ios - 加载包含 Core Plot 图的 View Controller 时延迟过大
<p><p>我刚开始使用 Core Plot，为了测试，在一个简单的自定义 ViewController 中嵌入了一个 <code>CPTGraphHostingView</code>，绘制来自 Core Data fetchRequest 的值(这是一个绘制每天膳食卡路里摄入量的应用程序)。</p>
<p>代码大部分是从教程 <a href="http://www.mobdevel.com/?p=96" rel="noreferrer noopener nofollow">here</a> 中粘贴的.</p>
<p>问题是当将 ViewController 插入 View 时 UI 卡住了大约两秒钟(它嵌入在导航 Controller 中)。这是在设备 (iPhone 4S) 上运行时。</p>
<p>Instruments 中的分析显示主线程被 <code></code> 和 <code></code> 阻塞。</p>
<p>延迟不是由于数据集过大:它目前正好包含两个点。该图<em>非常</em>简单，如下所示:</p>
<p> <img src="/image/MHOou.png" alt="enter image description here"/> </p>
<p> ViewController 的完整实现:</p>
<p>界面:</p>
<pre><code>//
//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
</code></pre>
<p>实现:</p>
<pre><code>//
//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 = ;
if (self) {
// Custom initialization
}
return self;
}
- (void)viewDidLoad
{
;
self.sharedDatabaseBrain = ;
self.resultsController = self.sharedDatabaseBrain.fetchDaysResultsController;
self.days = ;
self.numberOfRecordsForPlot = ;
;
// Create a CPTGraph object and add to hostView
CPTGraph* graph = [ 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) !!
];
];
// Create the plot (we do not define actual x/y values yet, these will be supplied by the datasource...)
CPTScatterPlot* plot = [ 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
;
}
-(void)viewWillAppear:(BOOL)animated{
;
}
- (void)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 ) {
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 = ;
//count the calories in the day:
int calorieSum = 0;
for (CalorieEntry* calorieEntry in ) {
calorieSum += calorieEntry.calories.intValue;
}
return ;
//TODO: Set range for y axis
}
if(fieldEnum == CPTScatterPlotFieldX){
return ;
}else{
NSLog(@"fieldEnum was neither CPTScatterPlotFieldY or CPTScatterPlotFieldX in numberForPlot:");
return 0;
}
}
@end
</code></pre>
<p>延迟绝对与 Core Data 代码无关；一切正常。谷歌搜索只会显示大型数据集的问题，而不是只有两点的问题。显然，我对核心情节代码做了一些根本性的错误，但真的看不出是什么。</p>
<p>请问有人能发现问题吗？</p></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><p><code>maxDailyCaloriesInDataset</code> 大吗？默认轴标签策略将刻度标记和标签沿轴分开一个单位。如果 <code>yRange</code> 很大，这会创建很多重叠的标签，这可能会非常慢。根据您的应用程序的要求，增加 <code>majorIntervalLength</code> 使其不会制作这么多标签，或者更改标签策略。 <code>CPTAxisLabelingPolicyAutomatic</code> 和 <code>CPTAxisLabelingPolicyEqualDivisions</code> 会是不错的选择。</p></p>
<p style="font-size: 20px;">关于ios - 加载包含 Core Plot 图的 ViewController 时延迟过大，我们在Stack Overflow上找到一个类似的问题：
<a href="https://stackoverflow.com/questions/18404887/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/18404887/
</a>
</p>
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