如何使用UIPanGestureRecognizer在iOS中拖線

Question

我正在編寫一個程序，用戶將一條線從一個UILabel拖到另一個。 我創建了一個名為DragView的UIView子類，並覆蓋了drawRect方法。 我將UIView RootController視圖的子視圖。 DragView是絕對可見的， drawRect方法是絕對被調用的，但是沒有一行可見。

這些是（我認為是）相關的代碼段。

//DragView.m

- (void)drawRect:(CGRect)rect
{
    if (context == nil)
    {
        context = UIGraphicsGetCurrentContext();
    }

    if (_drawLineFlag)
    {

        CGContextSetLineWidth(context,2.0); 
        CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
        CGFloat components[] = {0.0,0.0,1.0,1.0};
        CGColorRef color = CGColorCreate(colorspace, components);

        CGContextSetStrokeColorWithColor(context,color);

        CGContextMoveToPoint(context,_startX, _startY);

        CGContextAddLineToPoint(context,_currentX,_currentY);

        CGContextStrokePath(context);   
    } 
}    

DrawProgramAppDelegate

- (void) initializeUI
{
.....

    dragView = [[DragView alloc] initWithFrame:CGRectMake(0.0f,0.0f,1024.0f,768.0f)] ;
    [view addSubview: dragView];
    UIPanGestureRecognizer *panGestureRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self  action:@selector(handlePan:)];
    [dragView addGestureRecognizer:panGestureRecognizer];
.....

}

事件處理程序為：

- (void) handlePan:(UIPanGestureRecognizer *) recognizer             
{
    CGPoint point = [recognizer translationInView:dragView];

    [dragView setCurrentX:point.x];
    [dragView setCurrentY:point.y];
    [dragView setDrawLineFlag:YES];

    [view bringSubviewToFront:drawView];
    [dragView drawRect:CGRectMake (0.0f,0.0f,768.0f, 1024.0f)];
}

非常感謝您的幫助。

喬恩

Answer 1

在我看來，您正在嘗試畫一條路（您應該看一下這篇文章 ）。 在這里，您似乎只是從最后一點到當前點畫一條線

CGContextMoveToPoint(context,_startX, _startY);
CGContextAddLineToPoint(context,_currentX,_currentY);

給定通話頻率只會畫一條小線。

您不應該調用drawRect：

[dragView drawRect:CGRectMake (0.0f,0.0f,768.0f, 1024.0f)];

您應該告訴系統視圖需要顯示

[dragView setNeedsDisplay];

另外，您還應該檢查手勢識別器狀態，定義為

typedef enum {
   UIGestureRecognizerStatePossible,
   UIGestureRecognizerStateBegan,
   UIGestureRecognizerStateChanged,
   UIGestureRecognizerStateEnded,
   UIGestureRecognizerStateCancelled,
   UIGestureRecognizerStateFailed,
   UIGestureRecognizerStateRecognized = UIGestureRecognizerStateEnded
} UIGestureRecognizerState;

並且可能僅在狀態為UIGestureRecognizerStateChanged或UIGestureRecognizerStateEnded繪制