我正在尝试创建一个应用程序，当我点击扫描按钮时会进行20次扫描，最后得到信号的平均rssi值。
我的代码如下：
MainActivity.java
package com.example.scanner;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.List;
import android.annotation.SuppressLint;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.net.wifi.ScanResult;
import android.net.wifi.WifiInfo;
import android.net.wifi.WifiManager;
import android.os.Bundle;
import android.os.Environment;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.Toast;
public class MainActivity extends ActionBarActivity {
WifiManager wifi;
WifiScanReceiver wifireciever;
WifiInfo info;
Button scan, save;
List<ScanResult> wifilist;
ListView list;
String wifis[];
String name;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fragment_main);
list=(ListView)findViewById(R.id.listView1);
scan=(Button)findViewById(R.id.button1);
save=(Button)findViewById(R.id.button2);
scan.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
wifi=(WifiManager)getSystemService(Context.WIFI_SERVICE);
if (wifi.isWifiEnabled()==false){
wifi.setWifiEnabled(true);
}
wifireciever = new WifiScanReceiver();
registerReceiver(wifireciever, new IntentFilter(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));
wifi.startScan();
}
});
save.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
savedata();
}
});
}
public class scan_data {
String SSID;
String BSSID;
int lvl;
int count = 0;
}
protected void onPause() {
unregisterReceiver(wifireciever);
super.onPause();
}
protected void onResume() {
registerReceiver(wifireciever, new IntentFilter(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));
super.onResume();
}
class WifiScanReceiver extends BroadcastReceiver {
@SuppressLint("UseValueOf")
public void onReceive(Context c, Intent intent) {
wifilist = wifi.getScanResults();
info = wifi.getConnectionInfo();
int k = wifilist.size();
scan_data[] data = new scan_data[k];
for (int i=0;i<20;i++){
wifi.startScan();
wifilist = wifi.getScanResults();
int l = wifilist.size();
if (i==0){
for (int j=0;j<l;k++){
data[j].SSID=wifilist.get(j).SSID;
data[j].BSSID=wifilist.get(j).BSSID;
data[j].lvl=wifilist.get(j).level;
data[j].count++;
}
}
else if (i==19){
for (int j=0;j<l;j++){
if (data[j].BSSID.equals(wifilist.get(j).BSSID)){
data[j].lvl=data[j].lvl+wifilist.get(i).level;
data[j].count++;
}
data[j].lvl=data[j].lvl/data[j].count;
wifis = new String[l];
for(int r = 0; r < l; r++){
wifis[j]=("\n" + data[j].SSID + "\n AP Address : " +data[j].BSSID + "\n Signal Strength : " + data[j].lvl).toString();
}
}
list.setAdapter(new ArrayAdapter<String>(getApplicationContext(),
android.R.layout.simple_list_item_1,wifis));
}
else{
for (int j=0;j<l;k++){
if (data[j].BSSID.equals(wifilist.get(j).BSSID)){
data[j].lvl=data[j].lvl+wifilist.get(i).level;
data[j].count++;
}
}
}
}
}
}
protected void savedata() {
// TODO Auto-generated method stub
try {
File sdcard = Environment.getExternalStorageDirectory();
File directory = new File(sdcard.getAbsolutePath() + "/WIFI_RESULT");
directory.mkdirs();
name = new SimpleDateFormat("yyyy-MM-dd HH mm ss").format(new Date());
File file = new File(directory,name + "wifi_data.txt");
FileOutputStream fou = new FileOutputStream(file);
OutputStreamWriter osw = new OutputStreamWriter(fou);
try {
for (int i =0; i < list.getCount(); i++){
osw.append(list.getItemAtPosition(i).toString());
}
osw.flush();
osw.close();
Toast.makeText(getBaseContext(), "Saved", Toast.LENGTH_LONG).show();
} catch (IOException e){
e.printStackTrace();
}
} catch (FileNotFoundException e){
e.printStackTrace();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}
我的fragment_activity.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:background="@drawable/black_hd"
tools:context="com.example.wifiscanner.MainActivity$PlaceholderFragment" >
<ListView
android:id="@+id/listView1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="@+id/button1"
