android.os.SystemProperties在哪里？

Question

我正在查看Android相机代码，当我尝试导入android.os.SystemProperties时，无法找到它。

这是我正在查看的文件：
https://android.googlesource.com/platform/packages/apps/Camera/+/eclair-release/src/com/android/camera/VideoCamera.java

我创建了一个新的2.1项目并尝试再次导入此命名空间，但仍无法找到它。我检查了https://developer.android.com，但未列出SystemProperties。

我错过了什么吗？

Answer 1

如果您使用“反射”选项，则可以使用下面的课程

package com.etc.etc;

import java.io.File;
import java.lang.reflect.Method;
import android.content.Context;
import dalvik.system.DexFile;


public class SystemPropertiesProxy
{

/**
 * This class cannot be instantiated
 */
private SystemPropertiesProxy(){

}

    /**
     * Get the value for the given key.
     * @return an empty string if the key isn't found
     * @throws IllegalArgumentException if the key exceeds 32 characters
     */
    public static String get(Context context, String key) throws IllegalArgumentException {

        String ret= "";

        try{

          ClassLoader cl = context.getClassLoader(); 
          @SuppressWarnings("rawtypes")
          Class SystemProperties = cl.loadClass("android.os.SystemProperties");

          //Parameters Types
          @SuppressWarnings("rawtypes")
              Class[] paramTypes= new Class[1];
          paramTypes[0]= String.class;

          Method get = SystemProperties.getMethod("get", paramTypes);

          //Parameters
          Object[] params= new Object[1];
          params[0]= new String(key);

          ret= (String) get.invoke(SystemProperties, params);

        }catch( IllegalArgumentException iAE ){
            throw iAE;
        }catch( Exception e ){
            ret= "";
            //TODO
        }

        return ret;

    }

    /**
     * Get the value for the given key.
     * @return if the key isn't found, return def if it isn't null, or an empty string otherwise
     * @throws IllegalArgumentException if the key exceeds 32 characters
     */
    public static String get(Context context, String key, String def) throws IllegalArgumentException {

        String ret= def;

        try{

          ClassLoader cl = context.getClassLoader(); 
          @SuppressWarnings("rawtypes")
          Class SystemProperties = cl.loadClass("android.os.SystemProperties");

          //Parameters Types
          @SuppressWarnings("rawtypes")
              Class[] paramTypes= new Class[2];
          paramTypes[0]= String.class;
          paramTypes[1]= String.class;          

          Method get = SystemProperties.getMethod("get", paramTypes);

          //Parameters
          Object[] params= new Object[2];
          params[0]= new String(key);
          params[1]= new String(def);

          ret= (String) get.invoke(SystemProperties, params);

        }catch( IllegalArgumentException iAE ){
            throw iAE;
        }catch( Exception e ){
            ret= def;
            //TODO
        }

        return ret;

    }

    /**
     * Get the value for the given key, and return as an integer.
     * @param key the key to lookup
     * @param def a default value to return
     * @return the key parsed as an integer, or def if the key isn't found or
     *         cannot be parsed
     * @throws IllegalArgumentException if the key exceeds 32 characters
     */
    public static Integer getInt(Context context, String key, int def) throws IllegalArgumentException {

        Integer ret= def;

        try{

          ClassLoader cl = context.getClassLoader(); 
          @SuppressWarnings("rawtypes")
          Class SystemProperties = cl.loadClass("android.os.SystemProperties");

          //Parameters Types
          @SuppressWarnings("rawtypes")
              Class[] paramTypes= new Class[2];
          paramTypes[0]= String.class;
          paramTypes[1]= int.class;  

          Method getInt = SystemProperties.getMethod("getInt", paramTypes);

          //Parameters
          Object[] params= new Object[2];
          params[0]= new String(key);
          params[1]= new Integer(def);

          ret= (Integer) getInt.invoke(SystemProperties, params);

        }catch( IllegalArgumentException iAE ){
            throw iAE;
        }catch( Exception e ){
            ret= def;
            //TODO
        }

        return ret;

    }

    /**
     * Get the value for the given key, and return as a long.
     * @param key the key to lookup
     * @param def a default value to return
     * @return the key parsed as a long, or def if the key isn't found or
     *         cannot be parsed
     * @throws IllegalArgumentException if the key exceeds 32 characters
     */
    public static Long getLong(Context context, String key, long def) throws IllegalArgumentException {

        Long ret= def;

        try{

          ClassLoader cl = context.getClassLoader();
          @SuppressWarnings("rawtypes")
              Class SystemProperties= cl.loadClass("android.os.SystemProperties");

          //Parameters Types
          @SuppressWarnings("rawtypes")
              Class[] paramTypes= new Class[2];
          paramTypes[0]= String.class;
          paramTypes[1]= long.class;  

          Method getLong = SystemProperties.getMethod("getLong", paramTypes);

          //Parameters
          Object[] params= new Object[2];
          params[0]= new String(key);
          params[1]= new Long(def);

          ret= (Long) getLong.invoke(SystemProperties, params);

