accessing method of custom view in view controller - objective-c

Question

I am a new-be in Objective C. Here I want to ask a simple question.
I have created a view controller in storyboard, and customized its view with a subclass of UIView.
However, I don't know how to call methods of the view in my view controller. Can anyone help? All I want to do is to call drawLine:pointStore in ChartViewController.m from chartView.m
Here are some of my codes.
ChartViewController.h
#import <UIKit/UIKit.h>
#class chartView;
#interface ChartViewController : UIViewController{
chartView *chart_view;
}
ChartViewController.m
- (void)viewDidLoad
{
[super viewDidLoad];
NSMutableDictionary *pointStore = [[NSMutableDictionary alloc]init];
NSNumber *initX;
NSNumber *initY;
NSMutableDictionary *variableSet = [[NSMutableDictionary alloc]init];
for(initX = [NSNumber numberWithDouble:-10.0f];initX.floatValue<=10.0f;initX = [NSNumber numberWithDouble:(initX.floatValue+0.5f)] )
{
[variableSet setValue:initX forKey:#"x"];
initY = [NSNumber numberWithDouble:[self.brain performOperation:equationOfChart withVariable:variableSet]];
[pointStore setObject:initX forKey:initY];
}
[chart_view drawLine:pointStore];
}
chartView.h
#interface chartView : UIView
#property (nonatomic, strong) NSString *equation;
-(void) getEquation:(NSString *)Equation;
-(void) drawLine:(NSMutableDictionary *)pointsStore;
#end
chartView.m
-(void)drawLine:(NSMutableDictionary *)pointsStore{
CGContextRef c = UIGraphicsGetCurrentContext();
CGFloat red[4] = {1.0f, 0.0f, 0.0f, 1.0f};
CGContextSetStrokeColor(c, red);
CGContextBeginPath(c);
CGContextStrokePath(c);
for(NSNumber *ax = [NSNumber numberWithDouble:-10.0f];ax.floatValue<10.0f;){
float ay = [[pointsStore objectForKey:ax]doubleValue];
ax = [NSNumber numberWithDouble:(ax.floatValue+0.5f)];
int by = [[pointsStore objectForKey:ax]doubleValue];
[self.class line:ax.floatValue y:ay x2:(ax.floatValue+0.5) y2:by];
}
}

Answer 1

ChartViewController.h
#import <UIKit/UIKit.h>
#class chartView;
#interface ChartViewController : UIViewController
#property (string, nonatomic) chartView *chart_view;
#end
chartView.m
- (void)viewDidLoad
{
[super viewDidLoad];
...
// Don't forget to alloc and init
self.chart_view = [[chartView alloc] init];
[self.chart_view drawLine:pointStore];
}

Answer 2

You should check that the instance of chart_view is created and assigned. Probably you have nil in that poiner.
How to do this -- depend on the way you have chosen to create the view: in Interface Builder or dynamically, in code.