Objective c 如何使用drawRect在现有视图中绘制？

我正在做一个GPS跟踪应用程序。每次接收到纬度/经度时，它都会将其转换为（x，y）坐标，并调用

drawRect

在两个（x，y）对之间绘制一条线

然而，drawRect方法只是在绘制新内容之前清除所有旧内容。如何使drawRect在现有画布上绘制新事物？提前谢谢

这是我的viewController.h

我的绘图类，UIView的子类

---

你说的“旧内容”到底是什么意思？如果要从GPS数据绘制直线，则必须在每次实施drawRect时绘制所有点。

UIView没有画布模型。如果要保留画布，应创建

CGLayer

或

CGBitmapContext

并在其上绘制。然后在你的视野中画出来

我会为

CGLayerRef

创建一个ivar，然后

drawRect:

看起来像这样（未测试）：

只要想清除画布，只需

self.cgLayer=NULL

setCgLayer:

应该是这样的：

- (void)setCgLayer:(CGLayerRef)aLayer {
    CGLayerRetain(aLayer);
    CGLayerRelease(cgLayer_);
    cgLayer_ = aLayer;
}

---

第一次GPS获得lat/long，该功能使用该数据绘制一条线并显示它。但下一次GPS获得新数据时，旧的线就会消失，并画出一条新的线。那不是我想要的。我希望旧的线存在，并画出一条新的线。你每次都得画所有的线。例如，您需要将所有坐标存储在NSMutableArray中，并在im drawRect中绘制整个数组的内容。@Kin，请确保将注释作为注释而不是答案发布。主持人已删除您的非答案答案。CGLayerRef将是视图上的实例变量（ivar）。它应该有一个类似RouteTrackView的名称，而不是“routetrack”。永远不要使用箭头符号

self->locationX

，除非你真的知道自己在做什么（这几乎是不正确的）。这应该是

self.locationX

，您应该包括

@synthetic locationX

创建访问器。

#import "simpleDrawViewController.h"
#import "routetrack.h"

@implementation simpleDrawViewController
@synthesize locationManager,btn,routeroute;

- (IBAction) gpsValueChanged{

            [routeroute setLocationX:longNew setLocationY:latNew 
             oldLocation:longOld oldLocationY:latOld ];
            [routeroute setNeedsDisplay];

}


- (void)viewDidLoad {
    [super viewDidLoad];

    if (nil == locationManager)
    locationManager = [[CLLocationManager alloc] init];

    locationManager.delegate = self;
    locationManager.desiredAccuracy = kCLLocationAccuracyBest;  

    [locationManager startUpdatingLocation];
}



- (void)didReceiveMemoryWarning {
    // Releases the view if it doesn't have a superview.
    [super didReceiveMemoryWarning];    
    // Release any cached data, images, etc that aren't in use.
}

- (void)viewDidUnload {
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}


- (void) locationManager:(CLLocationManager *)manager 
         didUpdateToLocation:(CLLocation *)newLocation 
         fromLocation:(CLLocation *)oldLocation
{   
         if (oldLocation) {

            latOld=oldLocation.coordinate.latitude;
            longOld=oldLocation.coordinate.longitude;
            latNew=newLocation.coordinate.latitude;
            longNew=newLocation.coordinate.longitude;   
}

        else {
            latOld=53.3834;
            longOld=-6.5876;
            latNew=53.3835;
            longNew=-6.5877;
        }

        [self gpsValueChanged];

}



- (void) locationManager:(CLLocationManager *)manager didFailwithError:
(NSError *)error
{
    if([error code] == kCLErrorDenied)
        [locationManager stopUpdatingLocation];

    NSLog(@"location manger failed");
}




- (void)dealloc {
    [locationManager release];
    [super dealloc];
}

@end

#import "routetrack.h"


@implementation routetrack



- (void) setLocationX:(float) loX setLocationY:(float) loY 
         oldLocation:(float) oldX oldLocationY:(float) oldY {


    self->locationX = loX;
    self->locationY = loY;
    self->oldLoX = oldX;
    self->oldLoY = oldY;

    scaleX= 36365.484375;
    scaleY= 99988.593750;
    maxLat= 53.3834;
    maxLog= -6.5976;

    drawX = locationX;
    drawY = locationY;

    tempX=(maxLog - drawX) * scaleX;
    tempY=(maxLat   - drawY) * scaleY;

    lastX = (int) tempX;
    lastY = (int) tempY;

    drawX = oldLoX;
    drawY = oldLoY;

    tempX=(maxLog - drawX) * scaleX;
    tempY=(maxLat   - drawY) * scaleY;

    startX = (int) tempX;
    startY = (int) tempY;


}

- (id)initWithFrame:(CGRect)frame {

    self = [super initWithFrame:frame];
    if (self) {
    }
    return self;

}


- (void)drawRect:(CGRect)rect {

        int firstPointX = self->startX; 
    int firstPointY = self->startY;
    int lastPointX = self->lastX;
    int lastPointY = self->lastY;

    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetRGBStrokeColor(context, 1.0, 0.0, 0.0, 1.0);
    CGContextSetLineWidth(context, 2.0);

    CGContextMoveToPoint(context, firstPointX, firstPointY);

    CGContextAddLineToPoint(context, lastPointX , lastPointY);

    CGContextStrokePath(context);

}

- (void)drawRect:(CGRect)rect {
    if (self.cgLayer == NULL) {
        CGLayerRef layer = CGLayerCreateWithContext(UIGraphicsContextGetCurrent(), self.bounds, NULL);
        self.cgLayer = layer;
        CGLayerRelease(layer);
    }

    ... various Core Graphics calls with self.cgLayer as the context ...

    CGContextDrawLayerInRect(UIGraphicsContextGetCurrent(), self.bounds, self.cgLayer);
}

- (void)setCgLayer:(CGLayerRef)aLayer {
    CGLayerRetain(aLayer);
    CGLayerRelease(cgLayer_);
    cgLayer_ = aLayer;
}