        }catch( IllegalArgumentException iAE ){
            throw iAE;
        }catch( Exception e ){
            ret= def;
            //TODO
        }

        return ret;

    }

    /**
     * Get the value for the given key, returned as a boolean.
     * Values 'n', 'no', '0', 'false' or 'off' are considered false.
     * Values 'y', 'yes', '1', 'true' or 'on' are considered true.
     * (case insensitive).
     * If the key does not exist, or has any other value, then the default
     * result is returned.
     * @param key the key to lookup
     * @param def a default value to return
     * @return the key parsed as a boolean, or def if the key isn't found or is
     *         not able to be parsed as a boolean.
     * @throws IllegalArgumentException if the key exceeds 32 characters
     */
    public static Boolean getBoolean(Context context, String key, boolean def) throws IllegalArgumentException {

        Boolean ret= def;

        try{

          ClassLoader cl = context.getClassLoader(); 
          @SuppressWarnings("rawtypes")
          Class SystemProperties = cl.loadClass("android.os.SystemProperties");

          //Parameters Types
          @SuppressWarnings("rawtypes")
              Class[] paramTypes= new Class[2];
          paramTypes[0]= String.class;
          paramTypes[1]= boolean.class;  

          Method getBoolean = SystemProperties.getMethod("getBoolean", paramTypes);

          //Parameters         
          Object[] params= new Object[2];
          params[0]= new String(key);
          params[1]= new Boolean(def);

          ret= (Boolean) getBoolean.invoke(SystemProperties, params);

        }catch( IllegalArgumentException iAE ){
            throw iAE;
        }catch( Exception e ){
            ret= def;
            //TODO
        }

        return ret;

    }

    /**
     * Set the value for the given key.
     * @throws IllegalArgumentException if the key exceeds 32 characters
     * @throws IllegalArgumentException if the value exceeds 92 characters
     */
    public static void set(Context context, String key, String val) throws IllegalArgumentException {

        try{

          @SuppressWarnings("unused")
          DexFile df = new DexFile(new File("/system/app/Settings.apk"));
          @SuppressWarnings("unused")
          ClassLoader cl = context.getClassLoader(); 
          @SuppressWarnings("rawtypes")
          Class SystemProperties = Class.forName("android.os.SystemProperties");

          //Parameters Types
          @SuppressWarnings("rawtypes")
              Class[] paramTypes= new Class[2];
          paramTypes[0]= String.class;
          paramTypes[1]= String.class;  

          Method set = SystemProperties.getMethod("set", paramTypes);

          //Parameters         
          Object[] params= new Object[2];
          params[0]= new String(key);
          params[1]= new String(val);

          set.invoke(SystemProperties, params);

        }catch( IllegalArgumentException iAE ){
            throw iAE;
        }catch( Exception e ){
            //TODO
        }

    }
}

Answer 2

这是Android源代码中的类：

https://android.googlesource.com/platform/frameworks/base/+/eclair-release/core/java/android/os/SystemProperties.java

请参阅JavaDoc类中的{@hide}？这意味着此类不会作为公共SDK的一部分导出。

相机应用程序使用它作为内部，他们不会使用公共SDK来构建它。

你仍然可以参加这个课程

1. 通过反思或

2. 获取来源，删除@hide并制作自己的 自定义SDK。

然而，根据定义，你现在正在“off SDK”，因此你的应用程序可能会被破坏或在操作系统版本上获得不同的行为，因为Android人员将不费力地不在版本之间更改此类。

Answer 3

作为用户Void的答案发布的课程有一堆不必要的东西。这是我在android.os.SystemProperties使用反射的课程：

/*
 * Copyright (C) 2015 Jared Rummler
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * Gives access to the system properties store. The system properties store contains a list of
 * string key-value pairs.
 */
public class SystemProperties {

  private static final Class<?> SP = getSystemPropertiesClass();

  /**
   * Get the value for the given key.
   */
  public static String get(String key) {
    try {
      return (String) SP.getMethod("get", String.class).invoke(null, key);
    } catch (Exception e) {
      return null;
    }
  }

  /**
   * Get the value for the given key.
   *
   * @return if the key isn't found, return def if it isn't null, or an empty string otherwise
   */
  public static String get(String key, String def) {
    try {
      return (String) SP.getMethod("get", String.class, String.class).invoke(null, key, def);
    } catch (Exception e) {
      return def;
    }
  }

  /**
   * Get the value for the given key, returned as a boolean. Values 'n', 'no', '0', 'false' or
   * 'off' are considered false. Values 'y', 'yes', '1', 'true' or 'on' are considered true. (case
   * sensitive). If the key does not exist, or has any other value, then the default result is
   * returned.
   *
   * @param key
   *     the key to lookup
   * @param def
   *     a default value to return
   * @return the key parsed as a boolean, or def if the key isn't found or is not able to be
   * parsed as a boolean.
   */
  public static boolean getBoolean(String key, boolean def) {
    try {
      return (Boolean) SP.getMethod("getBoolean", String.class, boolean.class)
          .invoke(null, key, def);
    } catch (Exception e) {
      return def;
    }
  }

