iPhone 4 中 IOS 7 中奇怪的 UIScrollview 行为答案

【问题标题】：Weird UIScrollview behaviour in IOS 7 in IPhone 4iPhone 4 中 IOS 7 中奇怪的 UIScrollview 行为
【发布时间】：2014-06-20 12:37:02
【问题描述】：

我正在开发一个与视频相关的应用程序。为此，我使用了AVFoundation 框架来捕获图像和视频。我正在捕获图像并在下一个视图中显示捕获的图像，其中图像视图是subview 到scrollview。它在 iPhone 5、iPhone 5s 和 iPad 中运行良好，但在 iPhone 4 中捕获图像并附加到 scrollView 后，应用程序变得缓慢。滚动视图不像在其他设备中那样平滑滚动。我没有遇到错误的问题。我正在使用以下代码来捕获图像：

-(void)capturePhoto
{
    _ciContext = [CIContext contextWithOptions:nil];
AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
//  - input
AVCaptureDeviceInput *deviceInput = [AVCaptureDeviceInput deviceInputWithDevice:device error:NULL];
NSError *error = nil;
if ([device lockForConfiguration:&error])
{
    if ([device isFlashModeSupported:AVCaptureFlashModeOff])
    {
        device.flashMode = AVCaptureFlashModeOff;
    }

    [device unlockForConfiguration];
}
//  - output
_dataOutput = [[AVCaptureStillImageOutput alloc] init];
NSDictionary *outputSettings = [[NSDictionary alloc] initWithObjectsAndKeys:
                                AVVideoCodecJPEG, AVVideoCodecKey, nil];
_dataOutput.outputSettings = outputSettings;
//  - output
NSMutableDictionary *settings;
settings = [NSMutableDictionary dictionary];
[settings setObject:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA]
             forKey:(__bridge id) kCVPixelBufferPixelFormatTypeKey];
_dataOutputVideo = [[AVCaptureVideoDataOutput alloc] init];
_dataOutputVideo.videoSettings = settings;
[_dataOutputVideo setSampleBufferDelegate:self queue:dispatch_get_main_queue()];
_session = [[AVCaptureSession alloc] init];
[_session addInput:deviceInput];
[_session addOutput:_dataOutput];
[_session addOutput:_dataOutputVideo];
  // _session.sessionPreset = AVCaptureSessionPresetPhoto;
  _session.sessionPreset = AVCaptureSessionPresetHigh;
   // _session.sessionPreset = AVCaptureSessionPresetMedium;
[_session startRunning];
// add gesture
//  UIGestureRecognizer *gr = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(didTapGesture:)];
// gr.delegate = self;
// [self.touchView addGestureRecognizer:gr];
_focusView = [[UIView alloc] init];
CGRect imageFrame = _focusView.frame;
imageFrame.size.width = 80;
imageFrame.size.height = 80;
_focusView.frame = imageFrame;
_focusView.center = CGPointMake(160, 202);
CALayer *layer = _focusView.layer;
layer.shadowOffset = CGSizeMake(2.5, 2.5);
layer.shadowColor = [[UIColor blackColor] CGColor];
layer.shadowOpacity = 0.5;
layer.borderWidth = 2;
layer.borderColor = [UIColor yellowColor].CGColor;
[self.touchView addSubview:_focusView];
_focusView.alpha = 0;
_isShowFlash = NO;
[self.view bringSubviewToFront:self.touchView];
UIView *footerView = [self.view viewWithTag:2];
[self.view bringSubviewToFront:footerView];
}

稍后我将像这样附加到滚动视图：

scrollImgView=[[UIImageView alloc]initWithFrame:CGRectMake(0, 0, 320, 340)];
        UIImage *image = [UIImage imageWithData:appdelegate.capturedImgData];
        UIImage *tempImage=[self resizeImage:image withWidth:320 withHeight:340];
        NSData *imgData=UIImageJPEGRepresentation(tempImage,1.0);//0.25f
        NSLog(@"image  is %@",image);
        scrollImgView.image=[UIImage imageWithData:imgData];
        // scrollImgView.contentMode = UIViewContentModeScaleAspectFit;
        // UIViewContentModeScaleAspectFit;
        [postScrollView addSubview:scrollImgView];

如果有人遇到同样的问题，请给我建议。

【问题讨论】：

标签： ios iphone ios7 uiscrollview avfoundation

【解决方案1】：

你的编码没问题，设备也没有问题，可能会发生

1. network problem

2. device memory is already loaded fully.

3. some Data conversation also taken times

这里

    UIImage *image = [UIImage imageWithData:appdelegate.capturedImgData];   
    UIImage *tempImage=[self resizeImage:image withWidth:320 withHeight:340];  //
    NSData *imgData=UIImageJPEGRepresentation(tempImage,1.0);//0.25f


 the above code u having used

 1. data conversion is taken high and also taken the 2 time of image conversion   optimize any `NSData`

 2. third line is improve the `quality` of your image-- this also take the time for image conversion.

在我的建议中

1. use `Asychronous method`

  -- sdwebimage  
  -- Asychronous Imageview
  -- NSOperation_Queue
  -- Dispatch im main_queue

使用其中的任何一个，它将为您获取一些响应。我的建议是使用SDWebImage.. 使用此链接Loading takes a while when i set UIImage to a NSData with a url.

【讨论】：

【解决方案2】：

我通过改变解决了这个问题

_session.sessionPreset = AVCaptureSessionPresetHigh到

_session.sessionPreset = AVCaptureSessionPresetMedium

【讨论】：