核心绘图CPTextLayer：文本与背景图像对齐作为背景颜色

Question

我写下面的代码来显示条形图注释。显示注释但出现意外的对齐/位置。 CPTextLayer的文本显示在框架的左上角。我试图在中心展示它。我已经使用CPTextLayer的背景图像作为背景颜色。请有过代码 - 一看（symbolTextAnnotation是在界面decleared一个CPLayerAnnotation对象）

-(void)barPlot:(CPBarPlot *)plot barWasSelectedAtRecordIndex:(NSUInteger)index 
{ 
    CPXYGraph* graph = (CPXYGraph*)plot.graph; 
    NSNumber *value = [self numberForPlot:plot field:CPBarPlotFieldBarTip recordIndex:index]; 

    if (symbolTextAnnotation) { 
     [graph.plotAreaFrame.plotArea removeAnnotation:symbolTextAnnotation]; 
     symbolTextAnnotation = nil; 
    } 

    // Setup a style for the annotation 
    CPMutableTextStyle *hitAnnotationTextStyle = [CPMutableTextStyle textStyle]; 
    hitAnnotationTextStyle.color = [CPColor whiteColor]; 
    hitAnnotationTextStyle.fontSize = 9.0f; 
    hitAnnotationTextStyle.fontName = @"Helvetica-Bold"; 


    // Determine point of symbol in plot coordinates 
    NSNumber *x = [NSNumber numberWithInt:index+1]; 
    NSNumber *y = [NSNumber numberWithInt:0]; 

    NSArray *anchorPoint = [NSArray arrayWithObjects:y, x, nil]; 

    // Add annotation 
    // First make a string for the y value 
    NSNumberFormatter *formatter = [[[NSNumberFormatter alloc] init] autorelease]; 
    [formatter setMaximumFractionDigits:2]; 
    NSString *yString = [formatter stringFromNumber:value]; 

    // Now add the annotation to the plot area 
    UIImage *annotationBG = [UIImage imageNamed:@"annotation-bg.png"]; 
    CPTextLayer *textLayer = [[[CPTextLayer alloc] initWithText:yString style:hitAnnotationTextStyle] autorelease]; 

    textLayer.backgroundColor = [UIColor colorWithPatternImage:annotationBG].CGColor; 
    textLayer.frame = CGRectMake(0, 0, annotationBG.size.width, annotationBG.size.height); 


    symbolTextAnnotation = [[CPPlotSpaceAnnotation alloc] initWithPlotSpace:plot.plotSpace anchorPlotPoint:anchorPoint]; 
    symbolTextAnnotation.contentLayer = textLayer; 
    symbolTextAnnotation.displacement = CGPointMake(-18.0f, 3.0f); 

    [graph.plotAreaFrame.plotArea addAnnotation:symbolTextAnnotation];  
} 

Answer 1

CPTextLayer尺寸本身的文本的大小。设置文本后调整大小会导致绘图问题。你可以制作另一个CPLayer，设置你​​的背景，让你的CPTextLayer成为一个子图层，然后根据需要定位它。

displacement属性与contentAnchorPoint属性一起使用来定位注释。 contentAnchorPoint是您的内容层的核心动画锚点。位移是该点与注释的anchorPlotPoint的像素偏移量。例如，如果要将注释集中在anchorPlotPoint中，请将contentAnchorPoint设置为CGPointMake(0.5, 0.5)，并将位移设置为CGPointZero。