Android常用API

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Android三种方式设置和获取属性：
1. Native层使用property_get和property_set，头文件cutils/properties.h和libcutil库。
2. Java层使用System.getProperty和System.setProperty方法。该系统属性与native层系统属性存储空间不同。
3. Java层android.os.SystemProperties可以操作Android系统属性，该类通过JNI调用Native的property_get和property_set方法来获得和设置属性。
4. Shell脚本可以使用setprop和getprop命令来设置和获取属性。

/* property_get: returns the length of the value which will never be** greater than PROPERTY_VALUE_MAX - 1 and will always be zero terminated.** (the length does not include the terminating zero).**** If the property read fails or returns an empty value, the default** value is used (if nonnull).*/int property_get(const char *key, char *value, const char *default_value);/* property_set: returns 0 on success, < 0 on failure */int property_set(const char *key, const char *value);

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Android组件和线程是不同的概念，体现MVC

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frameworks/base/core/java/android/os/UEventObserver.java用来监听UEVENT。 例如

device/xxx/frameworks/services/java/com/xxx/server/xxxHDMIRxService.java初始化时mHDMIRxObserver.startObserving(HdmiRxUeventKeyword)，然后

private UEventObserver mHDMIRxObserver = new UEventObserver() {@Overridepublic void onUEvent(UEventObserver.UEvent event) {            Slog.w(TAG, "mHDMIRxObserver:onUEvent");    setHdmiRxPlugged("1".equals(event.get("SWITCH_STATE")));}};

device/xxx/frameworks/core/java/com/xxx/hardware/xxxHDMIManager.java中获取service

mRtkHDMIService = IRtkHDMIService.Stub.asInterface(ServiceManager.getService("RtkHDMIService"));

通过AIDL IxxxHDMIRxService.aidl调用service功能。

driver/media/platform/xxx_hdmirx/v4l2_hdmi_dev.c/update_hdmirx_switch_state()

driver/switch/switch_class.c/switch_set_state()/kobject_uevent_env()

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Android启动hotspot的java代码可以配置的内容很少，如果需要高级配置功能需要到底层去控制。

使用netd启动hostapd的文件：android/system/netd/server/SoftapController.cpp，相关类：

WifiManagerWifiConfiguration...

位置：

android/frameworks/base/wifi/java/android/net/wifi/*

android/frameworks/opt/net/wifi/service/java/com/android/server/wifi/*
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JNI Sample

1. CPP

#include <JNIHelp.h>#define CLASS_NAME_UTILS            "com/example/Utils"#define CREATE_CRASH 0
static JavaVM *g_VM;
static jstring native_getWifiMac(JNIEnv * env, jobject obj, jstring ifname){const char *ifn = env->GetStringUTFChars(ifname, 0);char cap[128];ALOGE("jni, Call native_getWifiMac!\n");strcpy(cap, ifn);env->ReleaseStringUTFChars(ifname, ifn);FILE *fp = fopen("/sys/class/net/wlan0/address", "r");if(fp) {ALOGE("HDMIRxDemo: jni %d\n", __LINE__);fscanf(fp, "%s", cap);fclose(fp);} else {ALOGE("HDMIRxDemo: jni %d\n", __LINE__);}return env->NewStringUTF(cap);}static void native_prepare(JNIEnv * /*env*/ , jobject /*obj*/){ ALOGV("call [%s]",__FUNCTION__);}static void native_init(JNIEnv * /*env*/ , jobject /*obj*/){ ALOGV("call [%s]",__FUNCTION__);}static void abc(JNIEnv * /*env*/, jobject /*obj*/, jint bc, jlong startTime, jlong endTime)
{
    ALOGV("call [%s]",__FUNCTION__);
}static JNINativeMethod gUtilsMethods[] = { {"init","()V",(void*)native_init}, {"prepare","()V",(void*)native_prepare},
    {"abc","(IJJ)V",(void*)abc},
 {"getWifiMac","(Ljava/lang/String;)Ljava/lang/String;",(void*)native_getWifiMac},};static int register_jni(JNIEnv *env){ ALOGE("jni, Call register_jni!\n"); return jniRegisterNativeMethods(env,CLASS_NAME_UTILS,gUtilsMethods,NELEM(gUtilsMethods));}extern "C" JNIEXPORT void JNI_OnUnload(JavaVM* /*vm*/, void* /*reserved*/){ ALOGE("Call JNI_OnUnload!\n");}extern "C" JNIEXPORT jint JNI_OnLoad(JavaVM* vm, void* /*reserved*/){ JNIEnv* env = NULL; jint result = -1; g_VM=vm; ALOGE("jni, Call JNI_Onload!\n"); if (vm->GetEnv((void**) &env, JNI_VERSION_1_4) != JNI_OK) { ALOGE("GetEnv failed!\n"); return result; } if(register_jni(env)<0) return -1; return JNI_VERSION_1_4;}
2. Java
package com.example;public class Utils {    private static Utils sInstance = null;    static {        System.loadLibrary("utils");    }    public native void init();    public native void prepare();    public native String getWifiMac(String ifname);    public static Utils getInstance(){        if(sInstance == null){            sInstance = new Utils();        }        return sInstance;    }}// Usagetry {    Log.d(TAG, "getWifiMac");    return Utils.getInstance().getWifiMac(ifname);}catch(Exception e) {        e.printStackTrace();   } 


