如何使用 coreplot 实时绘制图表？

Question

我正在尝试使用 coreplot 在图表（CPScatterPlot）上绘制声音的分贝值。但问题是我得到的图表有一条垂直于 Y 轴的线，并且它相对于分贝值的变化在 Y 轴上上下移动。我需要绘制这样的图表。

这是我的代码： `

    -(void) generateDataSamples
    {

     samples = [[NSMutableArray alloc]initWithCapacity:NUM_SAMPLES];

     for (int i=0; i < NUM_SAMPLES; i++) 

        {
            // peakVal is a variable that holds the decibel value   
             NSDictionary *sample = [NSDictionary dictionaryWithObjectsAndKeys:                         
             [NSNumber numberWithDouble:peakVal],Y_VAL,nil];
             [samples addObject:sample];
            } 

    }

-(NSUInteger)numberOfRecordsForPlot:(CPPlot *)plot; 
{
   return [samples count];
}

-(NSNumber *)numberForPlot:(CPPlot *)plot field:(NSUInteger)fieldEnum 
               recordIndex:(NSUInteger)index{

 NSDictionary *sample = [samples objectAtIndex:index];
 NSDecimalNumber *num = [NSDecimalNumber zero];
    if (fieldEnum == CPScatterPlotFieldX) 
    {
        num = (NSDecimalNumber *) [NSDecimalNumber numberWithInt:index + 1];
    }
    else if (fieldEnum == CPScatterPlotFieldY)
    {
    return [sample valueForKey:Y_VAL];
    }
    return num; 
}

那么，我应该怎样做才能得到如上图所示的图表呢？请帮助我，我是新来的。

还有一点，如上图所示，Y 轴标签放置在绘图区域内，这是如何做到的？

这是我的完整代码，请建议修改：

#import "MicBlowViewController.h"
#import "SecondVC.h"
#define DBOFFSET -74.0
#define START_POINT 0.0
#define END_POINT 100.0
#define NUM_SAMPLES 200.0
#define MAX_PEAK 100.0

#define X_VAL @"X_VAL"
#define Y_VAL @"Y_VAL"
#define S_VAL @"S_VAL"


@implementation MicBlowViewController
@synthesize avgLabel, peakLabel,absValue,pageControl;


-(void)reloadData
{
    if(!graph)
    {
        //setting graph
        double xAxisStart = START_POINT;
        double xAxisLength = END_POINT - START_POINT;
        double maxY = 100;//[[samples valueForKeyPath:@"@max.Y_VAL"] doubleValue];
        double yAxisStart = START_POINT;
        double yAxisLength = maxY+3;
        xVal=START_POINT+0.1;
        hostingView = [[CPGraphHostingView alloc] initWithFrame:CGRectMake(0, 79, 320, 361)];
        [self.view  addSubview:hostingView];
        graph = [[CPXYGraph alloc] initWithFrame:CGRectMake(0, 79, 320, 361)];
        hostingView.hostedGraph = graph;

        CPTheme *theme = [CPTheme themeNamed:kCPDarkGradientTheme];
        [graph applyTheme:theme];
        graph.paddingTop = 0.0;
        graph.paddingBottom = 0.0;
        graph.paddingLeft = 0.0;
        graph.paddingRight = 0.0;
        [[graph defaultPlotSpace] setAllowsUserInteraction:TRUE];
        CPXYAxisSet *axisSet = (CPXYAxisSet *)graph.axisSet;
        axisSet.yAxis.labelOffset=0.1;
        CPXYAxis *x = axisSet.xAxis;
        x.majorIntervalLength = CPDecimalFromDouble(10.0);
        x.orthogonalCoordinateDecimal = CPDecimalFromInteger(0);
        x.minorTicksPerInterval = 1;

        CPXYAxis *y = axisSet.yAxis;

        y.majorIntervalLength=CPDecimalFromDouble(10.0);
        y.orthogonalCoordinateDecimal = CPDecimalFromInteger(0);
        y.minorTicksPerInterval = 1;
        y.tickDirection = CPSignPositive;
        y.labelAlignment = CPAlignmentLeft;
        y.alternatingBandFills = [NSArray arrayWithObjects:[[CPColor whiteColor] colorWithAlphaComponent:0.1], [NSNull null], nil];
        CPXYPlotSpace *plotSpace = (CPXYPlotSpace *)graph.defaultPlotSpace;
        plotSpace.xRange = [CPPlotRange plotRangeWithLocation:CPDecimalFromDouble(xAxisStart)
                                                       length:CPDecimalFromDouble(xAxisLength)];

        plotSpace.yRange = [CPPlotRange plotRangeWithLocation:CPDecimalFromDouble(yAxisStart)
                                                       length:CPDecimalFromDouble(yAxisLength)];    

        CPScatterPlot *dataSourceLinePlot = [[CPScatterPlot alloc] init];
        dataSourceLinePlot.dataSource = self;
        //[dataSourceLinePlot insertDataAtIndex:[samplesY count]-1 numberOfRecords:1];

        CPMutableLineStyle *lineStyle = [[dataSourceLinePlot.dataLineStyle mutableCopy] autorelease];
        lineStyle.lineWidth = 2.f;
        lineStyle.lineColor = [CPColor cyanColor];
        dataSourceLinePlot.dataLineStyle = lineStyle;

        [graph addPlot:dataSourceLinePlot];

        [dataSourceLinePlot release];
        [graph release];
        [hostingView release];
    }
}

