在两点之间画一条线 - 如何通过 UIView

Question

我正在尝试画一条连接两点的简单线。我想我在 drawLine 方法中得到了正确的代码。根本没有线条出现，我很确定这与我正在调用的视图和我想要绘制的视图有关。以下代码是我在代码中构建下一个视图的地方（数据来自 Web 服务）。视图创建得很好，所有按钮和对象都出现了。

我正在尝试向我正在创建的视图（下一步）动态添加行，但不知道如何完成。从我得到的错误（无效的上下文 0x0）看来，我做的事情有问题。试图在不存在的视图上显示。我怎样才能完成这项工作？任何建议将不胜感激。

我意识到传递视图可能不是正确的答案。我在这里处于反复试验阶段。

澄清一下：我在这里调用drawLine：

[nextView.view addSubview:next];

谢谢，

晒

-(void) drawView
{
CGRect rec;
CGFloat width = [UIScreen mainScreen].bounds.size.width;
CGFloat height = [UIScreen mainScreen].bounds.size.height;

UIView *next = [[UIView alloc]initWithFrame:CGRectMake(0, 0, height, width)];
next.backgroundColor = [UIColor whiteColor];
next.userInteractionEnabled = YES;
next.multipleTouchEnabled = YES;

nextView = [UIViewController alloc];
[nextView setTitle: as_objectDesc];

for (object in viewObjects)
{ // ratio based on Ipad 2 screen size conversion from the Datawindow size - alter to    support other device
    CGFloat objWidth = object.Width/3.83;
    CGFloat objHeight = object.Height/2.78;
    CGFloat objXPoint = object.positionX/3.83;
    CGFloat  objYPoint = object.positionY/2.78;

    if ([object.Shape isEqualToString:@"text"])
    {
        rec = CGRectMake(objXPoint, objYPoint, objWidth, objHeight);
        UILabel *myLabel = [[UILabel alloc] initWithFrame:rec];
        myLabel.backgroundColor = [UIColor clearColor];
        myLabel.text = object.objectTag;
        myLabel.lineBreakMode = NSLineBreakByWordWrapping;

        if ([object.description isEqualToString:@"Header"])
        {
            myLabel.font = [UIFont systemFontOfSize:20];
        }
        else
        {
            myLabel.font = [UIFont systemFontOfSize:10];
        }
        [next addSubview:myLabel];
    }
    else if ([object.Shape isEqualToString:@"line"])
    {
        **[self drawLine:nextView.view];**
    }
    else
    {
        UIButton *myButton = [UIButton buttonWithType:UIButtonTypeCustom];

    if ([object.Shape isEqualToString:@"ellipse"])
    {
        UIImage * buttonImage;
        if ([object.Color isEqualToString:@"255"])
        {
            buttonImage = [UIImage imageNamed:@"redBackground.png"];
        }
        else if ([object.Color isEqualToString:@"65535"])
        {
            buttonImage = [UIImage imageNamed:@"yellowBackground.png"];
        }
        else if ([object.Color isEqualToString:@"GRAY"])
        {
            buttonImage = [UIImage imageNamed:@"graybground.PNG"];
        }
        else if ([object.Color isEqualToString:@"BLACK"])
        {
            buttonImage = [UIImage imageNamed:@"BlackBackground.png"];
        }

        [myButton setBackgroundImage:buttonImage forState: UIControlStateNormal];

        objWidth = objHeight;
        rec = CGRectMake(objXPoint, objYPoint, objWidth, objHeight);

        myButton.frame = rec;
        myButton.clipsToBounds = YES;
        myButton.layer.cornerRadius = objWidth/2;


    }
    else
    {
        rec = CGRectMake(objXPoint, objYPoint, objWidth, objHeight);
        if ([object.Color isEqualToString:@"255"])
            myButton.backgroundColor = [UIColor redColor];
        else if ([object.Color isEqualToString:@"65535"])
            myButton.backgroundColor = [UIColor yellowColor];
        else if ([object.Color isEqualToString:@"GRAY"])
            myButton.backgroundColor = [UIColor grayColor];
        else if ([object.Color isEqualToString:@"BLACK"])
            myButton.backgroundColor = [UIColor blackColor];
    }


