Android 开发技巧——五分钟实现二维码识别

阅读 3926
收藏 133
2016-06-11
原文链接:blog.csdn.net

二维码扫描解析现在已经成为一个综合型APP所不可或缺的一个功能了,有很多入门的开发者或许会苦恼二维码识别肯定是得会图像分析技术呀,难道还得学opencv吗?NO,Google早已想到这一点,因此也开源了二维码扫描、生成的代码——zxing,ZXing是一个开源Java类库用于解析多种格式的1D/2D条形码。目标是能够对QR编码、Data Matrix、UPC的1D条形码进行解码。 其提供了多种平台下的客户端包括:J2ME、J2SE和Android。  

官方github:https://github.com/zxing/zxing/tree/zxing-3.0.0

而官方提供的工程足足有100+M,那作为Android开发者,我们不可能依赖所有的代码,因此在这篇博文中,我仅仅介绍二维码的扫描以及识别,由于二维码只是其中的一部分功能,因此我在慕课上寻了一个module,大家只需要在github上download下来依赖即可:https://github.com/weizainiunai/libzxing,至于怎么依赖我会在接下来的博文中解释。

那么做一个二维码扫描APP,肯定得先了解二维码是什么东西?二维条码/二维码(2-dimensional bar code)是用某种特定的几何图形按一定规律在平面(二维方向上)分布的黑白相间的图形记录数据符号信息的;在代码编制上巧妙地利用构成计算机内部逻辑基础的“0”、“1”比特流的概念,使用若干个与二进制相对应的几何形体来表示文字数值信息,通过图象输入设备或光电扫描设备自动识读以实现信息自动处理:它具有条码技术的一些共性:每种码制有其特定的字符集;每个字符占有一定的宽度;具有一定的校验功能等。同时还具有对不同行的信息自动识别功能、及处理图形旋转变化点。更具体的大家可以去百度百科上去了解。


首先新建一个工程



打开选择之前所下载好的lib project进行依赖:




依赖好之后便是编写我们的界面:acitivity_main.xml:
xml version="1.0" encoding="utf-8"?>
xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">



            android:id="@+id/btn_scan"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="scan"
        />

            android:id="@+id/tv_result"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="result"
        />


那界面写好之后,我们需要调用哪些方法才能实现二维码的识别功能呢? 之前我们所依赖的工程中有一个CaptureActivity.java文件,而这个activity便是二维码识别功能的执行以及回调:
/**
 * This activity opens the camera and does the actual scanning on a background
 * thread. It draws a viewfinder to help the user place the barcode correctly,
 * shows feedback as the image processing is happening, and then overlays the
 * results when a scan is successful.
 *
 * @author dswitkin@google.com (Daniel Switkin)
 * @author Sean Owen
 */
public final class CaptureActivity extends Activity implements SurfaceHolder.Callback {

    private static final String TAG = CaptureActivity.class.getSimpleName();

    private CameraManager cameraManager;
    private CaptureActivityHandler handler;
    private InactivityTimer inactivityTimer;
    private BeepManager beepManager;

    private SurfaceView scanPreview = null;
    private RelativeLayout scanContainer;
    private RelativeLayout scanCropView;
    private ImageView scanLine;

    private Rect mCropRect = null;
    private boolean isHasSurface = false;

    public Handler getHandler() {
        return handler;
    }

    public CameraManager getCameraManager() {
        return cameraManager;
    }

    @Override
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);

        Window window = getWindow();
        window.addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
        setContentView(R.layout.activity_capture);

        scanPreview = (SurfaceView) findViewById(R.id.capture_preview);
        scanContainer = (RelativeLayout) findViewById(R.id.capture_container);
        scanCropView = (RelativeLayout) findViewById(R.id.capture_crop_view);
        scanLine = (ImageView) findViewById(R.id.capture_scan_line);

        inactivityTimer = new InactivityTimer(this);
        beepManager = new BeepManager(this);

