在Xcode中为钛画线不透明

Question

我是新来的xCode，我有一个问题。我正在为我的Ipad做一个应用程序。我想突出显示文字，但是我无法设置我的线条的不透明度。我搜索了互联网，但我没有找到任何有关它的信息。现在我使用这个drawImage.alpha = lineOpacity;但是这并不好，我之前画的所有东西都会得到那种不透明性。我只想在新的绘制中完成alpha。现在就在此处使用此代码：

//here I init the opacity 
    -(id)init 
    { 
     if (self = [super init]) 
     { 
      strokeWidth = 5; 
      strokeColor = CGColorRetain([[TiUtils colorValue:@"#000"] _color].CGColor); 
      lineOpacity = 1; 
     } 
     return self; 
    } 
    - (void)dealloc 
{ 
    RELEASE_TO_NIL(drawImage); 
    CGColorRelease(strokeColor); 
    [super dealloc]; 
} 

- (void)frameSizeChanged:(CGRect)frame bounds:(CGRect)bounds 
{ 
    [super frameSizeChanged:frame bounds:bounds]; 
    if (drawImage!=nil) 
    { 
     [drawImage setFrame:bounds]; 
    } 
} 

    //here I add a call 
    - (void)setLineOpacity_:(id)alpha 
    { 
     lineOpacity = [TiUtils floatValue:alpha]; 
    } 

    //here I want to set the opacity 
    - (void)drawAt:(CGPoint)currentPoint 
    { 
     UIView *view = [self imageView]; 
     UIGraphicsBeginImageContext(view.frame.size); 
     [drawImage.image drawInRect:CGRectMake(0, 0, view.frame.size.width, view.frame.size.height)]; 
     CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound); 
     CGContextSetLineWidth(UIGraphicsGetCurrentContext(), strokeWidth); 
     CGContextSetStrokeColorWithColor(UIGraphicsGetCurrentContext(), strokeColor); 
     CGContextBeginPath(UIGraphicsGetCurrentContext()); 
     CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y); 
     CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y); 
     CGContextStrokePath(UIGraphicsGetCurrentContext()); 
     //here i want to set the alpha, but everything I draw before get also the new alpha. 
     //I just want the alpha to be done on the new draw 
     drawImage.alpha = lineOpacity; 
     drawImage.image = UIGraphicsGetImageFromCurrentImageContext(); 
     UIGraphicsEndImageContext(); 
     lastPoint = currentPoint; 
    } 

我希望有人能帮助我。提前致谢。

编辑：我用这个图纸：

- (UIImageView*)imageView 
{ 
    if (drawImage==nil) 
    { 
     drawImage = [[UIImageView alloc] initWithImage:nil]; 
     drawImage.frame = [self bounds]; 
     [self addSubview:drawImage]; 
    } 
    return drawImage; 
} 

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event 
{ 
    [super touchesBegan:touches withEvent:event]; 

    UITouch *touch = [touches anyObject]; 
    lastPoint = [touch locationInView:[self imageView]]; 
    lastPoint.y -= 20; 
} 

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event 
{ 
    [super touchesMoved:touches withEvent:event]; 

    UITouch *touch = [touches anyObject]; 
    CGPoint currentPoint = [touch locationInView:[self imageView]]; 
    currentPoint.y -= 20; 
    [self drawAt:currentPoint]; 
} 

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event 
{ 
    [super touchesEnded:touches withEvent:event]; 
    [self drawAt:lastPoint]; 
} 

#pragma mark Public APIs 

- (void)setStrokeWidth_:(id)width 
{ 
    strokeWidth = [TiUtils floatValue:width]; 
} 

- (void)setStrokeColor_:(id)value 
{ 
    CGColorRelease(strokeColor); 
    TiColor *color = [TiUtils colorValue:value]; 
    strokeColor = [color _color].CGColor; 
    CGColorRetain(strokeColor); 
} 

- (void)setLineOpacity_:(id)alpha 
{ 
    lineOpacity = [TiUtils floatValue:alpha]; 
} 

我真的想办法，找出它不会工作，寻觅了很长一段时间就可以了。

Answer 1

可以做出的UIColor并获得CGColorRef从这样的：

strokeColor = CGColorRetain([UIColor colorWithRed:1.0f green:1.0f blue:0.0f alpha:0.5f].CGColor); 

Answer 2

的不透明度被设为与笔划颜色的α值（在本例0.5）：

strokeColor = CGColorCreateGenericRGB(1.0f, 1.0f, 0.0f, 0.5f);