    [[myButton layer] setBorderWidth:1.0f];
    [[myButton layer] setBorderColor:[UIColor blackColor].CGColor];

    myButton.enabled = YES;
    myButton.accessibilityHint = object.objectTag;

    myButton.titleLabel.lineBreakMode = NSLineBreakByWordWrapping;
    myButton.titleLabel.textAlignment = NSTextAlignmentCenter;
    myButton.titleLabel.font = [UIFont systemFontOfSize:13];
    [myButton setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];


    [myButton addTarget:self action:@selector(btnClick:) forControlEvents:UIControlEventTouchUpInside];

        myButton.frame = rec;

        [myButton setTitle:object.description forState:UIControlStateNormal];

        // Check if an Empty Rectangle
        NSRange test =[myButton.accessibilityHint rangeOfString:@"r_"];
        if (test.location == 0)
        {
            [next sendSubviewToBack:myButton];
            [myButton setEnabled:NO];
        }

        [next addSubview:myButton];

    }

    UIPinchGestureRecognizer *twoFingerPinch = [[UIPinchGestureRecognizer alloc]
                                                 initWithTarget:self
                                                 action:@selector(twoFingerPinch:)]
                                                ;

    [[nextView view] addGestureRecognizer:twoFingerPinch];

    [next addSubview:activityIndicator];
    [next bringSubviewToFront:activityIndicator];

}
[nextView.view addSubview:next];

[self dismissViewControllerAnimated:NO completion:nil];
[self.navigationController pushViewController:nextView animated:NO];
 }

- (void)drawLine:(UIView *) view
{
    CGFloat x1 = object.positionX;
    CGFloat y1 = object.positionY;
    CGFloat x2 = object.positionX2;
    CGFloat y2 = object.positionY2;

    CGContextRef context = UIGraphicsGetCurrentContext();

    if ([object.Color isEqualToString:@"255"])
       CGContextSetStrokeColorWithColor(context, [UIColor redColor].CGColor);
    else if ([object.Color isEqualToString:@"65535"])
        CGContextSetStrokeColorWithColor(context, [UIColor yellowColor].CGColor); 
    else if ([object.Color isEqualToString:@"GRAY"])
        CGContextSetStrokeColorWithColor(context, [UIColor grayColor].CGColor);
    else if ([object.Color isEqualToString:@"BLACK"])
        CGContextSetStrokeColorWithColor(context, [UIColor blackColor].CGColor);

    CGContextSetLineWidth(context, 3.0);
    CGContextBeginPath(context);
    CGContextMoveToPoint(context, x1, y1);
    CGContextAddLineToPoint(context, x2, y2);
    CGContextStrokePath(context);
}

Answer 1

我最终想通了几天，并认为我会在这里分享。我可能在我的问题中添加了很多代码，这无助于将其简化给其他人（没有 cmets）。

这归结为当尝试绘制一条线时，您需要覆盖 UIView 子类的 DrawRect 方法，而不是像我那样覆盖 UIViewController。如果您从 UIViewController 调用 DrawRect 则不会引发错误，但它不会执行任何操作。我错过了那个小细节。

增加发现和解决这个问题的复杂性是我以编程方式创建所有这些，并且最初根本没有子类化 UIView。我最终在 NSMutablearray 中添加了所有点，并在创建新视图后重绘了以下类中的线条：

#import "draw.h"

@implementation draw
@synthesize lines;

- (id)initWithFrame:(CGRect)frame
{
   self = [super initWithFrame:frame];
if (self) 
{
// Initialization code
}
return self;
}

-(void)drawRect:(CGRect)rect
{

CGContextRef context = UIGraphicsGetCurrentContext();

for (line *myLine in lines)
{

    if ([myLine.color isEqualToString:@"255"])
             CGContextSetStrokeColorWithColor(context, [UIColor redColor].CGColor);
    else if ([myLine.color isEqualToString:@"65535"])
                CGContextSetStrokeColorWithColor(context, [UIColor yellowColor].CGColor);
    else if ([myLine.color isEqualToString:@"GRAY"])
                CGContextSetStrokeColorWithColor(context, [UIColor grayColor].CGColor);
    else if ([myLine.color isEqualToString:@"BLACK"])
                CGContextSetStrokeColorWithColor(context, [UIColor blackColor].CGColor);
    int setNew = myLine.Width/4;

    CGContextSetLineWidth(context, (CGFloat)setNew);
    CGContextBeginPath(context);
    CGContextMoveToPoint(context, myLine.x1, myLine.y1);
    CGContextAddLineToPoint(context, myLine.x2, myLine.y2);
    CGContextStrokePath(context);
}
}
@end