问题描述
我正在做GPS跟踪应用。每次收到纬度/经度时,它会将其转换为(x,y)坐标,并调用 drawRect
在两个(x,y)对之间绘制一条线。
I'm doing a GPS tracking app. Every time it receives a Latitude/Longitude it converts it to (x,y) coordinates and calls drawRect
to draw a line between two (x,y) pairs.
然而,drawRect方法只是在绘制新东西之前清除所有旧内容。如何让drawRect在现有画布上绘制新东西?提前致谢
However, the drawRect method just clear all the old contents before it draw new thing. How I can make the drawRect to draw new thing on the existing canvas? Thanks in advance
这是我的viewController.h
here is my viewController.h
#import <UIKit/UIKit.h>
#import <CoreLocation/CoreLocation.h>
@class routetrack;
@interface simpleDrawViewController : UIViewController <CLLocationManagerDelegate> {
CLLocationManager *locationManager;
IBOutlet routetrack *routeroute;
float latOld;
float longOld;
float latNew;
float longNew;
}
- (IBAction) gpsValueChanged;
@property (nonatomic,retain) CLLocationManager *locationManager;
@property (retain,nonatomic) routetrack *routeroute;
ViewController.m
ViewController.m
#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
我的绘图类,UIView的子类
my drawing class, a subclass of UIView
#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);
}
推荐答案
UIView确实没有画布模型。如果你想保留画布,你应该创建一个 CGLayer
或一个 CGBitmapContext
并绘制到它上面。然后在你的视图中绘制。
UIView does not have a canvas model. If you want to keep a canvas, you should create a CGLayer
or a CGBitmapContext
and draw onto that. Then draw that in your view.
我会为 CGLayerRef
创建一个ivar,然后 drawRect:
看起来像这样(未经测试):
I would create an ivar for a CGLayerRef
, and then drawRect:
would look something like this (untested):
- (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);
}
每当你想要清除画布时,只需 self .cgLayer = NULL
。
Whenever you wanted to clear your canvas, just self.cgLayer = NULL
.
setCgLayer:
将是这样的:
- (void)setCgLayer:(CGLayerRef)aLayer {
CGLayerRetain(aLayer);
CGLayerRelease(cgLayer_);
cgLayer_ = aLayer;
}
这篇关于如何使用drawRect在现有视图中绘制?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!