android:layout_centerHorizontal="true" >
</ListView>
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/listView1"
android:layout_alignParentTop="true"
android:layout_marginLeft="22dp"
android:minWidth="@dimen/abc_action_bar_progress_bar_size"
android:text="Scan" />
<Button
android:id="@+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_above="@+id/listView1"
android:layout_alignRight="@+id/listView1"
android:layout_marginRight="44dp"
android:text="Save" />
</RelativeLayout>
AndriodManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.scanner"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="19" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.CHANGE_WIFI_STATE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.scanner.MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
logcat的
06-04 00:59:25.940: D/dalvikvm(28589): GC_FOR_ALLOC freed 114K, 14% free 6895K/7943K, paused 26ms, total 27ms
06-04 00:59:25.970: I/dalvikvm-heap(28589): Grow heap (frag case) to 13.728MB for 6400016-byte allocation
06-04 00:59:26.150: D/dalvikvm(28589): GC_CONCURRENT freed 1K, 8% free 13144K/14215K, paused 63ms+10ms, total 181ms
06-04 00:59:26.150: D/dalvikvm(28589): WAIT_FOR_CONCURRENT_GC blocked 47ms
06-04 00:59:26.190: D/AbsListView(28589): Get MotionRecognitionManager
06-04 00:59:26.431: D/libEGL(28589): loaded /system/lib/egl/libGLES_rhea.so
06-04 00:59:26.501: D/BRCM_EGL(28589): eglCreateContext() config: 19 context: 0x4a088fb8, VC context 1, Thread 28589
06-04 00:59:26.501: D/BRCM_EGL(28589): eglCreateWindowSurface() surface: 0x4a0802f0, VC surface: 1, Thread: 28589
06-04 00:59:26.501: D/BRCM_EGL(28589): eglMakeCurrent(0x4a088fb8, 0x4a0802f0, 0x4a0802f0) Thread: 28589
06-04 00:59:26.511: D/OpenGLRenderer(28589): Enabling debug mode 0
06-04 00:59:31.035: D/AndroidRuntime(28589): Shutting down VM
06-04 00:59:31.035: W/dalvikvm(28589): threadid=1: thread exiting with uncaught exception (group=0x414f82a0)
06-04 00:59:31.075: E/AndroidRuntime(28589): FATAL EXCEPTION: main
06-04 00:59:31.075: E/AndroidRuntime(28589): java.lang.RuntimeException: Error receiving broadcast Intent { act=android.net.wifi.SCAN_RESULTS flg=0x8000010 } in com.example.scanner.MainActivity$WifiScanReceiver@41ca4fc0
06-04 00:59:31.075: E/AndroidRuntime(28589): at android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:766)
06-04 00:59:31.075: E/AndroidRuntime(28589): at android.os.Handler.handleCallback(Handler.java:615)
06-04 00:59:31.075: E/AndroidRuntime(28589): at android.os.Handler.dispatchMessage(Handler.java:92)
06-04 00:59:31.075: E/AndroidRuntime(28589): at android.os.Looper.loop(Looper.java:137)
06-04 00:59:31.075: E/AndroidRuntime(28589): at android.app.ActivityThread.main(ActivityThread.java:4947)
06-04 00:59:31.075: E/AndroidRuntime(28589): at java.lang.reflect.Method.invokeNative(Native Method)
06-04 00:59:31.075: E/AndroidRuntime(28589): at java.lang.reflect.Method.invoke(Method.java:511)
06-04 00:59:31.075: E/AndroidRuntime(28589): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1038)
06-04 00:59:31.075: E/AndroidRuntime(28589): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:805)
06-04 00:59:31.075: E/AndroidRuntime(28589): at dalvik.system.NativeStart.main(Native Method)
06-04 00:59:31.075: E/AndroidRuntime(28589): Caused by: java.lang.NullPointerException
06-04 00:59:31.075: E/AndroidRuntime(28589): at com.example.scanner.MainActivity$WifiScanReceiver.onReceive(MainActivity.java:119)
06-04 00:59:31.075: E/AndroidRuntime(28589): at android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:756)
06-04 00:59:31.075: E/AndroidRuntime(28589): ... 9 more
我不知道错误是什么，但我觉得它在BroadcastReciever中我编码20次扫描。如果你能帮助我，我会感激你..
答案 0 :(得分：0)
感谢您澄清这条线。您的问题是关于数组初始化：您初始化大小为scan_data的{{1}}数组，但在您在该特定命令之前说出
k s
null将初始化该行。之后，您的代码将适用于该部分。
另一个可疑的事情是，您使用 data[k] = new scan_data();
进行迭代，但每行都添加j。那不行。 AFAIK，您应该添加k++。