写文件
String path = null;File file = null;OutputStream os = null;OutputStreamWriter osw = null;BufferedWriter bw = null;StringBuffer sb = null;try {    sb = new StringBuffer();    sb.append("abc\n");    path = context.getFilesDir() + "/abc.conf";     file = new File(path);    if(!file.exists())        file.createNewFile();    Runtime.getRuntime().exec("chmod 777 " + path);    os = new FileOutputStream(file, false);    osw = new OutputStreamWriter(os);    bw = new BufferedWriter(osw);    bw.write(sb.toString());    bw.flush();} catch (FileNotFoundException e) {    e.printStackTrace();} catch (IOException e) {    e.printStackTrace();} finally {    try {        bw.close();    } catch (IOException e) {        e.printStackTrace();    }}



获取网卡MAC，android6之后只能获取eth0和lo，获取WiFi网卡地址失败：
/* Method */try {    Enumeration<NetworkInterface> e = NetworkInterface.getNetworkInterfaces();    NetworkInterface network = null;    StringBuilder buf = new StringBuilder();      byte[] address = null;    byte b;    while (e.hasMoreElements()) {          network = e.nextElement();        if (network != null) {            if (!network.getName().equals(ifname)) {                continue;            }            address = network.getHardwareAddress();             if (address == null || address.length <= 0) {                  return null;              }              buf.append(String.format("%02x:", address[0]));             buf.append(String.format("%02x:", address[1]));             buf.append(String.format("%02x:", address[2]));             buf.append(String.format("%02x:", address[3]));             buf.append(String.format("%02x:", address[4]));             buf.append(String.format("%02x",  address[5]));             return buf.toString();        } else {              System.out.println("error");            }      }  }catch(Exception e) {       e.printStackTrace();   }/* Methord */try {    List<NetworkInterface> all = Collections.list(NetworkInterface.getNetworkInterfaces());    for (NetworkInterface nif : all) {        Log.d(TAG, "Name=" + nif.getName());        if (!nif.getName().equalsIgnoreCase("wlan0"))             continue;        byte[] macBytes = nif.getHardwareAddress();        Log.d(TAG, "macBytes=" + macBytes);        if (macBytes == null)            return "";        StringBuilder res1 = new StringBuilder();        for (byte b : macBytes) {            res1.append(Integer.toHexString(b & 0xFF) + ":");        }        Log.d(TAG, "res1=" + res1.toString());        if (res1.length() > 0) {            res1.deleteCharAt(res1.length() - 1);        }        Log.d(TAG, "res1=" + res1.toString());    }    return "abc";}catch(Exception e) {        e.printStackTrace();   }/* Methord */String path = null;File file = null;FileInputStream fis = null;InputStreamReader isr = null;BufferedReader br = null;String mac = null;try {    path = "/sys/class/net/wlan0/address";    file = new File(path);        if(!file.exists())        Log.d(TAG, "File " + path + " not exists");    fis = new FileInputStream(path);    isr = new InputStreamReader(fis, "UTF-8");      br = new BufferedReader(isr);          mac = br.readLine();    Log.d(TAG, "Read wlan0 addr [" + mac + "]");    return mac;  } catch (Exception e) {      e.printStackTrace();  }
/* Methord */
try {
    String mac = "";
    Process pp = Runtime.getRuntime().exec("cat /sys/class/net/wlan0/address");
    InputStreamReader ir = new InputStreamReader(pp.getInputStream());
    LineNumberReader input = new LineNumberReader(ir);
    mac = input.readLine();
    Log.d(TAG, "Read MWTV3 wlan0 addr [" + mac + "]");
} catch (Exception e) {  
    e.printStackTrace();  
}

/* Methord */
char[] mac = new char[128];try {    FileReader reader = new FileReader("/sys/class/net/wlan0/address");    int readLength = reader.read(mac);    Log.d(TAG, "Read wlan0 addr [" + mac.toString() + "]");    reader.close();} catch (Exception e) {      e.printStackTrace();  }return mac.toString();
/* Methord */
try {
    String mac = "";
    Process p = Runtime.getRuntime().exec("ifconfig wlan0");
    InputStreamReader isr = new InputStreamReader(p.getInputStream());
    LineNumberReader lnr = new LineNumberReader(isr);
    String str = lnr.readLine();
    Log.d(TAG, "MWTV3 ifconfig wlan0 [" + str + "]");
    int i = str.indexOf("HWaddr");
    
    p.getInputStream().close();
    isr.close();
    lnr.close();
    
    mac = str.substring(i + 6);
    mac = mac.trim().toLowerCase();
    
    Log.d(TAG, "MWTV3 wlan0 addr [" + mac + "]");
} catch (Exception e) {  
    e.printStackTrace();
}