title: AVCaptureMetadataOutput setMetadataObjectTypes unsupported type found
body: <p>I know there are someone have ask this question.But it is a sorry i donot find the answer.</p>
  
  <pre><code>dispatchQueue = dispatch_queue_create("myQueue", NULL);
  [captureMetadaOutput setMetadataObjectsDelegate:self queue:dispatchQueue];
  //  [captureMetadaOutput setMetadataObjectTypes:[NSArray arrayWithObject:AVMetadataObjectTypeQRCode]];
  //  设置条码类型
  captureMetadaOutput.metadataObjectTypes = @[AVMetadataObjectTypeQRCode];
  </code></pre>
  
  <p>i got crashes info from Crashlytics:</p>
  
  <blockquote>
    <p>[AVCaptureMetadataOutput setMetadataObjectTypes:] - unsupported type
    found.  Use -availableMetadataObjectTypes.</p>
  </blockquote>