        TranslateAnimation animation = new TranslateAnimation(Animation.RELATIVE_TO_PARENT, 0.0f, Animation
                .RELATIVE_TO_PARENT, 0.0f, Animation.RELATIVE_TO_PARENT, 0.0f, Animation.RELATIVE_TO_PARENT,
                0.9f);
        animation.setDuration(4500);
        animation.setRepeatCount(-1);
        animation.setRepeatMode(Animation.RESTART);
        scanLine.startAnimation(animation);
    }

    @Override
    protected void onResume() {
        super.onResume();

        // CameraManager must be initialized here, not in onCreate(). This is
        // necessary because we don't
        // want to open the camera driver and measure the screen size if we're
        // going to show the help on
        // first launch. That led to bugs where the scanning rectangle was the
        // wrong size and partially
        // off screen.
        cameraManager = new CameraManager(getApplication());

        handler = null;

        if (isHasSurface) {
            // The activity was paused but not stopped, so the surface still
            // exists. Therefore
            // surfaceCreated() won't be called, so init the camera here.
            initCamera(scanPreview.getHolder());
        } else {
            // Install the callback and wait for surfaceCreated() to init the
            // camera.
            scanPreview.getHolder().addCallback(this);
        }

        inactivityTimer.onResume();
    }

    @Override
    protected void onPause() {
        if (handler != null) {
            handler.quitSynchronously();
            handler = null;
        }
        inactivityTimer.onPause();
        beepManager.close();
        cameraManager.closeDriver();
        if (!isHasSurface) {
            scanPreview.getHolder().removeCallback(this);
        }
        super.onPause();
    }

    @Override
    protected void onDestroy() {
        inactivityTimer.shutdown();
        super.onDestroy();
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        if (holder == null) {
            Log.e(TAG, "*** WARNING *** surfaceCreated() gave us a null surface!");
        }
        if (!isHasSurface) {
            isHasSurface = true;
            initCamera(holder);
        }
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        isHasSurface = false;
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {

    }

    /**
     * A valid barcode has been found, so give an indication of success and show
     * the results.
     *
     * @param rawResult The contents of the barcode.
     * @param bundle    The extras
     */
    public void handleDecode(Result rawResult, Bundle bundle) {
        inactivityTimer.onActivity();
        beepManager.playBeepSoundAndVibrate();

        Intent resultIntent = new Intent();
        bundle.putInt("width", mCropRect.width());
        bundle.putInt("height", mCropRect.height());
        bundle.putString("result", rawResult.getText());
        resultIntent.putExtras(bundle);
        this.setResult(RESULT_OK, resultIntent);
        CaptureActivity.this.finish();
    }

    private void initCamera(SurfaceHolder surfaceHolder) {
        if (surfaceHolder == null) {
            throw new IllegalStateException("No SurfaceHolder provided");
        }
        if (cameraManager.isOpen()) {
            Log.w(TAG, "initCamera() while already open -- late SurfaceView callback?");
            return;
        }
        try {
            cameraManager.openDriver(surfaceHolder);
            // Creating the handler starts the preview, which can also throw a
            // RuntimeException.
            if (handler == null) {
                handler = new CaptureActivityHandler(this, cameraManager, DecodeThread.ALL_MODE);
            }

            initCrop();
        } catch (IOException ioe) {
            Log.w(TAG, ioe);
            displayFrameworkBugMessageAndExit();
        } catch (RuntimeException e) {
            // Barcode Scanner has seen crashes in the wild of this variety:
            // java.?lang.?RuntimeException: Fail to connect to camera service
            Log.w(TAG, "Unexpected error initializing camera", e);
            displayFrameworkBugMessageAndExit();
        }
    }

    private void displayFrameworkBugMessageAndExit() {
        // camera error
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle(getString(R.string.app_name));
        builder.setMessage("Camera error");
        builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {

            @Override
            public void onClick(DialogInterface dialog, int which) {
                finish();
            }

