我刚刚开始使用 Core Plot，并且为了测试，将 CPTGraphHostingView 嵌入到一个简单的自定义 View Controller 中，绘制来自 Core Data fetchRequest 的值(这是一个绘制每日​​饮食卡路里摄入量的应用程序).

代码大部分是从教程中粘贴的 here .

问题是将 View Controller 插入 View (它嵌入在导航 Controller 中)时，UI 卡住了大约两秒钟。这是在设备 (iPhone 4S) 上运行时的情况。

Instruments 中的分析显示主线程被 [CPTAxis layoutSublayers] 和 [CPTLayer drawInContext] 阻塞。

滞后不是由于数据集过大:它目前恰好包含两个点。该图非常简单，看起来像这样:

View Controller 的完整实现:​​

接口(interface):

//
//  ICCaloriesGraphController.h
//  iCalories
//
//  Created by David Fearon on 22/08/2013.
//  Copyright (c) 2013 David Fearon. All rights reserved.
//

#import <UIKit/UIKit.h>
#import "CorePlot-CocoaTouch.h"
#import "ICDatabaseBrain.h"
#import "Day.h"
#import "CalorieEntry.h"

@interface ICCaloriesGraphController : UIViewController<CPTPlotDataSource, NSFetchedResultsControllerDelegate>
@property (weak, nonatomic) IBOutlet CPTGraphHostingView *graphHostingView;
@property (nonatomic, retain)ICDatabaseBrain* sharedDatabaseBrain;
@property (nonatomic, retain)NSFetchedResultsController* resultsController;

@end

实现:

//
//  ICCaloriesGraphController.m
//  iCalories
//
//  Created by David Fearon on 22/08/2013.
//  Copyright (c) 2013 David Fearon. All rights reserved.
//

#import "ICCaloriesGraphController.h"

@interface ICCaloriesGraphController ()

@property int numberOfRecordsForPlot;
@property float maxDailyCaloriesInDataset;
@property NSArray* days;

@end

@implementation ICCaloriesGraphController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.sharedDatabaseBrain = [ICDatabaseBrain sharedDatabaseBrain];
    self.resultsController = self.sharedDatabaseBrain.fetchDaysResultsController;

    self.days = [self.resultsController fetchedObjects];
    self.numberOfRecordsForPlot = [self.days count];

    [self updateMaxDailyCaloriesInDataset];

    // Create a CPTGraph object and add to hostView
    CPTGraph* graph = [[CPTXYGraph alloc] initWithFrame:self.graphHostingView.bounds];
    self.graphHostingView.hostedGraph = graph;

    // Get the (default) plotspace from the graph so we can set its x/y ranges
    CPTXYPlotSpace *plotSpace = (CPTXYPlotSpace *) self.graphHostingView.hostedGraph.defaultPlotSpace;

    // Note that these CPTPlotRange are defined by START and LENGTH (not START and END) !!
    [plotSpace setYRange: [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat( 0 ) length:CPTDecimalFromFloat( self.maxDailyCaloriesInDataset )]];
    [plotSpace setXRange: [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat( 0 ) length:CPTDecimalFromFloat( self.numberOfRecordsForPlot )]];

    // Create the plot (we do not define actual x/y values yet, these will be supplied by the datasource...)
    CPTScatterPlot* plot = [[CPTScatterPlot alloc] initWithFrame:CGRectZero];

    // Let's keep it simple and let this class act as datasource (therefore we implement <CPTPlotDataSource>)
    plot.dataSource = self;

    // Finally, add the created plot to the default plot space of the CPTGraph object we created before
    [self.graphHostingView.hostedGraph addPlot:plot toPlotSpace:self.graphHostingView.hostedGraph.defaultPlotSpace];

}

-(void)viewWillAppear:(BOOL)animated{

    [super viewWillAppear:animated];

}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


-(NSUInteger)numberOfRecordsForPlot:(CPTPlot *)plotnumberOfRecords {
    return self.numberOfRecordsForPlot;
}


-(void)updateMaxDailyCaloriesInDataset{

    if (self.numberOfRecordsForPlot == 0){
        self.maxDailyCaloriesInDataset = 0;
        return;
    }

    int max = 0;

    for (Day* day in self.days) {

        //count the calories in the day:
        int calorieSum = 0;
        for (CalorieEntry* calorieEntry in [day.calorieEntries allObjects]) {
            calorieSum += calorieEntry.calories.intValue;
        }

        if(calorieSum > max) max = calorieSum;

    }

    self.maxDailyCaloriesInDataset = max;

}


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

    if (self.numberOfRecordsForPlot == 0){
        return 0;
    }

    if(fieldEnum == CPTScatterPlotFieldY){

        Day* day = [self.days objectAtIndex:index];

        //count the calories in the day:
        int calorieSum = 0;
        for (CalorieEntry* calorieEntry in [day.calorieEntries allObjects]) {
            calorieSum += calorieEntry.calories.intValue;
        }

        return [NSNumber numberWithInt:calorieSum];
        //TODO: Set range for y axis

    }

    if(fieldEnum == CPTScatterPlotFieldX){
        return [NSNumber numberWithInt: index];
    }else{
        NSLog(@"fieldEnum was neither CPTScatterPlotFieldY or CPTScatterPlotFieldX in numberForPlot:");
        return 0;
    }

}

@end

滞后绝对与 Core Data 代码无关；一切正常。谷歌搜索只会显示庞大数据集的问题，而不是只有两点的问题。显然我在 Core Plot 代码上做了一些根本性的错误，但我真的看不出是什么。

有人能发现问题吗？

最佳答案

maxDailyCaloriesInDataset 大吗？默认的轴标签策略将刻度线和标签沿轴分开一个单位。如果 yRange 很大，就会产生很多重叠的标签，这会非常慢。根据您应用的要求，增加 majorIntervalLength 以减少标签数量，或者更改标签政策。 CPTAxisLabelingPolicyAutomatic 和 CPTAxisLabelingPolicyEqualDivisions 将是不错的选择。

关于ios - 加载包含 Core Plot 图的 View Controller 时延迟过大，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/18404887/