在backgroundtask中添加到CALayer时，不会显示UIImage [英] UIImage not displayed when added to CALayer in a backgroundtask

问题描述

在我的viewcontroller中我有：

in my viewcontroller I have:

@IBOutlet var worldmapview: Worldmapview!


var eventLayer:CALayer=CALayer();

和一些功能：

func create_picture_layer(pathtopic:String) -> CALayer {
    let bm=getImage(pathtopic,fBitmapsizeSelected: 100)!;
    var calayer_for_picture=CALayer();
    calayer_for_picture.frame=CGRectMake(100, 100, 100, 100);
    calayer_for_picture.contents = bm.CGImage;
    return calayer_for_picture;
}

func createCircleShape(x:CGFloat,y:CGFloat, size:CGFloat) -> CAShapeLayer {

    var test2:UIBezierPath=UIBezierPath(ovalInRect: CGRectMake(x - size/2, y - size/2, size, size));

    var shapelayer:CAShapeLayer=CAShapeLayer();
    shapelayer.backgroundColor=UIColor.clearColor().CGColor;
    //shapelayer.frame=CGRectMake(0, 0, 300, 300);
    shapelayer.fillColor=UIColor.darkGrayColor().CGColor;
    shapelayer.path=test2.CGPath;
    shapelayer.opaque=true

    return shapelayer;
}

func getImage(simagename: String, fBitmapsizeSelected:CGFloat) -> UIImage?{

    var sPathToImage:String=AppProperties.sharedInstance.sPicturePath + simagename;
    let checkValidation = NSFileManager.defaultManager()

    if (!checkValidation.fileExistsAtPath(sPathToImage) || simagename.equals("")){
        // Path to unknown image
        let sunknownimagename:String = "na/na.jpa";
        sPathToImage=AppProperties.sharedInstance.sPicturePath + sunknownimagename;
    }

    let bm:UIImage=UIImage(contentsOfFile: sPathToImage)!;
    var bMapScaled:UIImage;
    if(!bm.isEqual(nil)){
        let newSize:CGSize=CGSizeMake(fBitmapsizeSelected, fBitmapsizeSelected);
        bMapScaled = bm.imageByScalingToSize(newSize,contentMode: UIViewContentMode.ScaleAspectFill)!;
        return bMapScaled;
    }else{
        return nil;
    }
}

在我的 viewDidAppear（动画） ：Bool）方法我尝试在worldmapview中显示图像

In my viewDidAppear(animated: Bool) method I try to show the image in worldmapview

以下代码在没有任何后台任务的情况下正常工作。图像立即显示。

the following code works fine without any background tasks. The image is shown immediately.

// works
let thepicturelayer=create_picture_layer("mypicpath")
eventLayer.addSublayer(thepicturelayer);
worldmapview.layer.addSublayer(eventLayer);
eventLayer.setNeedsDisplay();

并且在主任务中刷新它对我不起作用。图片未显示。一段时间后它会出现，但并非总是如此。

in a background task and refreshing in the main task it doesn't work for me. Picture is not shown. After a while it appears, but not always.

// doesn't work

        let qualityOfServiceClass = QOS_CLASS_BACKGROUND
        let backgroundQueue = dispatch_get_global_queue(qualityOfServiceClass, 0)

        dispatch_async(backgroundQueue, {
            // geht auch mit Eventlayer

            let thepicturelayer=self.create_picture_layer() // This Shape doesn't appear.
            let circleshapelayer=self.createCircleShape(200, y: 200, size: 20) // This shape appears immediatelly.

            self.eventLayer.addSublayer(thepicturelayer);
            self.eventLayer.addSublayer(circleshapelayer);


            dispatch_async(dispatch_get_main_queue(),{
                    //assert(self.eventLayer.sublayers?.count > 0,"no layers in eventLayer !") // just added

                    self.worldmapview.layer.addSublayer(self.eventLayer);
                    //assert(self.worldmapview.layer.sublayers!.count > 0,"no layers in worldmapview!" ) // just added
                    let sublayers=self.eventLayer.sublayers;
                    if sublayers != nil {
                        for l in self.eventLayer.sublayers! {
                            l.setNeedsDisplay()
                        }
                    }
                    //self.updateWorldMapGUI();
                    self.worldmapview.layer.addSublayer(self.eventLayer);
                    //thepicturelayer.setNeedsDisplay();
                    //circleshapelayer.setNeedsDisplay();
                    self.eventLayer.setNeedsDisplay();

            })
        })

更新

我使用新的CAShapelayer以相同的方式更新了代码，该方法立即显示。我不明白其中的区别。在后台任务中创建时，图片不会显示。

I updated the code with a new CAShapelayer added the same way, which is displaying immediately. I do not understand the difference. The Picture is not shown, when created in a background task.

UPDATE2

我意识到一些让我感到困惑的事情：
以下代码没有后台任务，如前所述：

I realized something confusing to me additionally: Following Code without background task works as already described:

    let thepicturelayer=create_picture_layer()
    eventLayer.addSublayer(thepicturelayer);
    worldmapview.layer.addSublayer(eventLayer);
    eventLayer.setNeedsDisplay();
    //thepicturelayer.setNeedsDisplay(); // When adding this, the picture is not shown.

但是激活最后一行，图片不会出现。可能它与它有关？似乎calayer的内容已经消失了？

But activating the last line, the picture doesn't appear. Probably it has something to do with it ? It seems like the content of the calayer is gone ?

推荐答案

据我所知，你正在创建 CALayer 在后台，和也将该图层添加到后台的UI层次结构中。

As I understand it, you are creating CALayer in the background, and adding that layer to the UI hierarchy in the background as well.

它会不会是否合理地认为所有UI修改都发生在 main 线程中？如果是这样，试试这个：

Would it be reasonable to think that all UI modifications are to happen in the main thread? If so, try this:

let qualityOfServiceClass = QOS_CLASS_BACKGROUND
let backgroundQueue = dispatch_get_global_queue(qualityOfServiceClass, 0)

dispatch_async(backgroundQueue, {
    let thepicturelayer=self.create_picture_layer()

    dispatch_async(dispatch_get_main_queue(),{
        self.eventLayer.addSublayer(thepicturelayer);
        assert(self.eventLayer.sublayers) // just added

        self.worldmapview.layer.addSublayer(self.eventLayer);
        assert(self.worldmapview.layer.sublayers) // just added

        self.worldmapview.setNeedsDisplay()
    })
})

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