我正在尝试扫描接入点并列出它们。当我试图在模拟器中运行它时，没有错误，但应用程序停止工作消息进入屏幕。我尝试生成APK并开始真正的手机应用程序无法安装到手机。
这是我的代码：
package com.ahmet.apscan;
import android.app.Activity;
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.WifiManager;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends Activity implements View.OnClickListener{
WifiManager wifi;
ListView lv;
Button buttonScan;
int size = 0;
List<ScanResult> results;
String ITEM_KEY = "key";
ArrayList<String> arraylist = new ArrayList<>();
ArrayAdapter adapter;
/* Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
getActionBar().setTitle("Widhwan Setup Wizard");
setContentView(R.layout.activity_main);
buttonScan = (Button) findViewById(R.id.scan);
buttonScan.setOnClickListener(this);
lv = (ListView)findViewById(R.id.wifilist);
wifi = (WifiManager) getApplicationContext().getSystemService(Context.WIFI_SERVICE);
if (wifi.isWifiEnabled() == false)
{
Toast.makeText(getApplicationContext(), "wifi is disabled..making it enabled", Toast.LENGTH_LONG).show();
wifi.setWifiEnabled(true);
}
this.adapter = new ArrayAdapter<>(this,android.R.layout.simple_list_item_1,arraylist);
lv.setAdapter(this.adapter);
scanWifiNetworks();
}
public void onClick(View view)
{
scanWifiNetworks();
}
private void scanWifiNetworks(){
arraylist.clear();
registerReceiver(wifi_receiver, new IntentFilter(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));
wifi.startScan();
Log.d("WifScanner", "scanWifiNetworks");
Toast.makeText(this, "Scanning....", Toast.LENGTH_SHORT).show();
}
BroadcastReceiver wifi_receiver= new BroadcastReceiver()
{
@Override
public void onReceive(Context c, Intent intent)
{
Log.d("WifScanner", "onReceive");
results = wifi.getScanResults();
size = results.size();
unregisterReceiver(this);
try
{
while (size >= 0)
{
size--;
arraylist.add(results.get(size).SSID);
adapter.notifyDataSetChanged();
}
}
catch (Exception e)
{
Log.w("WifScanner", "Exception: "+e);
}
}
};
}
这是我的Xml：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:padding="10dp"
android:layout_width="match_parent"
android:layout_height="match_parent">
<ListView
android:id="@+id/wifilist"
android:layout_width="match_parent"
android:layout_height="312dp"
android:layout_weight="0.97" />
<Button
android:id="@+id/scan"
android:layout_width="match_parent"
android:layout_height="50dp"
android:layout_gravity="bottom"
android:layout_margin="15dp"
android:background="@android:color/holo_green_light"
android:text="Scan Again" />
这是我的logcat：
10-25 14:56:19.808 2010-4163/? I/GCoreUlr: Starting service, intent=Intent { act=com.google.android.location.reporting.ACTION_UPDATE_WORLD cmp=com.google.android.gms/com.google.android.location.reporting.service.DispatchingService (has extras) }, extras=Bundle[{receiverAction=com.google.android.location.reporting.PHENOTYPE_FLAGS_CHANGED}]
10-25 14:56:19.812 2010-4137/? I/GCoreUlr: WorldUpdater received intent Intent { act=com.google.android.location.reporting.ACTION_UPDATE_WORLD cmp=com.google.android.gms/com.google.android.location.reporting.service.DispatchingService (has extras) } with receiverAction com.google.android.location.reporting.PHENOTYPE_FLAGS_CHANGED
10-25 14:56:19.813 2010-4137/? E/GCoreUlr: Bad errorId configuring silent feedback
10-25 14:56:19.814 2010-4137/? I/GCoreUlr: WorldUpdater:com.google.android.location.reporting.PHENOTYPE_FLAGS_CHANGED: Ensuring that reporting is stopped because of reasons: (no Google accounts)
10-25 14:56:19.817 2010-4137/? I/GCoreUlr: Unbound from all location providers
10-25 14:56:19.817 2010-4137/? I/GCoreUlr: Place inference reporting - stop
10-25 14:56:19.819 2010-2010/? I/GCoreUlr: DispatchingService.onDestroy()
10-25 14:56:19.819 2010-2010/? I/GCoreUlr: Stopping handler for UlrDispSvcFast
10-25 14:56:19.822 2010-2010/? I/GCoreUlr: Unbound from all location providers
10-25 14:56:19.822 2010-2010/? I/GCoreUlr: Place inference reporting - stop
如何修复此错误配置无提示反馈？
现在我尝试了Clean Project＆amp;制作项目。之后我建立了新的模拟器和 logcat改变了这样;
10-25 15:21:22.302 4752-4752/? I/art: Not late-enabling -Xcheck:jni (already on)
10-25 15:21:22.302 4752-4752/? W/art: Unexpected CPU variant for X86 using defaults: x86
10-25 15:21:22.317 4752-4759/? E/art: Failed sending reply to debugger: Broken pipe
10-25 15:21:22.317 4752-4759/? I/art: Debugger is no longer active
10-25 15:21:22.317 4752-4759/? I/art: Starting a blocking GC Instrumentation
10-25 15:21:22.391 4752-4752/? W/System: ClassLoader referenced unknown path: /data/app/com.ahmet.apscan-2/lib/x86
10-25 15:21:22.396 4752-4752/? I/InstantRun: starting instant run server: is main process
10-25 15:21:22.414 4752-4752/? D/AndroidRuntime: Shutting down VM
10-25 15:21:22.414 4752-4752/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.ahmet.apscan, PID: 4752
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.ahmet.apscan/com.ahmet.apscan.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setTitle(java.lang.CharSequence)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setTitle(java.lang.CharSequence)' on a null object reference
at com.ahmet.apscan.MainActivity.onCreate(MainActivity.java:41)
at android.app.Activity.performCreate(Activity.java:6662)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
答案 0 :(得分：0)
使用getSupportActionBar()代替getActionBar()。另外，请在setContentView()行以下指定。
答案 1 :(得分：0)
所有关于你的getActionBar（），它似乎与this相关 检查此链接中的所有内容。
答案 2 :(得分：0)
取决于帖子的更新 使用
getSupportActionBar().setTitle("Widhwan Setup Wizard");
并将其置于setContentView方法下
所以你的代码应该是这样的
setContentView(R.layout.activity_main);
getSupportActionBar().setTitle("Widhwan Setup Wizard");
答案 3 :(得分：0)
我认为您在Android版lolipop或更高版本上运行该应用程序。所以
使用com.android.support:appcompat-v7库
更改
public class MainActivity extends Activity implements View.OnClickListener
到
public class MainActivity extends AppCompatActivity implements View.OnClickListener
并更改
getActionBar().setTitle("Widhwan Setup Wizard");
setContentView(R.layout.activity_main);
到
setContentView(R.layout.activity_main);
getSupportActionBar().setTitle("Widhwan Setup Wizard");