获取已安装或未安装的apk签名
某些时候需要获取已安装的apk或者是未安装的apk的签名信息，以下代码片段将会很有用。
1.通过app的packageName获取已安装的apk的签名信息
?
public Signature getPackageSignature(Context context, String packageName){PackageManager pm = context.getPackageManager();List<PackageInfo> apps = pm.getInstalledPackages(PackageManager.GET_SIGNATURES);Iterator<PackageInfo> it = apps.iterator();while(it.hasNext()){PackageInfo info = it.next();if(info.packageName.equals(packageName)){return info.signatures[0];}}return null;}?
2.根据文件路径获取未安装的apk的签名信息
由于android平台本身的一个小bug，使用PackageManager方式获取未安装的apk文件的签名会稍微费事一点。
（android平台的这个小bug有些狗血，是因为PackageManager的的getPackageArchiveInfo中少了如下代码的原因导致）
缺少的代码：
?
if ((flags & GET_SIGNATURES) != 0) packageParser.collectCertificates(pkg, 0);
问题的详细信息可以查看以下链接：
https://code.google.com/p/android/issues/detail?id=9151#c8
https://android-review.googlesource.com/#/c/18769/1/core/java/android/content/pm/PackageManager.java
?
这样一来，获取apk文件的签名方式将会变得稍微啰嗦一点
（1）首先自定义一个getPackageArchiveInfo函数，如下：
@SuppressWarnings("unchecked")public PackageInfo getPackageArchiveInfo(String archiveFilePath, int flags){ // Workaround for https://code.google.com/p/android/issues/detail?id=9151#c8 try{ Class packageParserClass = Class.forName( "android.content.pm.PackageParser"); Class[] innerClasses = packageParserClass.getDeclaredClasses(); Class packageParserPackageClass = null; for (Class innerClass : innerClasses){ if (0 == innerClass.getName().compareTo("android.content.pm.PackageParser$Package")){ packageParserPackageClass = innerClass; break; } } Constructor packageParserConstructor = packageParserClass.getConstructor( String.class); Method parsePackageMethod = packageParserClass.getDeclaredMethod( "parsePackage", File.class, String.class, DisplayMetrics.class, int.class); Method collectCertificatesMethod = packageParserClass.getDeclaredMethod( "collectCertificates", packageParserPackageClass, int.class); Method generatePackageInfoMethod = packageParserClass.getDeclaredMethod( "generatePackageInfo", packageParserPackageClass, int[].class, int.class, long.class, long.class); packageParserConstructor.setAccessible(true); parsePackageMethod.setAccessible(true); collectCertificatesMethod.setAccessible(true); generatePackageInfoMethod.setAccessible(true); Object packageParser = packageParserConstructor.newInstance(archiveFilePath); DisplayMetrics metrics = new DisplayMetrics(); metrics.setToDefaults(); final File sourceFile = new File(archiveFilePath); Object pkg = parsePackageMethod.invoke( packageParser, sourceFile, archiveFilePath, metrics, 0); if (pkg == null){ return null; } if ((flags & android.content.pm.PackageManager.GET_SIGNATURES) != 0){ collectCertificatesMethod.invoke(packageParser, pkg, 0); } return (PackageInfo)generatePackageInfoMethod.invoke(null, pkg, null, flags, 0, 0); } catch (Exception e) { Log.e("Signature Monitor", "android.content.pm.PackageParser reflection failed: " + e.toString()); } return null; }?(2)使用自定义的getPackageArchiveInfo函数获取PackageInfo，从而获取签名信息，如下：
/** * * @param context * @param apkFile 文件的全路径信息（包括apk文件的名称），如果是无效的apk文件，返回值为null * @return */public Signature getApkSignatureByFilePath(Context context, String apkFile){PackageInfo newInfo = getPackageArchiveInfo(apkFile, PackageManager.GET_ACTIVITIES | PackageManager.GET_SIGNATURES);if(newInfo != null){if(newInfo.signatures != null && newInfo.signatures.length >0){return newInfo.signatures[0];}}return null;}??