摘要：
我无法强制 CALayer 正确响应方向变化。每当我尝试使用 cgaffinetransform 时，我都会得到奇怪的结果（图层未居中）。任何帮助将不胜感激！谢谢，
过程 我正在使用 AVCaptureVideoPreviewLayer 子类添加视频预览。当设备处于纵向时，一切看起来都很好。当设备旋转到横向（左或右）或纵向倒置时会出现问题。
我正在使用 AVCaptureVideoPreviewLayer 子类添加视频预览。当设备处于纵向时，一切看起来都很好。当设备旋转到横向（左或右）或纵向倒置时会出现问题。
我正在使用以下代码添加预览层：
CGRect layerRect = [[[self view] layer] bounds];
[[[self captureManager] previewLayer] setBounds:layerRect];
[[[self captureManager] previewLayer]setFrame:CGRectMake(0, height, width, height)];
[[[self captureManager] previewLayer] setPosition:CGPointMake(CGRectGetMidX(layerRect),CGRectGetMidY(layerRect))];
并且在纵向模式下正确显示。当我尝试旋转设备时，预览层的行为很奇怪。它似乎没有自行调整大小，也没有正确旋转。
我尝试通过添加以下方法来修复它
-(void)rotateLayer{
CALayer * stuckview = [[self captureManager] previewLayer];
CGRect layerRect = [[[self view] layer] bounds];
UIDeviceOrientation orientation =[[UIDevice currentDevice]orientation];
switch (orientation) {
case UIDeviceOrientationLandscapeLeft:
stuckview.affineTransform = CGAffineTransformMakeRotation(M_PI+ M_PI_2); // 270 degress
NSLog(@"Landscape Left");
[stuckview setPosition: CGPointMake(self.view.bounds.size.width /2.0, self.view.bounds.size.height /2.0)];
break;
case UIDeviceOrientationLandscapeRight:
stuckview.affineTransform = CGAffineTransformMakeRotation(M_PI_2); // 90 degrees
NSLog(@"Landscape Right");
[stuckview setPosition: CGPointMake(self.view.bounds.size.width /2.0, self.view.bounds.size.height /2.0)];
break;
case UIDeviceOrientationPortraitUpsideDown:
stuckview.affineTransform = CGAffineTransformMakeRotation(M_PI); // 180 degrees
NSLog(@"Landscape Upside down");
break;
default:
stuckview.affineTransform = CGAffineTransformMakeRotation(0.0);
break;
}
float h1 = stuckview.frame.size.height;
float w1 = stuckview.frame.size.width;
if(UIDeviceOrientationIsPortrait(orientation))
{
stuckview.position =CGPointMake(h1/2.0, w1/2.0);
NSLog(@"Portrait");
}
else{
stuckview.position =CGPointMake(w1/2.0, h1/2.0);
NSLog(@"Portrait");
}
}
添加上面的方法后，我可以看到一个进度。现在图层可以正确旋转以反映当前设备方向，并且可以在横向模式下正确显示，但不能在纵向模式下显示。
图层定位不正确，不在屏幕中心（看截图）。要查看发生了什么，我添加了以下调试语句：
CALayer * stuckview = [[self captureManager] previewLayer];
CGRect layerRect = [[[self view] layer] bounds];
float h = stuckview.bounds.size.height;
float w = stuckview.bounds.size.width;
float x = stuckview.bounds.origin.x;
float y = stuckview.bounds.origin.y;
float h1 = stuckview.frame.size.height;
float w1 = stuckview.frame.size.width;
float x1 = stuckview.frame.origin.x;
float y1 = stuckview.frame.origin.y;
NSLog(@"%f %f %f %f ", h,w,x,y );
NSLog(@"%f %f %f %f ", h1,w1,x1,y1 );
NSLog(@"Anchor Point: %f %f",stuckview.anchorPoint.x, stuckview.anchorPoint.y);
NSLog(@"Position: %f %f",stuckview.position.x, stuckview.position.y);
CGAffineTransform at = stuckview.affineTransform;
NSLog(@"Affine Transform After : %f %f %f %f %f %f %f", at.a,at.b, at.c, at.d, at.tx,at.tx, at.ty);
并得到以下输出：
2012-09-30 13:25:12.067 RotatePreviewLayer[2776:907] 1024.000000 768.000000 0.000000 0.000000
2012-09-30 RotatePreviewLayer[2776:907] 1024.000000 768.000000 128.000000 -128.000000
2012-09-30 13:25:12.070 RotatePreviewLayer[2776:907] Portrait
2012-09-30 13:25:12.072 RotatePreviewLayer[2776:907] Anchor Point: 0.500000 0.500000
2012-09-30 13:25:12.074 RotatePreviewLayer[2776:907] Position: 512.000000 384.000000
2012-09-30 13:25:12.076 RotatePreviewLayer[2776:907] Affine Transform after: -1.000000 0.000000 -0.000000 -1.000000 0.000000 0.000000 0.000000
注意调试输出的第二行。预览层的框架移动了128，-128。谁能解释一下为什么会发生这种情况以及如何解决预览层的方向问题？谢谢你，亚努斯