n 56L,\n 84L,\n 112L,\n 140L,\n 168L,\n 196L,\n 224L,\n 252L,\n 280L,\n 308L,\n 336L\n), DefaultTabInterval 0, Blocks (null), Lists (null), BaseWritingDirection -1, HyphenationFactor 0, TighteningForTruncation NO, HeaderLevel 0 LineBreakStrategy 65535";
NSShadow = "NSShadow {0, -1} color = {(null)}"; } >Copy the codeYou can see the _content properties, storage is _UILabelAttributedStringContent object, including a rich text, length of 9 and attribute information, attribute information are the default values.
So what does rich text store?
(lldb) po [0x600003b88840 valueForKey:@"attributedString"]
ByteDance{
}
Copy the codeWhen we print it out, it’s just a string, no attribute information.
That is, when UILabel presents, it adds default attributes to strings that have no attributes.
Question 2
What happens if we just add attributes to the attributedText part?
UILabel *label = [[UILabel alloc] init];
NSString *text = @"ByteDance";
NSMutableAttributedString *attStr = [[NSMutableAttributedString alloc] initWithString:text];
[attStr addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:NSMakeRange(0.1)];
label.attributedText = attStr;
id content = [label valueForKey:@"content"];
NSLog(@ "% @", content);
id attributedString = [content valueForKey:@"attributedString"];
NSLog(@ "% @", attributedString);
/ / output
<_UILabelAttributedStringContent:0x600000048200 attributed len=9 ByteDance attr={
NSColor = "<UIDynamicSystemColor: 0x600001522500; name = labelColor>";
NSFont = "
font-family: \".SFUI-Regular\"; font-weight: normal; font-style: normal; The font - size: 17.00 pt"
;
NSParagraphStyle = "Alignment 4, LineSpacing 0, ParagraphSpacing 0, ParagraphSpacingBefore 0, HeadIndent 0, TailIndent 0, FirstLineHeadIndent 0, LineHeight 0/0, LineHeightMultiple 0, LineBreakMode 4, Tabs (\n 28L,\n 56L,\n 84L,\n 112L,\n 140L,\n 168L,\n 196L,\n 224L,\n 252L,\n 280L,\n 308L,\n 336L\n), DefaultTabInterval 0, Blocks (null), Lists (null), BaseWritingDirection -1, HyphenationFactor 0, TighteningForTruncation NO, HeaderLevel 0 LineBreakStrategy 65535";
NSShadow = "NSShadow {0, -1} color = {(null)}";
}>
B{
NSColor = "UIExtendedSRGBColorSpace 1 0 0 1";
}yteDance{
}
Copy the code
We can see that the part with added attributes uses the added attributes, while the part without added attributes still uses the default attributes.
In other words, there are two factors that determine the final display:
- The attribute of the attributedText itself (highest priority)
- If no properties are set, properties in UILabel are used
Pit point 1
Again, what is the color of label.textColor?
UILabel *label = [[UILabel alloc] init];
NSString *text = @"ByteDance";
NSMutableAttributedString *attStr = [[NSMutableAttributedString alloc] initWithString:text];
[attStr addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:NSMakeRange(0.1)];
label.attributedText = attStr;
NSLog(@ "% @", label.textColor);
Copy the codeAnswer: redColor
UIExtendedSRGBColorSpace 1 0 0 1
So if YOU change range to NSMakeRange(1, 1) and ask: What is the color of label.textColor?
UILabel *label = [[UILabel alloc] init];
NSString *text = @"ByteDance";
NSMutableAttributedString *attStr = [[NSMutableAttributedString alloc] initWithString:text];
[attStr addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:NSMakeRange(1.1)];
label.attributedText = attStr;
NSLog(@ "% @", label.textColor);
Copy the codeAnswer: Default color
<UIDynamicSystemColor: 0x600002dc1ec0; name = labelColor>
To explore the
Again, let’s take the textColor property as an example. We found system call defaultValueForAttribute: view the source code to get the value, if there is a value is returned the value; Otherwise, _defaultColor is returned.
We further defaultValueForAttribute:. We find that if the length of the text is greater than or equal to one, and the 0th bit of the attributedString is configured, it returns that value; Otherwise, the relevant configuration values are taken from the ATTR dictionary.
This also explains how UILabel takes text attributes for rendering.
conclusion
In daily use, we need to pay attention to the usage scenario when using UILabel configuration attributes, especially after assigning the value to the attributedText attribute, the attribute acquisition will be different, which requires special attention.
Question 3
Question 2: If we only add attributes to the attributedText part, what happens if we add attributes to the whole thing?
Look _UILabelAttributedStringContent stored in content and in question 2, only the rich text attributes are added to the whole.