  /**
   * Get the value for the given key, and return as an integer.
   *
   * @param key
   *     the key to lookup
   * @param def
   *     a default value to return
   * @return the key parsed as an integer, or def if the key isn't found or cannot be parsed
   */
  public static int getInt(String key, int def) {
    try {
      return (Integer) SP.getMethod("getInt", String.class, int.class).invoke(null, key, def);
    } catch (Exception e) {
      return def;
    }
  }

  /**
   * Get the value for the given key, and return as a long.
   *
   * @param key
   *     the key to lookup
   * @param def
   *     a default value to return
   * @return the key parsed as a long, or def if the key isn't found or cannot be parsed
   */
  public static long getLong(String key, long def) {
    try {
      return (Long) SP.getMethod("getLong", String.class, long.class).invoke(null, key, def);
    } catch (Exception e) {
      return def;
    }
  }

  private static Class<?> getSystemPropertiesClass() {
    try {
      return Class.forName("android.os.SystemProperties");
    } catch (ClassNotFoundException shouldNotHappen) {
      return null;
    }
  }

  private SystemProperties() {
    throw new AssertionError("no instances");
  }

}

Answer 4

经过大量的讨论后，我终于得到了上面的反射代码来设置和创建新的本机系统属性，有一些警告：

1. 您需要成为系统用户，将：android：sharedUserId =“android.uid.system”添加到清单。

2. 您需要使用平台密钥签署您的APK，我作弊并且只是覆盖了eclipse中的默认调试签名密钥，如下所示： http://stoned-android.blogspot.co.uk/2012_01_01_archive.html

3. 本机系统属性服务具有一个ACL，用于控制对可以破坏密钥空间（例如sys。或debug。）的属性的所有写访问权限。看到 /system/core/init/property_service.c：

   {“net。”，AID_SYSTEM，0}， {“dev。”，AID_SYSTEM，0}， {“runtime。”，AID_SYSTEM，0}， {“hw。”，AID_SYSTEM，0}， {“sys。”，AID_SYSTEM，0}， {“service。”，AID_SYSTEM，0}， {“wlan。”，AID_SYSTEM，0}， {“dhcp。”，AID_SYSTEM，0}，

或者，如果你正在推动自己的构建，你可以添加你自己的密钥，如果你真的想要，但似乎更容易重用上面的一个。

Answer 5

您可以执行getprop命令：

String line = "";
try {
 Process ifc = Runtime.getRuntime().exec("getprop ro.hardware");
 BufferedReader bis = new BufferedReader(new InputStreamReader(ifc.getInputStream()));
 line = bis.readLine();
} catch (java.io.IOException e) {
}
ifc.destroy();

Answer 6

经过大量搜索后，我找到了一种为Android设置系统属性的方法。 我无法找到Android Lollipop版本的解决方案。但我成功地这样做了。要设置系统属性，我们需要使用：

import android.os.SystemProperties
SystemProperties.set(key, value).

e.g。 SystemProperties.set("sys.android", 5.0)

现在您需要授予新系统属性的权限 转到/home/inkkashy04/Android_Lollypop/external/sepolicy/property_contexts 并给予您的财产适当的许可

  

sys.android u：object_r：system_prop：s0

现在，在闪烁图像后，您可以通过命令查看系统属性：

adb shell getprop

Answer 7

这是从系统属性中读取内容的方法。我也提供了一个备用广告：

import android.annotation.SuppressLint
import java.io.*
import java.lang.reflect.Method

object SystemProperties {
    private var failedUsingReflection = false
    private var getPropMethod: Method? = null

    @SuppressLint("PrivateApi")
    fun getProp(propName: String, defaultResult: String = ""): String {
        if (!failedUsingReflection) try {
            if (getPropMethod == null) {
                val clazz = Class.forName("android.os.SystemProperties")
                getPropMethod = clazz.getMethod("get", String::class.java, String::class.java)
            }
            return getPropMethod!!.invoke(null, propName, defaultResult) as String? ?: defaultResult
        } catch (e: Exception) {
            getPropMethod = null
            failedUsingReflection = true
        }
        var process: Process? = null
        try {
            process = Runtime.getRuntime().exec("getprop \"$propName\" \"$defaultResult\"")
            val reader = BufferedReader(InputStreamReader(process.inputStream))
            return reader.readLine()
        } catch (e: IOException) {
        } finally {
            process?.destroy()
        }
        return defaultResult
    }
}

使用反射，它的工作原理比从过程输出中读取要快得多。在我测试过的某些设备（小米Redmi 8）上，速度提高了大约30倍。

因此值得尝试。

Answer 8

分级方法：

String SDK_DIR = System.getenv("ANDROID_SDK_HOME")
if(SDK_DIR == null) {
    Properties props = new Properties()
    props.load(new FileInputStream(project.rootProject.file("local.properties")))
    SDK_DIR = props.get('sdk.dir');
}
dependencies {
    compileOnly files("${SDK_DIR}/platforms/android-25/data/layoutlib.jar")
}