Android : 判断平台是否支持wifi功能

一、配置

Android4.0及以上版本的模块判断函数：getPackageManager().hasSystemFeature(String string). 通过该函数判断系统是否有特定的模块功能。
例如判断是否有wifi的具体代码：getPackageManager().hasSystemFeature(PackageManager.FEATURE_WIFI);

PackageManager.FEATURE_WIFI 在PackageManager.java中的定义为：public static final String FEATURE_WIFI = "android.hardware.wifi";

而"android.hardware.wifi"字符串存在系统/system/etc/permissions/xxxx.xml文件里，它们一般从源码/framework/base/data/etc/xxx.xml复制过来（Android7.1 RK平台发现存在于frameworks/native/data/etc/xxx.xml文件）；

二、解析

代码路径：frameworksasecorejavacomandroidserverSystemConfig.java

    void readPermissions(File libraryDir, int permissionFlag) {
        // Read permissions from given directory.
        if (!libraryDir.exists() || !libraryDir.isDirectory()) {
            if (permissionFlag == ALLOW_ALL) {
                Slog.w(TAG, "No directory " + libraryDir + ", skipping");
            }
            return;
        }
        if (!libraryDir.canRead()) {
            Slog.w(TAG, "Directory " + libraryDir + " cannot be read");
            return;
        }

        // Iterate over the files in the directory and scan .xml files
        File platformFile = null;
        for (File f : libraryDir.listFiles()) {
            // We'll read platform.xml last
            if (f.getPath().endsWith("etc/permissions/platform.xml")) {
                platformFile = f;
                continue;
            }

            if (!f.getPath().endsWith(".xml")) {
                Slog.i(TAG, "Non-xml file " + f + " in " + libraryDir + " directory, ignoring");
                continue;
            }
            if (!f.canRead()) {
                Slog.w(TAG, "Permissions library file " + f + " cannot be read");
                continue;
            }

            readPermissionsFromXml(f, permissionFlag); //解析etc/permissions/下所有的.xml文件并提取支持的feature

        }

        // Read platform permissions last so it will take precedence
        if (platformFile != null) {
            readPermissionsFromXml(platformFile, permissionFlag);
        }
    }