iOS 下載按鈕：DownloadButton

DownloadButton 是可自定義的 App Store 風格的下載按鈕。可自定義設計組件，用 IB 進行編輯。
使用示例：

#pragma mark - PKDownloadButtonDelegate


(void)downloadButtonTapped:(PKDownloadButton *)downloadButton 
          currentState:(PKDownloadButtonState)state {

  switch (state) {
  case kPKDownloadButtonState_StartDownload:
      self.downloadButton.state = kPKDownloadButtonState_Pending;
      [self.pendingSimulator startDownload];
  break;
  case kPKDownloadButtonState_Pending:
      [self.pendingSimulator cancelDownload];
      self.downloadButton.state = kPKDownloadButtonState_StartDownload;
  break;
      case kPKDownloadButtonState_Downloading:
      [self.downloaderSimulator cancelDownload];
      self.downloadButton.state = kPKDownloadButtonState_StartDownload;
  break;
  case kPKDownloadButtonState_Downloaded:
      self.downloadButton.state = kPKDownloadButtonState_StartDownload;
      self.imageView.hidden = YES;
  break;
  default:
      NSAssert(NO, @"unsupported state");
  break;

  }
}
#pragma mark - DownloaderSimulatorDelegate
(void)simulator:(PKDownloaderSimulator *)simulator didUpdateProgress:(double)progress {
  if (simulator == self.pendingSimulator) {
  if (progress == 1.) {
      self.downloadButton.state = kPKDownloadButtonState_Downloading;
      [self.downloaderSimulator startDownload];
  }

  }
  else if (simulator == self.downloaderSimulator) {
  self.downloadButton.stopDownloadButton.progress = progress;
  if (progress == 1) {
      self.downloadButton.state = kPKDownloadButtonState_Downloaded;
      self.imageView.hidden = NO;
  }

  }
}</pre>
 
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