zxing二维码扫描的流程简析（Android版）

目前市面上二维码的扫描似乎用开源google的zxing比较多，接下去以2.2版本做一个简析吧，勿喷。。。

下载下来后定位两个文件夹，core和android，core是一些核心的库，android是针对android的一些代码。

zxing二维码扫描的流程简析（Android版）_第1张图片

我们先看核心库，在package com.google.zxing中的一些生成二维码的类关系

zxing二维码扫描的流程简析（Android版）_第2张图片

接口Writer里面有两个encode的重载函数，不同的格式的二维码有各自的类实现了Writer接口，MultiformatWriter类比较特殊，根据代码的注释可见其其实是个工厂类，根据BarcodeFormat实例化不同的Writer，然后最终调用各自的Encode.encode()方法

 1 public final class MultiFormatWriter implements Writer { 2  3   @Override 4   public BitMatrix encode(String contents, 5                           BarcodeFormat format, 6                           int width, 7                           int height) throws WriterException { 8     return encode(contents, format, width, height, null); 9   }10 11   @Override12   public BitMatrix encode(String contents,13                           BarcodeFormat format,14                           int width, int height,15                           Map<EncodeHintType,?> hints) throws WriterException {16 17     Writer writer;18     switch (format) {19       case EAN_8:20         writer = new EAN8Writer();21         break;22       case EAN_13:23         writer = new EAN13Writer();24         break;25       case UPC_A:26         writer = new UPCAWriter();27         break;28       case QR_CODE:29         writer = new QRCodeWriter();30         break;31       case CODE_39:32         writer = new Code39Writer();33         break;34       case CODE_128:35         writer = new Code128Writer();36         break;37       case ITF:38         writer = new ITFWriter();39         break;40       case PDF_417:41         writer = new PDF417Writer();42         break;43       case CODABAR:44         writer = new CodaBarWriter();45         break;46       case DATA_MATRIX:47         writer = new DataMatrixWriter();48         break;49       case AZTEC:50         writer = new AztecWriter();51         break;52       default:53         throw new IllegalArgumentException("No encoder available for format " + format);54     }55     return writer.encode(contents, format, width, height, hints);56   }57 58 }

然后看解析二维码的类结构

zxing二维码扫描的流程简析（Android版）_第3张图片

关键就是这个MultiformatReader，里面聚合了多个reader,并且根据客户端设置的DecodeHintType值，确定添加reader以及添加reader的顺序，最后调用reader.decode方法

  1 public final class MultiFormatReader implements Reader {  2   3   private Map<DecodeHintType,?> hints;  4   private Reader[] readers;  5   6   @Override  7   public Result decode(BinaryBitmap image) throws NotFoundException {  8     setHints(null);  9     return decodeInternal(image); 10   } 11  12   @Override 13   public Result decode(BinaryBitmap image, Map<DecodeHintType,?> hints) throws NotFoundException { 14     setHints(hints); 15     return decodeInternal(image); 16   } 17  18   public Result decodeWithState(BinaryBitmap image) throws NotFoundException { 19     // Make sure to set up the default state so we don't crash 20     if (readers == null) { 21       setHints(null); 22     } 23     return decodeInternal(image); 24   } 25  26   public void setHints(Map<DecodeHintType,?> hints) {//根据设置的hint来设置reader 27     this.hints = hints; 28  29     boolean tryHarder = hints != null && hints.containsKey(DecodeHintType.TRY_HARDER); 30     @SuppressWarnings("unchecked") 31     Collection<BarcodeFormat> formats = 32         hints == null ? null : (Collection<BarcodeFormat>) hints.get(DecodeHintType.POSSIBLE_FORMATS); 33     Collection<Reader> readers = new ArrayList<Reader>(); 34     if (formats != null) { 35       boolean addOneDReader = 36           formats.contains(BarcodeFormat.UPC_A) || 37           formats.contains(BarcodeFormat.UPC_E) || 38           formats.contains(BarcodeFormat.EAN_13) || 39           formats.contains(BarcodeFormat.EAN_8) || 40           formats.contains(BarcodeFormat.CODABAR) || 41           formats.contains(BarcodeFormat.CODE_39) || 42           formats.contains(BarcodeFormat.CODE_93) || 43           formats.contains(BarcodeFormat.CODE_128) || 44           formats.contains(BarcodeFormat.ITF) || 45           formats.contains(BarcodeFormat.RSS_14) || 46           formats.contains(BarcodeFormat.RSS_EXPANDED); 47       // Put 1D readers upfront in "normal" mode 48       if (addOneDReader && !tryHarder) { 49         readers.add(new MultiFormatOneDReader(hints)); 50       } 51       if (formats.contains(BarcodeFormat.QR_CODE)) { 52         readers.add(new QRCodeReader()); 53       } 54       if (formats.contains(BarcodeFormat.DATA_MATRIX)) { 55         readers.add(new DataMatrixReader()); 56       } 57       if (formats.contains(BarcodeFormat.AZTEC)) { 58         readers.add(new AztecReader()); 59       } 60       if (formats.contains(BarcodeFormat.PDF_417)) { 61          readers.add(new PDF417Reader()); 62       } 63       if (formats.contains(BarcodeFormat.MAXICODE)) { 64          readers.add(new MaxiCodeReader()); 65       } 66       // At end in "try harder" mode 67       if (addOneDReader && tryHarder) { 68         readers.add(new MultiFormatOneDReader(hints)); 69       } 70     } 71     if (readers.isEmpty()) { 72       if (!tryHarder) { 73         readers.add(new MultiFormatOneDReader(hints)); 74       } 75  76       readers.add(new QRCodeReader()); 77       readers.add(new DataMatrixReader()); 78       readers.add(new AztecReader()); 79       readers.add(new PDF417Reader()); 80       readers.add(new MaxiCodeReader()); 81  82       if (tryHarder) { 83         readers.add(new MultiFormatOneDReader(hints)); 84       } 85     } 86     this.readers = readers.toArray(new Reader[readers.size()]); 87   } 88  89   @Override 90   public void reset() { 91     if (readers != null) { 92       for (Reader reader : readers) { 93         reader.reset(); 94       } 95     } 96   } 97  98   private Result decodeInternal(BinaryBitmap image) throws NotFoundException {//最终都调用这个方法 99     if (readers != null) {100       for (Reader reader : readers) {101         try {102           return reader.decode(image, hints);103         } catch (ReaderException re) {104           // continue105         }106       }107     }108     throw NotFoundException.getNotFoundInstance();109   }110 111 }

