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。
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
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
public final class MultiFormatWriter implements Writer {
@Override
public BitMatrix encode(String contents,
BarcodeFormat format,
int width,
int height) throws WriterException {
return encode(contents, format, width, height, null);
}
@Override
public BitMatrix encode(String contents,
BarcodeFormat format,
int width, int height,
Map<EncodeHintType,?> hints) throws WriterException {
Writer writer;
switch (format) {
case EAN_8:
writer = new EAN8Writer();
break;
case EAN_13:
writer = new EAN13Writer();
break;
case UPC_A:
writer = new UPCAWriter();
break;
case QR_CODE:
writer = new QRCodeWriter();
break;
case CODE_39:
writer = new Code39Writer();
break;
case CODE_128:
writer = new Code128Writer();
break;
case ITF:
writer = new ITFWriter();
break;
case PDF_417:
writer = new PDF417Writer();
break;
case CODABAR:
writer = new CodaBarWriter();
break;
case DATA_MATRIX:
writer = new DataMatrixWriter();
break;
case AZTEC:
writer = new AztecWriter();
break;
default:
throw new IllegalArgumentException("No encoder available for format " + format);
}
return writer.encode(contents, format, width, height, hints);
}
}
然后看解析二维码的类结构
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
public final class MultiFormatReader implements Reader {
private Map<DecodeHintType,?> hints;
private Reader[] readers;
@Override
public Result decode(BinaryBitmap image) throws NotFoundException {
setHints(null);
return decodeInternal(image);
}
@Override
public Result decode(BinaryBitmap image, Map<DecodeHintType,?> hints) throws NotFoundException {
setHints(hints);
return decodeInternal(image);
}
public Result decodeWithState(BinaryBitmap image) throws NotFoundException {
// Make sure to set up the default state so we don't crash
if (readers == null) {
setHints(null);
}
return decodeInternal(image);
}
public void setHints(Map<DecodeHintType,?> hints) {//根据设置的hint来设置reader
this.hints = hints;
boolean tryHarder = hints != null && hints.containsKey(DecodeHintType.TRY_HARDER);
@SuppressWarnings("unchecked")
Collection<BarcodeFormat> formats =
hints == null ? null : (Collection<BarcodeFormat>) hints.get(DecodeHintType.POSSIBLE_FORMATS);
Collection<Reader> readers = new ArrayList<Reader>();
if (formats != null) {
boolean addOneDReader =
formats.contains(BarcodeFormat.UPC_A) ||
formats.contains(BarcodeFormat.UPC_E) ||
formats.contains(BarcodeFormat.EAN_13) ||
formats.contains(BarcodeFormat.EAN_8) ||
formats.contains(BarcodeFormat.CODABAR) ||
formats.contains(BarcodeFormat.CODE_39) ||
formats.contains(BarcodeFormat.CODE_93) ||
formats.contains(BarcodeFormat.CODE_128) ||
formats.contains(BarcodeFormat.ITF) ||
formats.contains(BarcodeFormat.RSS_14) ||
formats.contains(BarcodeFormat.RSS_EXPANDED);
// Put 1D readers upfront in "normal" mode
if (addOneDReader && !tryHarder) {
readers.add(new MultiFormatOneDReader(hints));
}
if (formats.contains(BarcodeFormat.QR_CODE)) {
readers.add(new QRCodeReader());
}
if (formats.contains(BarcodeFormat.DATA_MATRIX)) {
readers.add(new DataMatrixReader());
}
if (formats.contains(BarcodeFormat.AZTEC)) {
readers.add(new AztecReader());
}
if (formats.contains(BarcodeFormat.PDF_417)) {
readers.add(new PDF417Reader());
}
if (formats.contains(BarcodeFormat.MAXICODE)) {
readers.add(new MaxiCodeReader());
}
// At end in "try harder" mode
if (addOneDReader && tryHarder) {
readers.add(new MultiFormatOneDReader(hints));
}
}
if (readers.isEmpty()) {
if (!tryHarder) {
readers.add(new MultiFormatOneDReader(hints));
}
readers.add(new QRCodeReader());
readers.add(new DataMatrixReader());
readers.add(new AztecReader());
readers.add(new PDF417Reader());
readers.add(new MaxiCodeReader());
if (tryHarder) {
readers.add(new MultiFormatOneDReader(hints));
}
}
this.readers = readers.toArray(new Reader[readers.size()]);
}
@Override
public void reset() {
if (readers != null) {
for (Reader reader : readers) {
reader.reset();
}
}
}
private Result decodeInternal(BinaryBitmap image) throws NotFoundException {//最终都调用这个方法
if (readers != null) {
for (Reader reader : readers) {
try {
return reader.decode(image, hints);
} catch (ReaderException re) {
// continue
}
}
}
throw NotFoundException.getNotFoundInstance();
}
}
DecodeHintType的语法比较有意思，还在理解中
public enum DecodeHintType {
/**
* Unspecified, application-specific hint. Maps to an unspecified {@link Object}.
*/
OTHER(Object.class),
/**
* Image is a pure monochrome image of a barcode. Doesn't matter what it maps to;
* use {@link Boolean#TRUE}.
*/
PURE_BARCODE(Void.class),
/**
* Image is known to be of one of a few possible formats.
* Maps to a {@link List} of {@link BarcodeFormat}s.
*/
POSSIBLE_FORMATS(List.class),
/**
* Spend more time to try to find a barcode; optimize for accuracy, not speed.
* Doesn't matter what it maps to; use {@link Boolean#TRUE}.
*/
TRY_HARDER(Void.class),
/**
* Specifies what character encoding to use when decoding, where applicable (type String)
*/
CHARACTER_SET(String.class),
/**
* Allowed lengths of encoded data -- reject anything else. Maps to an {@code int[]}.
*/
ALLOWED_LENGTHS(int[].class),
/**
* Assume Code 39 codes employ a check digit. Doesn't matter what it maps to;
* use {@link Boolean#TRUE}.
*/
ASSUME_CODE_39_CHECK_DIGIT(Void.class),
/**
* Assume the barcode is being processed as a GS1 barcode, and modify behavior as needed.
* For example this affects FNC1 handling for Code 128 (aka GS1-128). Doesn't matter what it maps to;
* use {@link Boolean#TRUE}.
*/
ASSUME_GS1(Void.class),
/**
* The caller needs to be notified via callback when a possible {@link ResultPoint}
* is found. Maps to a {@link ResultPointCallback}.
*/
NEED_RESULT_POINT_CALLBACK(ResultPointCallback.class),
// End of enumeration values.
;
/**
* Data type the hint is expecting.
* Among the possible values the {@link Void} stands out as being used for
* hints that do not expect a value to be supplied (flag hints). Such hints
* will possibly have their value ignored, or replaced by a
* {@link Boolean#TRUE}. Hint suppliers should probably use
* {@link Boolean#TRUE} as directed by the actual hint documentation.
*/
private final Class<?> valueType;
DecodeHintType(Class<?> valueType) {
this.valueType = valueType;
}
public Class<?> getValueType() {
return valueType;
}
}
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
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.