Добавил библиотеку zbar, она медленно, но верно распознает код на серебрянной карточке. Нужно настроить конфиг.

.gitignore

@@ -3,7 +3,9 @@
 .idea
 .packages
 .pub/
+.gradle/
 build/
+gen/
 ios/.generated/
 packages
 pubspec.lock

android.iml

@@ -1,12 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<module type="JAVA_MODULE" version="4">
-  <component name="NewModuleRootManager" inherit-compiler-output="true">
-    <exclude-output />
-    <content url="file://$MODULE_DIR$/android">
-      <sourceFolder url="file://$MODULE_DIR$/android/app/src/main/java" isTestSource="false" />
-    </content>
-    <orderEntry type="jdk" jdkName="Android API 25 Platform" jdkType="Android SDK" />
-    <orderEntry type="sourceFolder" forTests="false" />
-    <orderEntry type="library" name="Flutter for Android" level="project" />
-  </component>
-</module>

android/app/build.gradle

@@ -36,6 +36,10 @@ android {
             signingConfig signingConfigs.debug
         }
     }
+
+    sourceSets.main {
+        jniLibs.srcDir 'jniLibs'
+    }
 }
 
 flutter {
@@ -43,6 +47,7 @@ flutter {
 }
 
 dependencies {
+    compile fileTree(dir: 'libs', include: ['*.jar'])
     androidTestCompile 'com.android.support:support-annotations:25.4.0'
     androidTestCompile 'com.android.support.test:runner:0.5'
     androidTestCompile 'com.android.support.test:rules:0.5'

android/app/src/main/AndroidManifest.xml

@@ -10,6 +10,7 @@
          to allow setting breakpoints, to provide hot reload, etc.
     -->
     <uses-permission android:name="android.permission.INTERNET"/>
+    <uses-permission android:name="android.permission.CAMERA"/>
 
     <!-- io.flutter.app.FlutterApplication is an android.app.Application that
          calls FlutterMain.startInitialization(this); in its onCreate method.

android/app/src/main/java/com/yourcompany/checker/CameraActivity.java

@@ -1,17 +0,0 @@
-package com.yourcompany.checker;
-
-import android.app.Activity;
-import android.content.Intent;
-import android.os.Bundle;
-
-import com.yourcompany.checker.R;
-
-public class CameraActivity extends Activity {
-
-    @Override
-    public void onCreate(Bundle savedInstanceState) {
-        super.onCreate(savedInstanceState);
-        setContentView(R.layout.a_scanner);
-    }
-
-}

