从解析查询块返回 UIImage 数组 [英] Return UIImage Array From Parse Query Block

问题描述

我无法从该函数中获得 [UIImage?] 返回值.getDataInBackgroundWithBlock 不会让我设置除 Void in 以外的返回值.但是，该块会在迭代时添加到 iconArray 中.但是一旦在块之外，数组又是空的.您将在下面的代码中看到数组正确打印和未正确打印的注释.

I cannot get a [UIImage?] return from this function. The getDataInBackgroundWithBlock won't let me set a return value other than Void in. However, that block does add to the iconArray as it iterates through. But once outside of the block the array is empty again. You will see in the code below the comments where the array does and does not print correctly.

调用确实连接到数据库，所有数据都在流动.它只是返回那个挂断的数组.

The call does connect to the DB, all data is flowing. It's simply returning that array that is the hang up.

class callData {


func queryImages() -> [UIImage?] {

    var iconArray: [UIImage?] = []

    var query: PFQuery = PFQuery(className: "QuestionMaster")
    query.findObjectsInBackgroundWithBlock { (objects: [AnyObject]?, error: NSError?) -> Void in

        for object in objects! {

            let imageFiles = object["questionImage"] as! PFFile

            imageFiles.getDataInBackgroundWithBlock({
                (imageData: NSData?, error: NSError?) -> Void in
                if (error == nil) {

                    let image = [UIImage(data: imageData!)]
                    iconArray += image        //adds item to array correctly
                }

                println(iconArray) //prints correct array here

            }) //getDataInBackgroundWithBlock close

            println(iconArray) //does not print correct array here

        } //for-loop close

    }

    return iconArray //returns empty array

}

}

推荐答案

当您的函数声明该块在后台执行时(在异步线程上.这意味着它将在后台加载，但也会继续执行函数的其余部分，从而返回一个空数组.

As your function states the block is executed in the background (on a asynchronous thread. This means that it will load in the background but will also continue the rest of the function thus returning an empty array.

要解决此问题，您应该在后台为块使用完成处理程序.

To fix this you should use a completion handler for your block in background.

func queryImages(onComplete:(images: [UIImage?])-> Void){
    var iconArray: [UIImage?] = []
    var query: PFQuery = PFQuery(className: "QuestionMaster")
    query.findObjectsInBackgroundWithBlock { (objects: [AnyObject]?, error: NSError?) -> Void in

    for object in objects! {

        let imageFiles = object["questionImage"] as! PFFile

        let imageData = imageFiles.getData()
        let image = UIImage(data:imageData!)
        iconArray.append(image)

        println(iconArray)
    }
    onComplete(images: iconArray)
    }
}

虽然上面的代码未经测试应该可以工作

Although untested above code should work

for 循环中的异步数据检索已被替换为同步调用以简化项目

The Asynchronous data retrieval inside your for loop has been replaced in favor of a synchronous call to ease the project

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