Question

我有一个ViewController类和一个View类。 ViewController有一个UIScrollView，View有一个UITableView，都是UIScrollViewDelegate的委托。

View和ViewController都使用scrollViewDidScroll:委托方法，并且两者都有相同的代码。这显然是一个重复，所以我想解决这个问题。

问题是我不知道怎么做。

我无法将功能提取到基类中，我也不认为我可以有一个单独的类来实现该方法，我可以使用它的实例（它可以在Android中使用，但不能在iOS中使用）。我正在考虑使用积木，但不知道它们是如何在这里工作的。

该方法本身在ViewController / View的UI上执行一些更改;这是它的身体：

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {

    float multiplierYAnimationStop = [Utilities getFloatValueFromPlistFile:@"layout_values" forDictionaryKey:@"scroll_background_y_stop_multiplier"];
    float currentScrollOffsetY = scrollView.contentOffset.y;

    // No case for further back than the bottom of the screen (lower than 0)
    // and if it's higher than where it should stop, keep it at that point
    if (currentScrollOffsetY > screenHeight * multiplierYAnimationStop) {

        currentScrollOffsetY = screenHeight * multiplierYAnimationStop;
    }

    // Scale the background
    float newBackgroundScale = 1 - currentScrollOffsetY / screenHeight;

    if (newBackgroundScale < 0.75f) {

        newBackgroundScale = 0.75f;
    }

    [self scaleBackgroundToNewScale:newBackgroundScale];

    // Move the UILabel with the title and the Button
    float newLabelCenterY = originalLabelTitleCentreY - currentScrollOffsetY;
    float newButtonCenterY = originalButtonDownArrowCentreY - currentScrollOffsetY;
    self.labelHeadline.center = CGPointMake(self.labelHeadline.center.x, newLabelCenterY);
    self.buttonDownArrow.center = CGPointMake(self.buttonDownArrow.center.x, newButtonCenterY);

    // Blur the UILabel with the title and the Button
    float newHeadlineAlpha = 1 - currentScrollOffsetY / 100.0f;

    if (newHeadlineAlpha < 0.0f) {

        newHeadlineAlpha = 0.0f;
    }

    [self.labelHeadline setAlpha:newHeadlineAlpha];
    [self.buttonDownArrow setAlpha:newHeadlineAlpha];

    if (newHeadlineAlpha < 0.95f) {

        [self.buttonDownArrow setEnabled:NO];
    }
    else {

        [self.buttonDownArrow setEnabled:YES];
    }

    // Set the new alpha for the background overlay
    // (no bigger than scroll_overlay_max_opacity, should be scroll_overlay_max_opacity once the offset hits the stop point)
    float maxOpacity = [Utilities getFloatValueFromPlistFile:@"layout_values" forDictionaryKey:@"scroll_overlay_max_opacity"];
    float subtractionFactor = 1.0f - maxOpacity;

    float newOverlayAlpha = currentScrollOffsetY / screenHeight / multiplierYAnimationStop - subtractionFactor;

    if (newOverlayAlpha > maxOpacity) {

        newOverlayAlpha = maxOpacity;
    }

    [self.viewOverlay setAlpha:newOverlayAlpha];

    // If set, move the background vertically on scroll
    if ([Utilities getBoolValueFromPlistFile:@"layout_values" forDictionaryKey:@"is_scroll_background_movable"]) {

        if (newBackgroundScale == 0.75f) {

            self.imageBackground.center = CGPointMake(self.imageBackground.center.x, self.imageBackground.center.y - (currentScrollOffsetY - 0.25f * screenHeight));
        }
    }
}

Answer 1

创建一个封装所需内容的函数，并将任何所需的变量（可能包括self）传递给它。

如果对象之间有更多重复的逻辑，则可以将它们组合到一个策略对象中，该对象具有一个实例（而不是继承）。基本上这将是你的代表的委托（这很好）。或者如果你有一组相关的共享函数，你可以使它们成为某些策略类的类方法。但如果它只是这样的一个方法，那么函数就可以了。

Answer 2

我之前只提供了以下相关代码，以便您了解如何使用单独的课程来完成此目标。

@interface MyScrollDelegate : NSObject <UIScrollViewDelegate>
@property (weak) id originalSelf;
@end

@interface MyViewController
@property (strong) MyScrollDelegate *aScrollDelegate;
@end

@interface MyView
@property (strong) MyScrollDelegate *aScrollDelegate;
@end

@implementation MyViewController
- (void)loadView {
  self.aScrollDelegate.originalSelf = self;
  myScrollView.setDelegate = self.aScrollDelegate;
}
@end

@implementation MyView
- (instancetype)init {
  self.aScrollDelegate.originalSelf = self;
  myScrollView.setDelegate = self.aScrollDelegate;
}
@end

从代理方法的2个实现中删除代码重复

2 个答案: