add a couple extra checks to prevent crashing

app/src/main/java/com/simplemobiletools/camera/MainActivity.java

@@ -135,19 +135,24 @@ public class MainActivity extends AppCompatActivity implements SensorEventListen
             return;
         }
 
-        disableFlash();
-        hideTimer();
         if (currCamera == Camera.CameraInfo.CAMERA_FACING_BACK) {
             currCamera = Camera.CameraInfo.CAMERA_FACING_FRONT;
-            toggleCameraBtn.setImageResource(R.mipmap.camera_rear);
         } else {
             currCamera = Camera.CameraInfo.CAMERA_FACING_BACK;
-            toggleCameraBtn.setImageResource(R.mipmap.camera_front);
         }
 
-        disableFlash();
+        int newIconId = R.mipmap.camera_front;
         preview.releaseCamera();
-        preview.setCamera(currCamera);
+        if (preview.setCamera(currCamera)) {
+            if (currCamera == Camera.CameraInfo.CAMERA_FACING_BACK) {
+                newIconId = R.mipmap.camera_rear;
+            }
+            toggleCameraBtn.setImageResource(newIconId);
+            disableFlash();
+            hideTimer();
+        } else {
+            Utils.showToast(getApplicationContext(), R.string.camera_switch_error);
+        }
     }
 
     @OnClick(R.id.toggle_flash)
@@ -239,11 +244,14 @@ public class MainActivity extends AppCompatActivity implements SensorEventListen
     }
 
     private void initVideoButtons() {
+        if (preview.initRecorder()) {
             final Resources res = getResources();
             togglePhotoVideoBtn.setImageDrawable(res.getDrawable(R.mipmap.photo));
             shutterBtn.setImageDrawable(res.getDrawable(R.mipmap.video_rec));
-        preview.initRecorder();
             toggleCameraBtn.setVisibility(View.VISIBLE);
+        } else {
+            Utils.showToast(getApplicationContext(), R.string.video_mode_error);
+        }
     }
 
     private void hideNavigationBarIcons() {
@@ -286,7 +294,7 @@ public class MainActivity extends AppCompatActivity implements SensorEventListen
             toggleCameraBtn.setVisibility(View.INVISIBLE);
         }
 
-        preview.setCamera(currCamera);
+        if (preview.setCamera(currCamera)) {
             hideNavigationBarIcons();
 
             if (sensorManager != null) {
@@ -297,6 +305,9 @@ public class MainActivity extends AppCompatActivity implements SensorEventListen
             if (!isInPhotoMode) {
                 initVideoButtons();
             }
+        } else {
+            Utils.showToast(getApplicationContext(), R.string.camera_switch_error);
+        }
     }
 
     @Override
@@ -371,4 +382,11 @@ public class MainActivity extends AppCompatActivity implements SensorEventListen
             finish();
         }
     }
+
+    @Override
+    protected void onDestroy() {
+        super.onDestroy();
+        if (preview != null)
+            preview.releaseCamera();
+    }
 }

app/src/main/java/com/simplemobiletools/camera/Preview.java

@@ -72,7 +72,7 @@ public class Preview extends ViewGroup implements SurfaceHolder.Callback, View.O
         curVideoPath = "";
     }
 
-    public void setCamera(int cameraId) {
+    public boolean setCamera(int cameraId) {
         currCameraId = cameraId;
         Camera newCamera;
         try {
@@ -82,11 +82,11 @@ public class Preview extends ViewGroup implements SurfaceHolder.Callback, View.O
             Utils.showToast(getContext(), R.string.camera_open_error);
             Log.e(TAG, "setCamera open " + e.getMessage());
             callback.setIsCameraAvailable(false);
-            return;
+            return false;
         }
 
         if (camera == newCamera) {
-            return;
+            return false;
         }
 
         releaseCamera();
@@ -109,6 +109,7 @@ public class Preview extends ViewGroup implements SurfaceHolder.Callback, View.O
                     camera.setPreviewDisplay(surfaceHolder);
                 } catch (IOException e) {
                     Log.e(TAG, "setCamera setPreviewDisplay " + e.getMessage());
+                    return false;
                 }
                 setupPreview();
             }
@@ -119,6 +120,8 @@ public class Preview extends ViewGroup implements SurfaceHolder.Callback, View.O
         if (isVideoMode) {
             initRecorder();
         }
+
+        return true;
     }
 
     public void setTargetUri(Uri uri) {
@@ -455,12 +458,14 @@ public class Preview extends ViewGroup implements SurfaceHolder.Callback, View.O
     }
 
     // VIDEO RECORDING
-    public void initRecorder() {
+    public boolean initRecorder() {
         if (camera == null || recorder != null || !isSurfaceCreated)
-            return;
+            return false;
 
-        camera.lock();
         final Camera.Size preferred = parameters.getPreferredPreviewSizeForVideo();
+        if (preferred == null)
+            return false;
+
         parameters.setPreviewSize(preferred.width, preferred.height);
         camera.setParameters(parameters);
 
@@ -474,7 +479,7 @@ public class Preview extends ViewGroup implements SurfaceHolder.Callback, View.O
         curVideoPath = Utils.getOutputMediaFile(getContext(), false);
         if (curVideoPath.isEmpty()) {
             Utils.showToast(getContext(), R.string.video_creating_error);
-            return;
+            return false;
         }
 
         final Camera.Size videoSize = getOptimalVideoSize();
@@ -495,7 +500,9 @@ public class Preview extends ViewGroup implements SurfaceHolder.Callback, View.O
             Utils.showToast(getContext(), R.string.video_setup_error);
             Log.e(TAG, "initRecorder " + e.getMessage());
             releaseCamera();
+            return false;
         }
+        return true;
     }
 
     public boolean toggleRecording() {

app/src/main/res/values/strings.xml

@@ -5,8 +5,10 @@
     <string name="video_creating_error">An error occurred at creating the video file</string>
     <string name="video_saving_error">An error occurred at saving the video file</string>
     <string name="video_setup_error">An error occurred at setting up the recorder</string>
+    <string name="video_mode_error">Switching to video mode failed</string>
     <string name="video_directory">Simple Videos</string>
     <string name="photo_directory">Simple Photos</string>
+    <string name="camera_switch_error">Switching camera failed</string>
     <string name="no_permissions">Not much to do without accessing your camera and storage</string>
     <string name="no_audio_permissions">We need the audio permission for recording videos</string>