如何在iPhone手势中绘制图形？
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我有一个问题要在用户在iPhone上进行平移手势（即用户触摸并拖动手指）后绘制线条或圆圈指示器。但是，UIGraphicsGetCurrentContext（）始终返回nil，有人知道如何在iPhone上实现吗？
谢谢，
lu
@interface MyView : UIView <UIGestureRecognizerDelegate> {
CGPoint location;
PanIndicator *panIndicator;
}
@implementation MyView
- (id)init {
if (self = [super init]) {
UIPanGestureRecognizer *panGesture = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(panAction:)];
[panGesture setMaximumNumberOfTouches:1];
[panGesture setDelegate:self];
[self addGestureRecognizer:panGesture];
[panGesture release];
panIndicator = [[PanIndicator alloc] init];
[self addSubview:panIndicator];
}
return self;
}
- (void)panAction:(UIPanGestureRecognizer *)gR {
if ([gR state]==UIGestureRecognizerStateBegan) {
location = [gR locationInView:self];
} else if ([gR state]==UIGestureRecognizerStateEnded) {
// The following code in this block is useless due to context = nil
// CGContextRef context = UIGraphicsGetCurrentContext();
// CGContextAddRect(context, CGRectMake(30.0, 30.0, 60.0, 60.0));
// CGContextStrokePath(context);
} else if ([gR state]==UIGestureRecognizerStateChanged) {
CGPoint location2 = [gR locationInView:self];
panIndicator.frame = self.bounds;
panIndicator.startPoint = location;
panIndicator.endPoint = location2;
// [panIndicator setNeedsDisplay]; //I don\'t know why PanIncicator:drawRect doesn\'t get called
[panIndicator drawRect:CGRectMake(0, 0, 100, 100)]; //CGRectMake is useless
}
}
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2 个回复
僻朵庙惩竣
中调用，并在myCanvasView方法中绘制此轨道。 像这样：- (void)panAction:(UIPanGestureRecognizer *)gR { [myData addPoint:[gR locationInView:gR.view]]; [myCanvasView setNeedsDisplay]; } - (void)drawInRect:(CGRect)rect { [self drawLinesFromData:myData]; }@interface PanIndicator : UIView {} @property (nonatomic, assign) CGPoint startPoint; @property (nonatomic, assign) CGPoint endPoint; @end @implementation PanIndicator @synthesize startPoint = startPoint_; @synthesize endPoint = endPoint_; - (void)drawRect:(CGRect)aRect { [[UIColor redColor] setStroke]; UIBezierPath *pathToDraw = [UIBezierPath bezierPath]; [pathToDraw moveToPoint:self.startPoint]; [pathToDraw addLineToPoint:self.endPoint]; [pathToDraw stroke] } @end熊融炭臀陛
开始绘制。 实现的问题在于，您无需从手势的跟踪方法中设置图形上下文。当视图标记为需要重绘时（通过\'setNeedsDisplay \'），可以为您完成此操作。 这样做的原因是可以将视图的内容缓存在一个图层中，这对于优化动画和合成非常重要。因此，如果需要绘制视图，请调用并通过方法进行绘制，以使界面的其余部分与更改保持同步。