在后台任务中将 cattextlayers 添加到 calayer

Question

我有一个情况，我不明白。我喜欢在后台任务中创建 CATextLayers 并在我的视图中显示它们，因为这需要一些时间。

无需后台任务即可完美运行。我可以立即在我的视图中看到文本 "worldmapview"

@IBOutlet var worldmapview: Worldmapview! // This view is just an empty view.

    override func viewDidLoad(){

         view.addSubview(worldmapview);

    }
func addlayerandrefresh_direct(){
                var calayer=CALayer();
                var newtextlayer:CATextLayer=create_text_layer(0,y1: 0,width:1000,heigth:1000,text:"My Text ....",fontsize:5);

                    self.worldmapview.layer.addSublayer(newtextlayer)
                    //calayer.addSublayer(newtextlayer);
                    calayer.addSublayer(newtextlayer)
                    self.worldmapview.layer.addSublayer(calayer);
                    self.worldmapview.setNeedsDisplay();
  }

在后台任务中执行此操作时，文本不会出现在我的视图中。有时，并非总是，它会在几秒钟后出现（例如 10）。

func addlayerandrefresh_background(){
            let qualityOfServiceClass = QOS_CLASS_BACKGROUND
            let backgroundQueue = dispatch_get_global_queue(qualityOfServiceClass, 0)

           dispatch_async(backgroundQueue, {

                var calayer=CALayer();
                var newtextlayer:CATextLayer=create_text_layer(0,y1: 0,width:1000,heigth:1000,text:"My Text ....",fontsize:5);
                dispatch_async(dispatch_get_main_queue(),{

                    self.worldmapview.layer.addSublayer(newtextlayer)
                    //calayer.addSublayer(newtextlayer);
                    calayer.addSublayer(newtextlayer)
                    self.worldmapview.layer.addSublayer(calayer);
                    self.worldmapview.setNeedsDisplay();
                })

            })
     }
    func create_text_layer(x1:CGFloat,y1:CGFloat,width:CGFloat,heigth:CGFloat,text:String,fontsize:CGFloat)  -> CATextLayer {
        let textLayer = CATextLayer()
        textLayer.frame = CGRectMake(x1, y1, width, heigth);
        textLayer.string = text
        let fontName: CFStringRef = "ArialMT"
        textLayer.font = CTFontCreateWithName(fontName, fontsize, nil)
        textLayer.fontSize=fontsize;
        textLayer.foregroundColor = UIColor.darkGrayColor().CGColor
        textLayer.wrapped = true
        textLayer.alignmentMode = kCAAlignmentLeft
        textLayer.contentsScale = UIScreen.mainScreen().scale
        return textLayer;
    }

有人看到了吗，怎么了？非常令人困惑的是：在后台对 CAShapeLayer 进行同样的操作。

Answer 1

UI 上的所有更改都在主线程上执行。您不能在后台线程上更新用户界面。根据Apple's documentation

Work involving views, Core Animation, and many other UIKit classes usually must occur on the app’s main thread. There are some exceptions to this rule—for example, image-based manipulations can often occur on background threads—but when in doubt, assume that work needs to happen on the main thread.

Answer 2

看起来 setNeedDisplay 不会导致子层重绘，我们需要在我们需要的所有层上调用它，在这种情况下它是新添加的层

func addlayerandrefresh_background(){
    let calayer = CALayer()
    calayer.frame = self.worldmapview.bounds

    dispatch_async(backgroundQueue, {
        for var i = 0; i < 100 ; i+=10 {
            let newtextlayer:CATextLayer=self.create_text_layer(0, y1: CGFloat(i) ,width:200,heigth:200,text:"My Text ....",fontsize:5)
            calayer.addSublayer(newtextlayer)
        }
        dispatch_async(dispatch_get_main_queue(),{
            self.worldmapview.layer.addSublayer(calayer)
            for l in calayer.sublayers! {
                l.setNeedsDisplay()
            }
        })

    })
}

在后台任务中将 cattextlayers 添加到 calayer

adding catextlayers to calayer in a background task

ios

swift

calayer

cashapelayer