android/app/src/main/java/com/yourcompany/checker/activity/CameraActivity.java

@@ -0,0 +1,152 @@
+package com.yourcompany.checker;
+
+import android.app.Activity;
+import android.content.pm.ActivityInfo;
+import android.os.Bundle;
+import android.os.Handler;
+import android.util.Log;
+
+import android.view.View;
+import android.view.View.OnClickListener;
+import android.view.Window;
+import android.widget.FrameLayout;
+import android.widget.Button;
+
+import android.hardware.Camera;
+import android.hardware.Camera.PreviewCallback;
+import android.hardware.Camera.AutoFocusCallback;
+import android.hardware.Camera.Parameters;
+import android.hardware.Camera.Size;
+
+import android.widget.TextView;
+import android.widget.Toast;
+import android.view.SurfaceView;
+import android.view.SurfaceHolder;
+import android.graphics.ImageFormat;
+import net.sourceforge.zbar.ImageScanner;
+import net.sourceforge.zbar.Image;
+import net.sourceforge.zbar.Symbol;
+import net.sourceforge.zbar.SymbolSet;
+import net.sourceforge.zbar.Config;
+
+import com.yourcompany.checker.R;
+import com.yourcompany.checker.view.CameraPreview;
+
+public class CameraActivity extends Activity {
+
+    private Camera mCamera;
+    private SurfaceView mPreview;
+    private Handler autoFocusHandler;
+
+    ImageScanner scanner;
+
+    private boolean barcodeScanned = false;
+    private boolean previewing = true;
+
+    static {
+        System.loadLibrary("iconv");
+    }
+
+    public void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        setContentView(R.layout.a_scanner);
+        setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
+
+        autoFocusHandler = new Handler();
+        mCamera = getCameraInstance();
+
+        /* Instance barcode scanner */
+        scanner = new ImageScanner();
+        scanner.setConfig(0, Config.X_DENSITY, 3);
+        scanner.setConfig(0, Config.Y_DENSITY, 3);
+
+        mPreview = (SurfaceView) findViewById(R.id.cameraPreview);
+
+        SurfaceHolder holder = mPreview.getHolder();
+        holder.addCallback(new SurfaceHolder.Callback() {
+            @Override
+            public void surfaceCreated(SurfaceHolder holder) {
+                try {
+                    mCamera.setPreviewDisplay(holder);
+                    mCamera.startPreview();
+                    mCamera.setPreviewCallback(previewCallback);
+                    mCamera.autoFocus(autoFocusCB);
+                } catch (Exception e) {
+                    e.printStackTrace();
+                }
+            }
+
+            @Override
+            public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
+                mCamera.setDisplayOrientation(270);
+            }
+
+            @Override
+            public void surfaceDestroyed(SurfaceHolder holder) {
+
+            }
+        });
+    }
+
+    public void onPause() {
+        super.onPause();
+        releaseCamera();
+    }
+
+    /** A safe way to get an instance of the Camera object. */
+    public static Camera getCameraInstance(){
+        Camera c = null;
+        try {
+            c = Camera.open();
+        } catch (Exception e){
+        }
+        return c;
+    }
+
+    private void releaseCamera() {
+        if (mCamera != null) {
+            previewing = false;
+            mCamera.setPreviewCallback(null);
+            mCamera.release();
+            mCamera = null;
+        }
+    }
+
+    private Runnable doAutoFocus = new Runnable() {
+        public void run() {
+            if (previewing)
+                mCamera.autoFocus(autoFocusCB);
+        }
+    };
+
+    PreviewCallback previewCallback = new PreviewCallback() {
+        public void onPreviewFrame(byte[] data, Camera camera) {
+            Camera.Parameters parameters = camera.getParameters();
+            Size size = parameters.getPreviewSize();
+
+            Image barcode = new Image(size.width, size.height, "Y800");
+            barcode.setData(data);
+
+            int result = scanner.scanImage(barcode);
+
+            if (result != 0) {
+                previewing = false;
+                mCamera.setPreviewCallback(null);
+                mCamera.stopPreview();
+
+                SymbolSet syms = scanner.getResults();
+                for (Symbol sym : syms) {
+                    barcodeScanned = true;
+                    Toast.makeText(CameraActivity.this, sym.getData(), Toast.LENGTH_SHORT).show();
+                }
+            }
+        }
+    };
+
+    // Mimic continuous auto-focusing
+    AutoFocusCallback autoFocusCB = new AutoFocusCallback() {
+        public void onAutoFocus(boolean success, Camera camera) {
+            autoFocusHandler.postDelayed(doAutoFocus, 1000);
+        }
+    };
+}

