获取APK文件的签名信息，反射实现

private String showUninstallAPKSignatures(String apkPath) {
         String PATH_PackageParser = "android.content.pm.PackageParser";
         try {
             // apk包的文件路径
             // 这是一个Package 解释器, 是隐藏的
             // 构造函数的参数只有一个, apk文件的路径
             // PackageParser packageParser = new PackageParser(apkPath);
             Class pkgParserCls = Class.forName(PATH_PackageParser);
             Class[] typeArgs = new Class[1];
             typeArgs[0] = String.class;
             Constructor pkgParserCt = pkgParserCls.getConstructor(typeArgs);
             Object[] valueArgs = new Object[1];
             valueArgs[0] = apkPath;
             Object pkgParser = pkgParserCt.newInstance(valueArgs);
             MediaApplication.logD(DownloadApk.class, "pkgParser:" + pkgParser.toString());
             // 这个是与显示有关的, 里面涉及到一些像素显示等等, 我们使用默认的情况
             DisplayMetrics metrics = new DisplayMetrics();
             metrics.setToDefaults();
             // PackageParser.Package mPkgInfo = packageParser.parsePackage(new
             // File(apkPath), apkPath,
             // metrics, 0);
             typeArgs = new Class[4];
             typeArgs[0] = File.class;
             typeArgs[1] = String.class;
             typeArgs[2] = DisplayMetrics.class;
             typeArgs[3] = Integer.TYPE;
             Method pkgParser_parsePackageMtd = pkgParserCls.getDeclaredMethod("parsePackage",
                     typeArgs);
             valueArgs = new Object[4];
             valueArgs[0] = new File(apkPath);
             valueArgs[1] = apkPath;
             valueArgs[2] = metrics;
             valueArgs[3] = PackageManager.GET_SIGNATURES;
             Object pkgParserPkg = pkgParser_parsePackageMtd.invoke(pkgParser, valueArgs);
            
             typeArgs = new Class[2];
             typeArgs[0] = pkgParserPkg.getClass();
             typeArgs[1] = Integer.TYPE;
             Method pkgParser_collectCertificatesMtd = pkgParserCls.getDeclaredMethod("collectCertificates",
                     typeArgs);
             valueArgs = new Object[2];
             valueArgs[0] = pkgParserPkg;
             valueArgs[1] = PackageManager.GET_SIGNATURES;
             pkgParser_collectCertificatesMtd.invoke(pkgParser, valueArgs);
             // 应用程序信息包, 这个公开的, 不过有些函数, 变量没公开
             Field packageInfoFld = pkgParserPkg.getClass().getDeclaredField("mSignatures");
             Signature[] info = (Signature[]) packageInfoFld.get(pkgParserPkg);
             MediaApplication.logD(DownloadApk.class, "size:"+info.length);
             MediaApplication.logD(DownloadApk.class, info[0].toCharsString());
             return info[0].toCharsString();
         } catch (Exception e) {
             e.printStackTrace();
         }
         return null;
     } 获取程序自身的签名：private String getSign(Context context) {
        PackageManager pm = context.getPackageManager();
        List<PackageInfo> apps = pm.getInstalledPackages(PackageManager.GET_SIGNATURES);
        Iterator<PackageInfo> iter = apps.iterator();
        while(iter.hasNext()) {
             PackageInfo packageinfo = iter.next();
             String packageName = packageinfo.packageName;
             if (packageName.equals(instance.getPackageName())) {
                MediaApplication.logD(DownloadApk.class, packageinfo.signatures[0].toCharsString());
                return packageinfo.signatures[0].toCharsString();
             }
     }
        return null;
    } 对比2个方法的返回值来判断APK升级包的签名是否一致，一致就提示可以安装。