从C函数更新进度条

Question

从C函数更新进度条

cswiftpointersgrand-central-dispatchcore-audio

3

我正在使用Swift为iOS 8开发一款音频应用程序。该应用程序可以加载MIDI文件，当用户单击“保存”按钮时，它会渲染到文件中。在C函数中，需要手动提取样本。
现在，我想要更新界面上的进度条以反映保存进度。
我在ViewController中添加了一个属性观察器来监测变量，我将这个变量的指针传递给C函数，希望能够在循环过程中更新值。然而，即使C函数在循环内部更新了变量的值，这个更新只会在最后被“触发”。
有没有办法更新进度条？
下面是一些代码。
谢谢！

在ViewController中:

var outProgressBarValue:Float = 0.0 {
    willSet {
        dispatch_async(dispatch_get_main_queue(), {
            println("New value received! -> \(newValue)")
            self.progressBarOutlet.setProgress(newValue, animated: true)
        })
    }
}

@IBAction func saveButton(sender: AnyObject) {
    [...]
    let backgroundQueue = dispatch_get_global_queue(QOS_CLASS_DEFAULT, 0)
    dispatch_async(backgroundQueue, {
        WriteOutputFile(url, self.musicSequence!, Sound.sharedInstance.musicPlayer, self.processingGraph,  &self.outProgressBarValue)

    dispatch_async(dispatch_get_main_queue(), {
            restoreOnlineRendering(processingGraph: self.processingGraph, mainMixerNode: self.mainMixerNode, ioNode: &(self.ioNode))
            self.saveButtonOutlet.setTitle("Done", forState: UIControlState.Normal)
    [...]
}

在一个链接的C文件中：

void WriteOutputFile(CFURLRef url, MusicSequence musicSequence, MusicPlayer musicPlayer, AUGraph processingGraph, float *outProgressBarValue) {  
[…] 
    CheckError(MusicPlayerStart(musicPlayer), "MusicPlayerStart");
    do {
        CheckError(AudioUnitRender (outputUnit, &actionFlags, &tStamp, 0, numFrames, bufferList), "AudioUnitRender");
        tStamp.mSampleTime += (Float64)numFrames;
        CheckError(ExtAudioFileWrite(outfile, numFrames, bufferList), "ExtAudioFileWrite");
        CheckError(MusicPlayerGetTime (musicPlayer, &currentTime), "MusicPlayerGetTime");
        *outProgressBarValue = currentTime / sequenceLength;
        printf("outProgressBarValue:\t %f\n", *outProgressBarValue);
    } while (currentTime < sequenceLength);

    CheckError(MusicPlayerStop(musicPlayer), "MusicPlayerStop"); 
[…] 
}

- popisar

1个回答

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- Mundi · Accepted Answer

如果观察无效，为什么不通过NSNotification将更新显式发送到控制器呢？以下是我作为概念验证所做的事情：

Add an Objective-C class file with .h and .m files. No need to define a class in this file, just put your c function in .m, and the declaration in .h.
Configure the bridging header, where you import the .h file. The bridging header is typically called "-Bridging-Header.h".
You can now just call your function in any swift class.
In the .m file with the c function, import "<UIKit/UIkit.h>" (or Foundation).

When needed, post a notification from your c function similar to this:

NSNotification *notif = [[NSNotification alloc] initWithName:@"Update"
   object:nil userInfo:@{@"progress" : @0.42}];
[[NSNotificationCenter defaultCenter] postNotification:notif];

In the swift file, follow the usual procedure to add self as observer for the notification and call the update function with the values passed in the userInfo dictionary.