cts 检查系统有哪些功能

问题

cts测试时发现在result.xml头部中有很多关于手机的信息，包括当前系统有哪些功能，以及build版本等等，这些心怎么显示出来的？

分析

cts 测试中会在TestDeviceSetup app中调用 getFeatures() 该方法返回所有系统的feature，该app是cts的tool源码路径为/cts/tool/device-setup.

getFeature的具体实现：

StringBuilder features = new StringBuilder();

try {

Set<String> checkedFeatures = new HashSet<String>();

PackageManager packageManager = getContext().getPackageManager();

for (String featureName : getPackageManagerFeatures())
{

checkedFeatures.add(featureName);

boolean hasFeature = packageManager.hasSystemFeature(featureName);

addFeature(features, featureName, "sdk", hasFeature);

}

FeatureInfo[] featureInfos = packageManager.getSystemAvailableFeatures();

if (featureInfos != null) {

for (FeatureInfo featureInfo : featureInfos) {

if (featureInfo.name != null && !checkedFeatures.contains(featureInfo.name)) {

addFeature(features, featureInfo.name, "other", true);

}

}

}

} catch (Exception exception) {

Log.e(TAG, "Error getting features: " + exception.getMessage(), exception);

}

实现上分为两步：

1）直接从PackageManager类中获取，该类定义了系统的大部分feature的字符串常量；

private List<String> getPackageManagerFeatures() {

try {

List<String> features = new ArrayList<String>();

Field[] fields = PackageManager.class.getFields();

for (Field field : fields) {

if (field.getName().startsWith("FEATURE_")) {

String feature = (String) field.get(null);

features.add(feature);

}

}

return features;

} catch (IllegalAccessException illegalAccess) {

throw new RuntimeException(illegalAccess);

}

}

该方法是用发射机制将PackageManager类中的以FEATURE_公共常量列出来。下面是该类中的部分常量；

@SdkConstant(SdkConstantType.FEATURE)

public static final String FEATURE_AUDIO_LOW_LATENCY = "android.hardware.audio.low_latency";

/**

* Feature for {@link #getSystemAvailableFeatures} and

* {@link #hasSystemFeature}: The device is capable of communicating with

* other devices via Bluetooth.

*/

@SdkConstant(SdkConstantType.FEATURE)

public static final String FEATURE_BLUETOOTH = "android.hardware.bluetooth";

/**

* Feature for {@link #getSystemAvailableFeatures} and

* {@link #hasSystemFeature}: The device has a camera facing away

* from the screen.

*/

@SdkConstant(SdkConstantType.FEATURE)

public static final String FEATURE_CAMERA = "android.hardware.camera";

/**

* Feature for {@link #getSystemAvailableFeatures} and

* {@link #hasSystemFeature}: The device's camera supports auto-focus.

*/

@SdkConstant(SdkConstantType.FEATURE)

public static final String FEATURE_CAMERA_AUTOFOCUS = "android.hardware.camera.autofocus";

/*

2）系统在启动PackageMangerService时会将对应的系统Feature加载并保存 在一个HashMap中，那通过在这个容器里找到相关feature的信息，如果有证明存在。

packageManager.getSystemAvailableFeatures(),会返回FeatureInfo的数组，保存的是一些Feature的信息。

该数组的获取就是通过前面提到的HashMap 对象有关。

系统启动的时候怎么判断是否有哪些Feature，就是通过解析获取/sys/etc下的xml来的。

该文件有很多的系统Feature的定义