Question

我正在尝试绘制一个根据滑块值上下移动的图形。我的图表是在属于自定义类GraphView的视图中绘制的。项目有一个ViewController，滑块调用方法moveLine。这有一个属性endXPoint，我已设置为： endXPoint = mySlider.value

我的问题是我不知道如何从我的GraphView的drawRect方法中引用这个值。

我尝试在ViewController中创建对GraphView的引用并在那里设置属性，但它不起作用：
GraphView * myGraphView =（GraphView *）self.view;
myGraphView.endXPoint = mySlider.value;

Answer 1

您必须为GraphView类设置一个属性：

@interface GraphView : UIView
@property float endXPoint;

然后从ViewController中设置GraphView变量，如：

[myGraphView setendXPoint: [mySlider value]];
[myGraphView setNeedsDisplay];

最后一行要求GraphView更新View，调用drawRect方法。在drawRect方法中，您可以直接使用endXPoint，因为它是一个类属性。

这是正确的版本：

//ViewController.h

#import <UIKit/UIKit.h> 
#import "GraphView.h" //import headers in the header file

@interface ViewController : UIViewController  

@property (strong, nonatomic) IBOutlet UISlider *mySlider;  
@property (strong, nonatomic) IBOutlet UILabel *myLabel;  
@property (strong, nonatomic) IBOutlet GraphView *myGraphView; //Connect this with the IB

- (IBAction)moveLine:(id)sender; 
- (IBAction)setLabelText:(id)sender;  
@end  

//ViewController.m

#import "ViewController.h"   

@implementation ViewController  
@synthesize mySlider;  
@synthesize myLabel;  
@synthesize myGraphView;



- (IBAction)moveLine:(id)sender {  
    [myGraphView setendXPoint:[mySlider value]];  
    [myGraphView setNeedsDisplay];  
}  

@end 

//GraphView.h 

#import <UIKit/UIKit.h>  

@interface GraphView : UIView  
@property float endXPoint;  


@end

//GraphView.m  

#import "GraphView.h"   

@implementation GraphView  
@synthesize endXPoint;  


- (void)drawRect:(CGRect)rect  
{

    CGContextRef ctx = UIGraphicsGetCurrentContext(); //get the graphics context  
    CGContextSetRGBStrokeColor(ctx, 1.0, 0, 0, 1);   
    CGContextMoveToPoint(ctx, 0, 0);  
    //add a line from 0,0 to the point 100,100;   
    CGContextAddLineToPoint( ctx, endXPoint,100);  
    //"stroke" the path  
    CGContextStrokePath(ctx);  
}  


@end

Xcode如何从自定义类中检索滑块值

1 个答案: