运行 Flutter App 时出现 java.lang.NullPointerException

Question

运行我从 Github 检出的开源 Flutter 应用程序时，出现以下错误。它运行屏幕的第一个 Activity，大约 1 秒后应用程序崩溃并在 Logcat 中出现以下错误。我在 Flutter 的运行控制台中看不到任何错误。

Process: app.ceylon.selftrackingapp, PID: 32590
    java.lang.RuntimeException: Unable to start activity ComponentInfo{app.ceylon.selftrackingapp/app.ceylon.selftrackingapp.MainActivity}: java.lang.NullPointerException: Attempt to invoke interface method 'void io.flutter.plugin.common.BinaryMessenger.setMessageHandler(java.lang.String, io.flutter.plugin.common.BinaryMessenger$BinaryMessageHandler)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3448)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3595)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2147)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:237)
        at android.app.ActivityThread.main(ActivityThread.java:7811)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1076)
     Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'void io.flutter.plugin.common.BinaryMessenger.setMessageHandler(java.lang.String, io.flutter.plugin.common.BinaryMessenger$BinaryMessageHandler)' on a null object reference
        at io.flutter.plugin.common.MethodChannel.setMethodCallHandler(MethodChannel.java:116)
        at com.baseflow.geolocator.GeolocatorPlugin.registerWith(GeolocatorPlugin.java:49)
        at io.flutter.plugins.GeneratedPluginRegistrant.registerWith(GeneratedPluginRegistrant.java:20)
        at app.ceylon.selftrackingapp.MainActivity.onCreate(MainActivity.kt:32)
        at android.app.Activity.performCreate(Activity.java:7955)
        at android.app.Activity.performCreate(Activity.java:7944)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1307)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3423)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3595) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2147) 
        at android.os.Handler.dispatchMessage(Handler.java:107) 
        at android.os.Looper.loop(Looper.java:237) 
        at android.app.ActivityThread.main(ActivityThread.java:7811) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1076) 
2020-03-21 10:09:53.328 15534-15539/? E/nightwatch-watcher: Failed to read from logcat: Success

我正在使用实际设备 Galaxy S9+ 进行测试，这是我在我的计算机中安装的 Flutter 版本。

Flutter 1.15.17 • channel beta • https://github.com/flutter/flutter.git
Framework • revision 2294d75bfa (2 weeks ago) • 2020-03-07 00:28:38 +0900
Engine • revision 5aff311948
Tools • Dart 2.8.0 (build 2.8.0-dev.12.0 9983424a3c)

Answer 1

我也寻找过解决方案，并在这里找到了一个。

核心是：在pubspec.yaml中添加“ flutter_plugin_android_lifecycle: ^1.0.4”