修复部分机型Activity不可见时，Camera预览失败bug

app/src/main/AndroidManifest.xml

@@ -7,6 +7,7 @@
     <!--全局异常检测，需添加-->
     <!--android:name=".application.MyApplication"-->
     <application
+        android:name=".application.MyApplication"
         android:allowBackup="true"
         android:icon="@mipmap/ic_launcher"
         android:label="@string/app_name"

app/src/main/java/com/jiangdg/usbcamera/view/USBCameraActivity.java

@@ -62,6 +62,7 @@ public class USBCameraActivity extends AppCompatActivity implements CameraDialog
     private CameraViewInterface mUVCCameraView;
 
     private boolean isRequest;
+    private boolean isPreview;
 
     /**
      * USB设备事件监听器
@@ -99,6 +100,9 @@ public class USBCameraActivity extends AppCompatActivity implements CameraDialog
         public void onConnectDev(UsbDevice device,boolean isConnected) {
             if(! isConnected) {
                 showShortMsg("连接失败，请检查分辨率参数是否正确");
+                isPreview = false;
+            }else{
+                isPreview = true;
             }
         }
 
@@ -125,10 +129,20 @@ public class USBCameraActivity extends AppCompatActivity implements CameraDialog
     @Override
     protected void onStart() {
         super.onStart();
+        if(mUSBManager == null)
+            return;
         // 注册USB事件广播监听器
-        if(mUSBManager != null){
         mUSBManager.registerUSB();
+        if(!isPreview && mUSBManager.isCameraOpened()) {
+            mUSBManager.startPreview(mUVCCameraView, new AbstractUVCCameraHandler.OnPreViewResultListener() {
+                @Override
+                public void onPreviewResult(boolean result) {
+
                 }
+            });
+            isPreview = true;
+        }
+
     }
 
     @Override
@@ -138,6 +152,10 @@ public class USBCameraActivity extends AppCompatActivity implements CameraDialog
         if(mUSBManager != null){
             mUSBManager.unregisterUSB();
         }
+        if(isPreview && mUSBManager.isCameraOpened()) {
+            mUSBManager.stopPreview();
+            isPreview = false;
+        }
     }
 
     @OnClick({ R.id.btn_contrast,R.id.btn_brightness,R.id.btn_capture_pic, R.id.btn_rec_video,R.id.btn_update_resolution,R.id.btn_restart_camera})

libusbcamera/src/main/java/com/jiangdg/usbcamera/USBCameraManager.java

@@ -338,6 +338,13 @@ public class USBCameraManager{
         }
     }
 
+    // 停止预览
+    public void stopPreview() {
+        if(mCameraHandler != null){
+            mCameraHandler.stopPreview();
+        }
+    }
+
     // Camera对焦
     public void startCameraFoucs(){
         if(mCameraHandler != null){