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android - WifiAwareManager 返回 null

问题描述

我正在尝试创建一个使用 Wifi Aware 但我的 WifiAwareManager 返回 null 的应用程序。如何正确初始化类以使其不返回 null？这种行为的原因是什么？我很确定 Pixel 2 XL 确实支持 Wifi Aware，我错了吗？

final WifiAwareManager wifiAwareManager = (WifiAwareManager) getSystemService(Context.WIFI_AWARE_SERVICE);

if (wifiAwareManager.isAvailable()) {
    System.out.println("aware avaiable");
} else {
    System.out.println("aware not avaiable");
}

日志是：

2018-10-11 12:45:53.926 4003-4003/com.example.lucapalmieri.awarecheckE/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.lucapalmieri.awarecheck, PID: 4003
java.lang.IllegalStateException: Could not execute method for android:onClick
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:389)
    at android.view.View.performClick(View.java:6294)
    at android.view.View$PerformClick.run(View.java:24770)
    at android.os.Handler.handleCallback(Handler.java:790)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:164)
    at android.app.ActivityThread.main(ActivityThread.java:6494)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
 Caused by: java.lang.reflect.InvocationTargetException
    at java.lang.reflect.Method.invoke(Native Method)
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:384)
    at android.view.View.performClick(View.java:6294) 
    at android.view.View$PerformClick.run(View.java:24770) 
    at android.os.Handler.handleCallback(Handler.java:790) 
    at android.os.Handler.dispatchMessage(Handler.java:99) 
    at android.os.Looper.loop(Looper.java:164) 
    at android.app.ActivityThread.main(ActivityThread.java:6494) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807) 
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.net.wifi.aware.WifiAwareManager.isAvailable()' on a null object reference
    at com.example.lucapalmieri.awarecheck.MainActivity.check(MainActivity.java:71)
    at java.lang.reflect.Method.invoke(Native Method) 
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:384) 
    at android.view.View.performClick(View.java:6294) 
    at android.view.View$PerformClick.run(View.java:24770) 
    at android.os.Handler.handleCallback(Handler.java:790) 
    at android.os.Handler.dispatchMessage(Handler.java:99) 
    at android.os.Looper.loop(Looper.java:164) 
    at android.app.ActivityThread.main(ActivityThread.java:6494) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807) 

标签： androidnullpointerexceptionandroid-wifi

解决方案

原因 isAvailiable 仅从 api 级别 26 添加为 WifiAwareManager。我假设您使用的 android 版本低于 Android 8.0 https://developer.android.com/reference/android/net/wifi/aware/WifiAwareManager.html#isAvailable()

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