在三星手機上拍照失敗

Question

我正在使用Xamarin編寫Android應用程序，該應用程序具有用於使用Camera API捕獲圖片的自定義活動。這項活動完全適用於我測試過的所有設備，但是有些用戶在嘗試拍攝照片時報告應用程序崩潰。很明顯，所有這些用戶都使用三星手機，不幸的是我沒有一個可以測試。

謝天謝地，我已經能夠捕獲到異常和堆棧跟蹤，但是我很遺憾，可能會導致這個問題。下面是異常，堆棧跟蹤和有問題的代碼。

這是一個相當簡單的活動，全屏​​相機預覽，閃光切換和捕捉按鈕。它使用定製的CameraHelper類來設置和與Camera API進行交互。在用戶能夠進行交互並觸發TakePicture方法之前，配置攝像頭並通過OnSurfaceTextureAvailable方法顯示預覽。

異常堆棧跟蹤

java.lang.RuntimeException: takePicture failed 
android.hardware.Camera.native_takePicture(Native Method):0 
android.hardware.Camera.takePicture(Camera.java:1523):0 
android.hardware.Camera.takePicture(Camera.java:1468):0 
md5efa7d89b8a471e1a97a183b83296df21.CameraHelper.n_onAutoFocus(Native Method):0 
md5efa7d89b8a471e1a97a183b83296df21.CameraHelper.onAutoFocus(CameraHelper.java:39):0 

方法在CameraHelper

// Implements Camera.IPictureCallback and Camera.IAutoFocusCallback 

public void OnSurfaceTextureAvailable(object sender, TextureView.SurfaceTextureAvailableEventArgs e) 
{ 
    // Get the camera and set its orientation 
    try 
    { 
    _camera = Camera.Open(_cameraInt); 
    } 
    catch (Exception ex) 
    { 
    _callback.OnInitializationFailed(ex); 
    return; 
    } 

    var orientation = GetDisplayOrientation(); 
    _camera.SetDisplayOrientation(orientation); 

    // Set the camera parameters 
    var cameraParameters = _camera.GetParameters(); 

    if (cameraParameters.SupportedFocusModes != null && cameraParameters.SupportedFocusModes.Contains(Camera.Parameters.FocusModeContinuousPicture)) 
    cameraParameters.FocusMode = Camera.Parameters.FocusModeContinuousPicture; 

    if (cameraParameters.SupportedFlashModes != null && cameraParameters.SupportedFlashModes.Contains(Camera.Parameters.FlashModeAuto)) 
    { 
    cameraParameters.FlashMode = Camera.Parameters.FlashModeAuto; 
    HasFlash = true; 
    } 

    cameraParameters.JpegQuality = JPEG_QUALITY; 

    // Set the picture resolution 
    var pictureSize = GetIdealPictureSize(cameraParameters.SupportedPictureSizes, MAX_MEGAPIXELS); 
    _imageWidth = pictureSize.Width; 
    _imageHeight = pictureSize.Height; 
    cameraParameters.SetPictureSize(pictureSize.Width, pictureSize.Height); 

    // Set the preview resolution to best match the TextureView 
    var previewSize = GetIdealPreviewSize(cameraParameters.SupportedPreviewSizes, _previewTexture.Height, _previewTexture.Width); 
    cameraParameters.SetPreviewSize(previewSize.Width, previewSize.Height); 

    // Begin outputting camera preview 
    _camera.SetParameters(cameraParameters); 
    _camera.SetPreviewTexture(_previewTexture.SurfaceTexture); 
    _camera.StartPreview(); 
    UpdatePreviewTextureMatrix(); // Ensure the preview is displayed without warping 

    // Wait for the preview 
    EventHandler<TextureView.SurfaceTextureUpdatedEventArgs> h = null; 
    _previewTexture.SurfaceTextureUpdated += h = (s, e2) => 
    { 
    _previewTexture.SurfaceTextureUpdated -= h; 
    _callback.OnCameraPreviewReady(); 
    _ready = true; 
    }; 
} 

public void TakePicture() 
{ 
    if (!_ready || _busy) 
    { 
    var e = new Exception("Camera not ready"); 
    OnTakePictureFailed(e); 
    return; 
    } 

    _busy = true; 

    _camera.AutoFocus(this); 
} 

public void OnAutoFocus(bool success, Camera camera) 
{ 
    try 
    { 
    _camera.TakePicture(null, null, this); 
    } 
    catch (Exception e) 
    { 
    // On Samsung phones the exception is always thrown here 
    OnTakePictureFailed(e); 
    } 
} 

public void OnPictureTaken(byte[] data, Camera camera) 
{ 
    _busy = false; 
    var rotation = GetPictureRotation(); 
    _callback.OnPictureTaken(data, rotation, _imageWidth, _imageHeight); 
} 

private void OnTakePictureFailed(Exception e) 
{ 
    _busy = false; 
    _callback.OnTakePictureFailed(e); 
} 

相機可用並且預覽顯示沒有問題，異常只扔在三星設備。

Answer 1

當三星Galaxy手機第一次無法自動對焦時，會引發異常 - 而大多數設備只會嘗試對焦一次，Samsung Galaxy手機會重新嘗試三次，並且在每次嘗試後都會撥打OnAutoFocus回撥。因爲我的代碼在回調中調用了Camera.TakePicture，所以它可能會連續快速調用兩次或更多次，因此它會在圖片已經被拍攝時嘗試拍照並拋出異常。

的解決方式是增加其跟蹤自動對焦回調是否已經發生了一個布爾值，如果是這樣，跳過調用Camera.TakePicture：

public void OnAutoFocus(bool success, Camera camera) 
{ 
    if (_hasAttemptedFocus) return; 
    else _hasAttemptedFocus = true; 

    _camera.TakePicture(null, null, this); 
} 

public void OnPictureTaken(byte[] data, Camera camera) 
{ 
    _busy = _hasAttemptedFocus = false; 

    // Do something with the image 
}