停止绘制CATiledLayer

Question

是否可以停止CATiledLayer来绘制(drawLayer:inContext)？它是异步绘制的，当我尝试释放CATiledLayer使用的CGPDFDocumentRef时，应用程序崩溃(EXC_BAD_ACCESS)。

这就是我的观点：

@implementation TiledPDFView

- (id)initWithFrame:(CGRect)frame andScale:(CGFloat)scale{
    if ((self = [super initWithFrame:frame])) {

        CATiledLayer *tiledLayer = (CATiledLayer *)[self layer];
        tiledLayer.levelsOfDetail = 4;
        tiledLayer.levelsOfDetailBias = 4;
        tiledLayer.tileSize = CGSizeMake(512.0, 512.0);
        myScale = scale;
    }
    return self;
}

// Set the layer's class to be CATiledLayer.
+ (Class)layerClass {
    return [CATiledLayer class];
}

- (void)stopDrawing{
    CATiledLayer *tiledLayer = (CATiledLayer *)[self layer];
    [tiledLayer removeFromSuperlayer];
    tiledLayer.delegate = nil;
}
// Set the CGPDFPageRef for the view.
- (void)setPage:(CGPDFPageRef)newPage
{
    CGPDFPageRelease(self->pdfPage);
    self->pdfPage = CGPDFPageRetain(newPage);

    //self->pdfPage = newPage;
}


-(void)drawRect:(CGRect)r
{
}


// Draw the CGPDFPageRef into the layer at the correct scale.
-(void)drawLayer:(CALayer*)layer inContext:(CGContextRef)context
{   

    // First fill the background with white.
    CGContextSetRGBFillColor(context, 1.0,1.0,1.0,1.0);
    CGContextFillRect(context,self.bounds);

    CGContextSaveGState(context);
    // Flip the context so that the PDF page is rendered
    // right side up.
    CGContextTranslateCTM(context, 0.0, self.bounds.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);

    // Scale the context so that the PDF page is rendered 
    // at the correct size for the zoom level.
    CGContextScaleCTM(context, myScale,myScale);    
    CGContextDrawPDFPage(context, pdfPage);
    CGContextRestoreGState(context);

}

// Clean up.
- (void)dealloc {
    CGPDFPageRelease(pdfPage);

    [super dealloc];
}

这就是我尝试在视图控制器中停止并发布PDF的地方：v是TiledPDFView的实例

 -(void) stopDwaring {
     [v stopDrawing];
     [v removeFromSuperview];
     [v release];
     [self.view removeFromSuperview];
     self.view = nil;
     CGPDFDocumentRelease(pdf);

 }

Answer 1

这篇文章帮助我解决了我自己的CATiledLayer问题。我使用了Apple文档中的TiledPDFview.m作为示例。因为我需要在某个时刻重画整个视图和所有的瓦片，所以我使用CATiledLayer作为属性。当退出和释放视图控制器时，它崩溃了，并将CATiledLayer retain:消息发送到已释放的实例。下面是我的视图控制器的dealloc方法：

- (void)dealloc {
    self.tiledLayer.contents=nil;
    self.tiledLayer.delegate=nil;
    [self.tiledLayer removeFromSuperlayer];

    // note: releasing the layer still crashes- 
    // I guess removeFromSuperlayer releases it already, 
    // but couldn't find documentation so far.
    // So that's why it's commented out:
    // [self.tiledLayer release], self.tiledLayer=nil;

    //release the other viewcontroller stuff... 
    [super dealloc];
}

这对我很有效。希望这能帮助到别人。

Answer 2

在释放CGPDFDocumentRef之前，将CATiledLayer从其上层移除。

[yourTiledLayer removeFromSuperlayer];

别忘了把它的委派也设为零。

yourTiledLayer.delegate = nil;

在此之后，您可以安全地释放您的CGPDFDocumentRef。

添加代码后编辑：

你用CGPDFDocumentGetPage()得到pdfPage了吗？如果是这样，你就不应该释放它，它是一个自动释放的对象。

关于如何将其添加为子层:您实际上不需要TiledPDFView。在视图控制器中，您可以简单地执行以下操作：

CATiledLayer *tiledLayer = [CATiledLayer layer];
tiledLayer.delegate = self; //sets where tiledLayer will look for drawLayer:inContext:
tiledLayer.tileSize = CGSizeMake(512.0f, 512.0f);
tiledLayer.levelsOfDetail = 4;
tiledLayer.levelsOfDetailBias = 4;
tiledLayer.frame = CGRectIntegral(CGRectMake(0.0f, 0.0f, 512.0f, 512.0f));
[self.view.layer addSublayer:tiledLayer];

然后将您的drawLayer:inContext:实现移动到您的视图控制器。

然后在视图控制器的dealloc中，将其释放为：

[tiledLayer removeFromSuperlayer];
tiledLayer.delegate = nil;
CGPDFDocumentRelease(pdf);

请注意，您不能在UIView子类上执行此操作，因为UIView:inContext:将与UIView的主层冲突。

Answer 3

object.layer.contents =零

这应该等待线程完成。这对我的情况很有帮助。