UILabel *label = [[UILabel alloc] init];
NSString *text = @"ByteDance";
NSMutableAttributedString *attStr = [[NSMutableAttributedString alloc] initWithString:text];
[attStr addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:NSMakeRange(0, attStr.length)];
label.attributedText = attStr;
id content = [label valueForKey:@"content"];
NSLog(@ "% @", content);
id attributedString = [content valueForKey:@"attributedString"];
NSLog(@ "% @", attributedString);
/ / output
<_UILabelAttributedStringContent:0x600000da26e0 attributed len=9 ByteDance attr={
NSColor = "<UIDynamicSystemColor: 0x6000018cc840; name = labelColor>";
NSFont = "
font-family: \".SFUI-Regular\"; font-weight: normal; font-style: normal; The font - size: 17.00 pt"
;
NSParagraphStyle = "Alignment 4, LineSpacing 0, ParagraphSpacing 0, ParagraphSpacingBefore 0, HeadIndent 0, TailIndent 0, FirstLineHeadIndent 0, LineHeight 0/0, LineHeightMultiple 0, LineBreakMode 4, Tabs (\n 28L,\n 56L,\n 84L,\n 112L,\n 140L,\n 168L,\n 196L,\n 224L,\n 252L,\n 280L,\n 308L,\n 336L\n), DefaultTabInterval 0, Blocks (null), Lists (null), BaseWritingDirection -1, HyphenationFactor 0, TighteningForTruncation NO, HeaderLevel 0 LineBreakStrategy 65535";
NSShadow = "NSShadow {0, -1} color = {(null)}";
}>
ByteDance{
NSColor = "UIExtendedSRGBColorSpace 1 0 0 1";
}
Copy the codePit point 2
What happens if we assign a value to text after assigning an attribute to attributedText?
We first experiment with just adding attributes to the attributedText part.
UILabel *label = [[UILabel alloc] init];
NSString *text = @"ByteDance";
NSMutableAttributedString *attStr = [[NSMutableAttributedString alloc] initWithString:text];
[attStr addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:NSMakeRange(0.1)];
label.attributedText = attStr;
label.text = text;
Copy the code- Option 1
- Option 2
I don’t think you have any questions. The answer is choice 1.
Experiment 2
If you add attributes to the whole attributedText, now what do you choose?
[attStr addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:NSMakeRange(0, attStr.length)];
Copy the codeAnd the answer is choice 2.
Not only that, but printing _content also finds that the default attr property has changed to redColor.
That is, instead of just adding some attributes to the attributedText, the default color value of the UILabel object has been replaced.
id content = [label valueForKey:@"content"];
NSLog(@ "% @", content);
/ / output
<_UILabelStringContent:0x60000378dfe0 len=9 ByteDance attr={
NSColor = "UIExtendedSRGBColorSpace 1 0 0 1";
NSFont = "
font-family: \".SFUI-Regular\"; font-weight: normal; font-style: normal; The font - size: 17.00 pt"
;
NSParagraphStyle = "Alignment 4, LineSpacing 0, ParagraphSpacing 0, ParagraphSpacingBefore 0, HeadIndent 0, TailIndent 0, FirstLineHeadIndent 0, LineHeight 0/0, LineHeightMultiple 0, LineBreakMode 4, Tabs (\n 28L,\n 56L,\n 84L,\n 112L,\n 140L,\n 168L,\n 196L,\n 224L,\n 252L,\n 280L,\n 308L,\n 336L\n), DefaultTabInterval 0, Blocks (null), Lists (null), BaseWritingDirection -1, HyphenationFactor 0, TighteningForTruncation NO, HeaderLevel 0 LineBreakStrategy 65535";
NSShadow = "NSShadow {0, -1} color = {(null)}"; } >Copy the codeExperiment 3
Before assigning a value to the text, clear the attributedText. Now what’s your choice?
UILabel *label = [[UILabel alloc] init];
NSString *text = @"ByteDance";
NSMutableAttributedString *attStr = [[NSMutableAttributedString alloc] initWithString:text];
[attStr addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:NSMakeRange(0, attStr.length)];
label.attributedText = attStr;
label.attributedText = nil;
label.text = text;
Copy the codeAnd the answer is choice 1. Printing _content also shows that the default attr property has not changed.
<_UILabelStringContent:0x600001c4fd20 len=9 ByteDance attr={
NSColor = "<UIDynamicSystemColor: 0x6000009710c0; name = labelColor>";
NSFont = "
font-family: \".SFUI-Regular\"; font-weight: normal; font-style: normal; The font - size: 17.00 pt"
;
NSParagraphStyle = "Alignment 4, LineSpacing 0, ParagraphSpacing 0, ParagraphSpacingBefore 0, HeadIndent 0, TailIndent 0, FirstLineHeadIndent 0, LineHeight 0/0, LineHeightMultiple 0, LineBreakMode 4, Tabs (\n 28L,\n 56L,\n 84L,\n 112L,\n 140L,\n 168L,\n 196L,\n 224L,\n 252L,\n 280L,\n 308L,\n 336L\n), DefaultTabInterval 0, Blocks (null), Lists (null), BaseWritingDirection -1, HyphenationFactor 0, TighteningForTruncation NO, HeaderLevel 0 LineBreakStrategy 65535";
NSShadow = "NSShadow {0, -1} color = {(null)}"; } >Copy the codeTo explore the
From the above experiment, we found that the problem was related to setting the text property.
Through the NSAttributedString attributesAtIndex: longestEffectiveRange: inRange: If longestEffectiveRange and length are the same length and there are values in the dictionary, then we do a series of operations and compare the new dictionary if it is different from attr. And when we finally initialize, we’re going to use this dictionary to initialize the entire _content.
So, when you set an attribute for the entire rich text, you replace the default attribute of the UILabel object.
conclusion
Before assigning a value to the text attribute, clear the value in the attributedText attribute to avoid the possibility of changing the default color value of the UILabel object.
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