DecodeHintType的语法比较有意思，还在理解中

 1 public enum DecodeHintType { 2  3   /** 4    * Unspecified, application-specific hint. Maps to an unspecified {@link Object}. 5    */ 6  OTHER(Object.class), 7  8   /** 9    * Image is a pure monochrome image of a barcode. Doesn't matter what it maps to;10    * use {@link Boolean#TRUE}.11    */12   PURE_BARCODE(Void.class),13 14   /**15    * Image is known to be of one of a few possible formats.16    * Maps to a {@link List} of {@link BarcodeFormat}s.17    */18   POSSIBLE_FORMATS(List.class),19 20   /**21    * Spend more time to try to find a barcode; optimize for accuracy, not speed.22    * Doesn't matter what it maps to; use {@link Boolean#TRUE}.23    */24   TRY_HARDER(Void.class),25 26   /**27    * Specifies what character encoding to use when decoding, where applicable (type String)28    */29   CHARACTER_SET(String.class),30 31   /**32    * Allowed lengths of encoded data -- reject anything else. Maps to an {@code int[]}.33    */34   ALLOWED_LENGTHS(int[].class),35 36   /**37    * Assume Code 39 codes employ a check digit. Doesn't matter what it maps to;38    * use {@link Boolean#TRUE}.39    */40   ASSUME_CODE_39_CHECK_DIGIT(Void.class),41 42   /**43    * Assume the barcode is being processed as a GS1 barcode, and modify behavior as needed.44    * For example this affects FNC1 handling for Code 128 (aka GS1-128). Doesn't matter what it maps to;45    * use {@link Boolean#TRUE}.46    */47   ASSUME_GS1(Void.class),48 49   /**50    * The caller needs to be notified via callback when a possible {@link ResultPoint}51    * is found. Maps to a {@link ResultPointCallback}.52    */53   NEED_RESULT_POINT_CALLBACK(ResultPointCallback.class),54 55   // End of enumeration values.56   ;57 58   /**59    * Data type the hint is expecting.60    * Among the possible values the {@link Void} stands out as being used for61    * hints that do not expect a value to be supplied (flag hints). Such hints62    * will possibly have their value ignored, or replaced by a63    * {@link Boolean#TRUE}. Hint suppliers should probably use64    * {@link Boolean#TRUE} as directed by the actual hint documentation.65    */66   private final Class<?> valueType;67 68   DecodeHintType(Class<?> valueType) {69     this.valueType = valueType;70   }71   72   public Class<?> getValueType() {73     return valueType;74   }75 76 }

然后我们看下android里面是如何调用的，入口是CaptureActivity,在com.google.zxing.client.android package中，以下描述一个通用的流程

zxing二维码扫描的流程简析（Android版）_第4张图片

CaptureAct中的onResume中的initCamera初始化CaptureActHandler,其构造函数中新起了一个DecodeThread去异步准备一个DecodeHandler，然后调用restartPreviewAndDecode方法，让DecodeHandler去处理R.id.decode的消息，当然这里需要处理一些线程同步问题，代码里用到了CountDownLatch来控制。DecodeHanlder处理R.id.decode消息后用传递R.id.decode_succeeded消息给CaptureActHanlder，最终再调用handleDecode传递给CaptureAct.

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