我有一个错误，我已经在堆栈上留下了大约一小时的痕迹，我无法弄清楚我做错了什么。
这最终将控制机器人并包含更多功能，但我现在正在做的是确保手机连接到机器人的wifi网络。我是通过测试页面（192.168.240.1/handshake）并查看它返回的内容来做到这一点的。目前，当我连接到机器人时，它可以正常工作，但如果我没有连接它，它会崩溃。我试图评论我的很多代码，但问题仍然存在。
package com.ruralsurvivor.robotcontrolapp;
import android.content.Context;
import android.content.Intent;
import android.graphics.Color;
import android.net.wifi.WifiInfo;
import android.net.wifi.WifiManager;
import android.os.Bundle;
import android.os.Handler;
import android.provider.Settings;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.webkit.WebView;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;
import java.util.concurrent.ExecutionException;
public class MainActivity extends AppCompatActivity {
TextView t;
TextView t2;
Button b;
String z;
String lResponse;
private Handler handler = new Handler();
public Runnable runnable = new Runnable() {
@Override
public void run() {
update();
handler.postDelayed(runnable, 50);
}
public void update() {
int numberOfLevels = 100;
android.net.wifi.WifiManager wifiManager = (WifiManager) getSystemService(WIFI_SERVICE);
WifiInfo wifiInfo = wifiManager.getConnectionInfo();
int level = WifiManager.calculateSignalLevel(wifiInfo.getRssi(), numberOfLevels);
ProgressBar firstBar = (ProgressBar) findViewById(R.id.determinateBar);
firstBar.setProgress(level);
wifiManager = (WifiManager) getSystemService(Context.WIFI_SERVICE);
WifiInfo info = wifiManager.getConnectionInfo();
String ssid = info.getSSID();
t.setText("Network: " + ssid);
z = "http://192.168.240.1/handshake";
try {
lResponse = new HTTPRequest().execute(z).get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
} catch (NullPointerException e) {
e.printStackTrace();
lResponse = "error";
}
if (!lResponse.equals("Schmuck me sideways")) {
b.setEnabled(false);
b.setAlpha(0.75f);
t2.setTextColor(Color.parseColor("#c10508"));
t2.setText("Not Connected");
} else {
b.setEnabled(true);
b.setAlpha(1f);
t2.setTextColor(Color.parseColor("#1eb500"));
t2.setText("Connected");
}
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
t = new TextView(this);
t=(TextView)findViewById(R.id.textView2);
t2 = new TextView(this);
t2 =(TextView)findViewById(R.id.textView3);
b=(Button)findViewById(R.id.button2);
start();
}
public void start() {
runnable.run();
}
public void onClick(View view) {
Intent intent = new Intent(Settings.ACTION_WIFI_SETTINGS);
startActivity(intent);
}
public void clickMe(View v) {
handler.removeCallbacks(runnable);
setContentView(R.layout.control);
WebView myWebView = (WebView) findViewById(R.id.webView);
myWebView.loadUrl("http://192.168.240.1:8080/?action=stream");
}
}
这是我的堆栈跟踪：
07-06 23:21:15.713 18517-18517/com.ruralsurvivor.robotcontrolapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.ruralsurvivor.robotcontrolapp, PID: 18517
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.ruralsurvivor.robotcontrolapp/com.ruralsurvivor.robotcontrolapp.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2198)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2257)
at android.app.ActivityThread.access$800(ActivityThread.java:139)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5097)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.ruralsurvivor.robotcontrolapp.MainActivity$1.update(MainActivity.java:57)
at com.ruralsurvivor.robotcontrolapp.MainActivity$1.run(MainActivity.java:34)
at com.ruralsurvivor.robotcontrolapp.MainActivity.start(MainActivity.java:83)
at com.ruralsurvivor.robotcontrolapp.MainActivity.onCreate(MainActivity.java:79)
at android.app.Activity.performCreate(Activity.java:5248)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1110)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2162)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2257)
at android.app.ActivityThread.access$800(ActivityThread.java:139)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5097)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
这是我用来测试wifi的代码：
package com.ruralsurvivor.robotcontrolapp;
import android.os.AsyncTask;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
public class HTTPRequest extends AsyncTask< String, String, String >
{
protected String theHTTPString = null;
@Override
protected String doInBackground( String... uri )
{
URL url = null;
try
{
url = new URL( uri[0] );
}
catch( MalformedURLException e )
{
e.printStackTrace();
}
String responseString = null;
try
{
HttpURLConnection httpclient = (HttpURLConnection) url.openConnection();
int lResponseCode = httpclient.getResponseCode();
if( lResponseCode != HttpURLConnection.HTTP_OK )
{
httpclient.disconnect();
throw new IOException( "RESPONSE REJECTED WITH ERROR CODE: " + lResponseCode );
}
BufferedReader in = new BufferedReader(new InputStreamReader( httpclient.getInputStream() ));
StringBuffer lStringBuffer = new StringBuffer();
String inputLine;
while( (inputLine = in.readLine()) != null )
{
lStringBuffer.append( inputLine );
}
httpclient.disconnect();
in.close();
responseString = lStringBuffer.toString();
}
catch( IOException e )
{
e.printStackTrace();
return responseString;
}
theHTTPString = responseString;
return responseString;
}
}