iOS 自定义滑杆实现-优快云博客

本文链接：https://blog.youkuaiyun.com/ChasingDreamsCoder/article/details/53074677

本文介绍了如何在iOS开发中创建自定义滑杆，展示了一个实现滑杆功能的实例，并提供了核心代码，帮助读者理解并应用到自己的项目中。

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先让我们看看效果：

主要实现的代码：

UIImage *thumbWithLevel(float aLevel)
{
    float INSET_AMT = 1.5f;
    CGRect baseRect = CGRectMake(0, 0, 40, 100);
    CGRect thumbRect = CGRectMake(0, 40, 40, 20);
    
    UIGraphicsBeginImageContext(baseRect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    
    [[UIColor darkGrayColor] setFill];
    CGContextAddRect(context, CGRectInset(thumbRect, INSET_AMT, INSET_AMT));
    CGContextFillPath(context);
    
    [[UIColor whiteColor] setStroke];
    CGContextSetLineWidth(context, 2);
    CGContextAddRect(context, CGRectInset(thumbRect, 2 * INSET_AMT, 2 * INSET_AMT));
    CGRect ellipseRect = CGRectMake(0, 0, 40, 40);
    [[UIColor colorWithWhite:aLevel alpha:1] setFill];
    CGContextAddEllipseInRect(context, ellipseRect);
    CGContextFillPath(context);
    
    NSString *numString = [NSString stringWithFormat:@"%0.2f",aLevel];
    UIColor *textColor = (aLevel > 0.5) ? [UIColor blackColor] : [UIColor whiteColor];
    UIFont *font = [UIFont fontWithName:@"Georgia" size:15];
    NSMutableParagraphStyle *style = [[NSMutableParagraphStyle alloc] init];
    style.lineBreakMode = NSLineBreakByCharWrapping;
    style.alignment = NSTextAlignmentCenter;
    NSDictionary *attr = @{NSFontAttributeName:font,NSParagraphStyleAttributeName:style,NSForegroundColorAttributeName:textColor};
    [numString drawInRect:CGRectInset(ellipseRect, 0, 6) withAttributes:attr];
    
    [[UIColor grayColor] setStroke];
    CGContextSetLineWidth(context, 3);
    CGContextAddEllipseInRect(context, CGRectInset(ellipseRect, 2, 2));
    CGContextStrokePath(context);
    
    UIImage *theImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    return  theImage;
}

在这里我们通过context的方法将图片画出了，对于性能有点要求，但是现在应该不在乎这点性能了

- (void)updateThumb
{
    if ((self.value < 0.98) && (ABS(self.value - previousValue) < 0.1f)) {
        return;
    }
    
    UIImage *customImg = thumbWithLevel(self.value);
    [self setThumbImage:customImg forState:UIControlStateHighlighted];
    previousValue = self.value;
}

通过滑块的值来使上面的值进行变化，更加的直观

   [self setThumbImage:simpleThumb() forState:UIControlStateNormal];
        [self addTarget:self action:@selector(startDrag:) forControlEvents:UIControlEventTouchDown];
        [self addTarget:self action:@selector(updateThumb) forControlEvents:UIControlEventValueChanged];
        [self addTarget:self action:@selector(endDrag:) forControlEvents:UIControlEventTouchUpOutside | UIControlEventTouchUpInside];

对于不同的状态来进行不同的操作，让滑杆的用户体验度更加的完整