没有调用Zbar委托方法

Question

继承启动UIImagePickerController的方法：

- (IBAction)startScan:(id)sender {

    ZBarReaderViewController *reader = [ZBarReaderViewController new];

    reader.readerDelegate = self;

    reader.readerView.torchMode = 1;

    ZBarImageScanner *scanner  = reader.scanner;

    [scanner setSymbology:ZBAR_I25 config:ZBAR_CFG_ENABLE to:0];

    [self presentModalViewController:reader animated:YES];

    reader = nil;

    resultTextView.hidden = NO;
}

但是在选择图像时，不会调用委托方法 - imagePickerController：didFinishPickingMediaWithInfo：。有谁能说出原因？