        });
        builder.setOnCancelListener(new DialogInterface.OnCancelListener() {

            @Override
            public void onCancel(DialogInterface dialog) {
                finish();
            }
        });
        builder.show();
    }

    public void restartPreviewAfterDelay(long delayMS) {
        if (handler != null) {
            handler.sendEmptyMessageDelayed(R.id.restart_preview, delayMS);
        }
    }

    public Rect getCropRect() {
        return mCropRect;
    }

    /**
     * 初始化截取的矩形区域
     */
    private void initCrop() {
        int cameraWidth = cameraManager.getCameraResolution().y;
        int cameraHeight = cameraManager.getCameraResolution().x;

        /** 获取布局中扫描框的位置信息 */
        int[] location = new int[2];
        scanCropView.getLocationInWindow(location);

        int cropLeft = location[0];
        int cropTop = location[1] - getStatusBarHeight();

        int cropWidth = scanCropView.getWidth();
        int cropHeight = scanCropView.getHeight();

        /** 获取布局容器的宽高 */
        int containerWidth = scanContainer.getWidth();
        int containerHeight = scanContainer.getHeight();

        /** 计算最终截取的矩形的左上角顶点x坐标 */
        int x = cropLeft * cameraWidth / containerWidth;
        /** 计算最终截取的矩形的左上角顶点y坐标 */
        int y = cropTop * cameraHeight / containerHeight;

        /** 计算最终截取的矩形的宽度 */
        int width = cropWidth * cameraWidth / containerWidth;
        /** 计算最终截取的矩形的高度 */
        int height = cropHeight * cameraHeight / containerHeight;

        /** 生成最终的截取的矩形 */
        mCropRect = new Rect(x, y, width + x, height + y);
    }

    private int getStatusBarHeight() {
        try {
            Class c = Class.forName("com.android.internal.R$dimen");
            Object obj = c.newInstance();
            Field field = c.getField("status_bar_height");
            int x = Integer.parseInt(field.get(obj).toString());
            return getResources().getDimensionPixelSize(x);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return 0;
    }
}

如果你需要学习二维码识别更底层的代码,这里面可是有不少的干货哦,那对我们使用者来说,我们只需要了解这个class的回调方法就行,返回给我们什么参数?key是多少?
/**
 * A valid barcode has been found, so give an indication of success and show
 * the results.
 *
 * @param rawResult The contents of the barcode.
 * @param bundle    The extras
 */
public void handleDecode(Result rawResult, Bundle bundle) {
    inactivityTimer.onActivity();
    beepManager.playBeepSoundAndVibrate();

    Intent resultIntent = new Intent();
    bundle.putInt("width", mCropRect.width());
    bundle.putInt("height", mCropRect.height());
    bundle.putString("result", rawResult.getText());
    resultIntent.putExtras(bundle);
    this.setResult(RESULT_OK, resultIntent);
    CaptureActivity.this.finish();
}

在这其中我们可以看见,它为我们回调了三个参数,分别是宽,高以及字符串(识别出来的内容),而我们,只需要result这个参数,那么知道这些,接下来便是主要代码的编写:EntrenceActivity.java
public class EntrenceActivity extends AppCompatActivity {
    private Button mBtnScanner;
    private TextView mTvResult;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_entrence);

        initview();

    }

    private void initview() {
        mBtnScanner = (Button) findViewById(R.id.btn_scan);
        mTvResult = (TextView) findViewById(R.id.tv_result);

        mBtnScanner.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                startActivityForResult(new Intent(EntrenceActivity.this , CaptureActivity.class) , 0);

            }
        });

    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if (resultCode == RESULT_OK){
            Bundle bundle = data.getExtras();
            String result = bundle.getString("result");
            mTvResult.setText(result);
        }

    }
}

了解完这些,大家大概也知道了如何用zxing实现一个简单的二维码识别app了,当然,我们并不需要在自己的主工程中添加相关的相机等权限,因为在谷歌提供给我们的module中已经将其添加进去了,所以大家可以放心的使用,看看是不是真的5分钟实现二维码扫描了呢~~,如果觉得还行,请给博主点赞哦!!

评论