android/app/src/main/java/com/yourcompany/checker/activity/MainActivity.java

@@ -32,7 +32,7 @@ public class MainActivity extends FlutterActivity {
     }
 
     public void startScanner() {
-      
+
     }
 
 }

android/app/src/main/java/com/yourcompany/checker/view/CameraPreview.java

@@ -0,0 +1,85 @@
+package com.yourcompany.checker.view;
+
+import java.io.IOException;
+
+import android.app.Activity;
+import android.os.Bundle;
+
+import android.util.Log;
+
+import android.view.View;
+import android.view.Surface;
+import android.view.SurfaceView;
+import android.view.SurfaceHolder;
+
+import android.content.Context;
+
+import android.hardware.Camera;
+import android.hardware.Camera.PreviewCallback;
+import android.hardware.Camera.AutoFocusCallback;
+import android.hardware.Camera.Parameters;
+
+public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
+
+    private SurfaceHolder mHolder;
+    private Camera mCamera;
+    private PreviewCallback previewCallback;
+    private AutoFocusCallback autoFocusCallback;
+
+    public CameraPreview(Context context, Camera camera,
+                         PreviewCallback previewCb,
+                         AutoFocusCallback autoFocusCb) {
+        super(context);
+        mCamera = camera;
+        previewCallback = previewCb;
+        autoFocusCallback = autoFocusCb;
+        mHolder = getHolder();
+        mHolder.addCallback(this);
+
+        // deprecated setting, but required on Android versions prior to 3.0
+        mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
+    }
+
+    public void surfaceCreated(SurfaceHolder holder) {
+        // The Surface has been created, now tell the camera where to draw the preview.
+        try {
+            mCamera.setPreviewDisplay(holder);
+        } catch (IOException e) {
+            Log.d("DBG", "Error setting camera preview: " + e.getMessage());
+        }
+    }
+
+    public void surfaceDestroyed(SurfaceHolder holder) {
+        // Camera preview released in activity
+    }
+
+    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
+        /*
+         * If your preview can change or rotate, take care of those events here.
+         * Make sure to stop the preview before resizing or reformatting it.
+         */
+        if (mHolder.getSurface() == null){
+          // preview surface does not exist
+          return;
+        }
+
+        // stop preview before making changes
+        try {
+            mCamera.stopPreview();
+        } catch (Exception e){
+          // ignore: tried to stop a non-existent preview
+        }
+
+        try {
+            // Hard code camera surface rotation 90 degs to match Activity view in portrait
+            mCamera.setDisplayOrientation(90);
+
+            mCamera.setPreviewDisplay(mHolder);
+            mCamera.setPreviewCallback(previewCallback);
+            mCamera.startPreview();
+            mCamera.autoFocus(autoFocusCallback);
+        } catch (Exception e){
+            Log.d("DBG", "Error starting camera preview: " + e.getMessage());
+        }
+    }
+}

android/app/src/main/res/layout/a_scanner.xml

@@ -1,14 +1,14 @@
 <?xml version="1.0" encoding="utf-8"?>
 <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
-                xmlns:app="http://schemas.android.com/apk/res-auto"
-                android:id="@+id/rootLayout"
-                android:background="@android:color/white"
-                android:layout_width="match_parent"
-                android:layout_height="match_parent">
+             xmlns:app="http://schemas.android.com/apk/res-auto"
+             android:id="@+id/rootLayout"
+             android:background="@android:color/white"
+             android:layout_width="match_parent"
+             android:layout_height="match_parent">
+
+    <SurfaceView android:id="@+id/cameraPreview"
+                 android:layout_width="match_parent"
+                 android:layout_height="match_parent"/>
 
-  <TextView android:layout_width="match_parent"
-            android:layout_height="match_parent"
-            android:gravity="center"
-            android:text="Asdf"/>
 
 </FrameLayout>

checker.iml

@@ -1,15 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<module type="FLUTTER_MODULE_TYPE" version="4">
-  <component name="NewModuleRootManager" inherit-compiler-output="true">
-    <exclude-output />
-    <content url="file://$MODULE_DIR$">
-      <excludeFolder url="file://$MODULE_DIR$/.idea" />
-      <excludeFolder url="file://$MODULE_DIR$/.pub" />
-      <excludeFolder url="file://$MODULE_DIR$/build" />
-      <excludeFolder url="file://$MODULE_DIR$/packages" />
-    </content>
-    <orderEntry type="sourceFolder" forTests="false" />
-    <orderEntry type="library" name="Dart Packages" level="project" />
-    <orderEntry type="library" name="Dart SDK" level="project" />
-  </component>
-</module>

checker_android.iml

@@ -1,12 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<module type="JAVA_MODULE" version="4">
-  <component name="NewModuleRootManager" inherit-compiler-output="true">
-    <exclude-output />
-    <content url="file://$MODULE_DIR$/android">
-      <sourceFolder url="file://$MODULE_DIR$/android/app/src/main/java" isTestSource="false" />
-    </content>
-    <orderEntry type="jdk" jdkName="Android API 25 Platform" jdkType="Android SDK" />
-    <orderEntry type="sourceFolder" forTests="false" />
-    <orderEntry type="library" name="Flutter for Android" level="project" />
-  </component>
-</module>