我正在查看 Android Camera 代码，当我尝试导入时android.os.SystemProperties，找不到它。
我创建了一个新的 2.1 项目并尝试再次导入此命名空间，但仍然找不到。我检查了https://developer.android.com并SystemProperties没有列出。
我错过了什么？
问问题
95526 次
8 回答
65
如果你使用“反射”选项，你可以使用下面的类
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
}
}
}
于 2011-04-05T13:51:46.397 回答
36
这是Android源代码中的类：
{@hide}在 JavaDoc 类中看到了吗？这意味着此类不会作为公共 SDK 的一部分导出。
相机应用程序将其作为内部使用，他们不会使用公共 SDK 来构建它。
你可能仍然可以上这门课
通过反思或
通过获取源代码、删除
@hide并制作您自己的定制 SDK。
但是，根据定义，您现在正在使用“ off SDK”，因此您的应用程序很可能会被破坏或在操作系统版本上出现不同的行为，因为 Android 人员会不遗余力地不在版本之间更改此类。
于 2010-04-14T21:34:02.943 回答
27
作为用户 Void 的答案发布的课程有很多不必要的东西。这是我在android.os.SystemProperties上使用反射的类：
/*
* 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");
}
}
于 2015-02-09T03:31:56.480 回答
16
您可以执行以下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();
于 2010-09-22T18:12:35.857 回答
15
经过一番折腾，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：
您需要成为系统用户，在清单中添加：android:sharedUserId="android.uid.system"。
您需要使用平台密钥签署您的 APK，我作弊并覆盖了 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
本机系统属性服务有一个 ACL，它控制对您可以破坏密钥空间（例如 sys. 或 debug.）的属性的所有写访问。请参阅 /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，如果您正在滚动自己的构建，如果您真的想要，您可以添加自己的密钥，但重用上述之一似乎更容易。
于 2012-06-20T16:06:22.833 回答
4
以下是您可以从系统属性中读取的方法。我也包括了一个后备：
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
}
}
使用反射比从进程输出中读取要快得多。在我测试过的某些设备（小米红米 8）上大约快 x30。
所以值得一试。
于 2020-08-02T14:41:53.267 回答
2
经过大量搜索，我找到了一种为 Android 设置系统属性的方法。我无法找到适用于 Android Lollipop 版本的解决方案。但我成功地做到了这一点。为了设置系统属性，我们需要使用：
import android.os.SystemProperties
SystemProperties.set(key, value).
例如SystemProperties.set("sys.android", 5.0)
现在您需要为新的系统属性授予权限转到/home/inkkashy04/Android_Lollypop/external/sepolicy/property_contexts
并为您的属性授予适当的权限
sys.android u:object_r:system_prop:s0
现在，在刷新映像后，您可以看到命令列出的系统属性：
adb shell getprop
于 2015-06-17T07:36:56.850 回答
0
梯度方法：
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")
}
于 2019-03-28T09:34:51.297 回答