- (void)generateData
{

       // if (plotData == nil) {
        NSMutableArray *contentArray = [NSMutableArray array];

        for (NSUInteger i = 0; i < 200; i++) {
            //double test = (double)[peakLabel.text doubleValue];
            absValue.text =[NSString stringWithFormat:@"%.2f",peakVal];
            id x = [NSDecimalNumber numberWithDouble:1.0 + i ];
            id y = [NSDecimalNumber numberWithDouble:peakVal * rand()/(double)RAND_MAX + 0.05];
            [contentArray addObject:[NSMutableDictionary dictionaryWithObjectsAndKeys:x, @"x", y, @"y", nil]];
        }
        plotData = [contentArray retain];
        //}

}
-(NSUInteger)numberOfRecordsForPlot:(CPPlot *)plot ;
{
    return [plotData count];
}

-(NSNumber *)numberForPlot:(CPPlot *)plot field:(NSUInteger)fieldEnum 
               recordIndex:(NSUInteger)index;
{
    NSNumber *num = [[plotData objectAtIndex:index] valueForKey:(fieldEnum == CPScatterPlotFieldX ? @"x" : @"y")];

    if (fieldEnum == CPScatterPlotFieldY) {
        num = [NSNumber numberWithDouble:[num doubleValue]];

    }
    return num;
}

- (void)viewDidLoad {
    [super viewDidLoad];
    pageControl = [[UIPageControl alloc]init];
    [pageControl addTarget:self action:@selector(changePage) forControlEvents:UIControlEventValueChanged];
    samplesY = [[NSMutableArray alloc]init];
    //checking for sound
    NSURL *url = [NSURL fileURLWithPath:@"/dev/null"];

    NSDictionary *settings = [NSDictionary dictionaryWithObjectsAndKeys:
                              [NSNumber numberWithFloat: 44100.0],                 AVSampleRateKey,
                              [NSNumber numberWithInt: kAudioFormatAppleLossless], AVFormatIDKey,
                              [NSNumber numberWithInt: 1],                         AVNumberOfChannelsKey,
                              [NSNumber numberWithInt: AVAudioQualityMax],         AVEncoderAudioQualityKey,
                              nil];

    NSError *error;
    recorder = [[AVAudioRecorder alloc] initWithURL:url settings:settings error:&error];

    if (recorder) {
        [recorder prepareToRecord];
        recorder.meteringEnabled = YES;
        [recorder record];
        levelTimer = [NSTimer scheduledTimerWithTimeInterval: 0.03 target: self selector: @selector(levelTimerCallback:) userInfo: nil repeats: YES];
    }// else
    //NSLog([error description]);   
}


- (void)levelTimerCallback:(NSTimer *)timer {
    // getting decibel values....
    [recorder updateMeters];

    const double ALPHA = 0.05;
    double peakPowerForChannel = pow(10, (0.05 * [recorder peakPowerForChannel:0]));

    lowPassResults = ALPHA * peakPowerForChannel + (1.0 - ALPHA) * lowPassResults;  

    NSLog(@"Average input: %f Peak input: %f Low pass results: %f",
          [recorder averagePowerForChannel:0], [recorder peakPowerForChannel:0], lowPassResults);
    peakval=fabs([recorder peakPowerForChannel:0]);
    double avgval=fabs([recorder averagePowerForChannel:0]);
    peakVal=MAX_PEAK - peakval;
    avgVal=MAX_PEAK - avgval;
    NSLog(@"First: %.2f",peakVal);

    avgLabel.text=[NSString stringWithFormat:@"%.2f",avgVal];
    peakLabel.text=[NSString stringWithFormat:@"%.2f",peakVal];
    if (lowPassResults < 0.95)
        NSLog(@"Mic blow detected: %d",lowPassResults);

    [self generateData];

    [self reloadData];

}

- (IBAction) changePage:(id)sender{
    SecondVC *vc = [[SecondVC alloc]init];
    vc.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
    [self presentModalViewController:vc animated:YES];
    [vc release];
}

- (void)dealloc {
    [peakLabel.text release];
    [avgLabel.text release];
    [samples release];
    [levelTimer release];
    [recorder release];
    [super dealloc];
}

@end

Answer 1

看起来您对每个数据点都使用相同的 peakVal。检查 -generateDataSamples 方法并确保您在 samples 数组中存储了正确的值。如果数组中已有数据，则可以完全跳过该方法，只需按 -numberForPlot:field:recordIndex: 中的索引进行查找即可。

另外，检查绘图空间上的 xRange 和 yRange 以确保它们适合您的数据。请记住，绘图范围类似于 NSRange — 它们是使用起始位置和长度而不是起始值和结束值创建的。

要将标签移动到 y 轴右侧，请使用 yAxis.tickDirection = CPTSignPositive;。

根据评论进行编辑

不要每次获取新数据时都调用 -generateDataSamples。相反，请将新值添加到 samples 数组中。不要忘记在第一次使用数组之前初始化它。

NSDictionary *sample = [NSDictionary dictionaryWithObjectsAndKeys:                         
    [NSNumber numberWithDouble:peakVal],Y_VAL,nil];
[samples addObject:sample];

数据进入数组后，告诉 Core Plot 仅加载新点。这比每次更新时重新加载所有数据要快。

[myScatterPlot insertDataAtIndex:(samples.count - 1)
                 numberOfRecords:1];

如果您不需要保留图表中的所有历史记录，可以使用 CPTPlot 方法 -deleteDataInIndexRange: 删除旧数据点。不要忘记从 samples 数组中删除相应的点。