Question

Java 新手，正在学习从头开始构建计时器应用程序的教程。应用程序编译但在模拟器中按下启动或停止时应用程序崩溃。在没有通知的情况下启动崩溃应用程序，暂停崩溃应用程序并提供有关崩溃的通知并填写报告建议，停止不会崩溃但什么也不做。我已经搜索了多个关于它的网站，但似乎没有发现其中的问题。

main Activity java

package com.example.dayswithout;

import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.os.SystemClock;
import android.view.View;
import android.widget.Chronometer;
import android.widget.Toast;


public class MainActivity extends AppCompatActivity {
    private Chronometer chronometer;
    private long pauseOffset;
    private Boolean running;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        chronometer=findViewById(R.id.chronometer);
        chronometer.setFormat("Time: %s");
        chronometer.setBase(SystemClock.elapsedRealtime());
        chronometer.setOnChronometerTickListener(new Chronometer.OnChronometerTickListener() {
            @Override
            public void onChronometerTick(Chronometer chronometer) {
                if ((SystemClock.elapsedRealtime() - chronometer.getBase()) >= 10000) {
                    chronometer.setBase(SystemClock.elapsedRealtime());
                    Toast.makeText(MainActivity.this, "Bing!", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }
    public void startChronometer(View v){
        if(!running) {
            chronometer.setBase(SystemClock.elapsedRealtime()-pauseOffset);
            chronometer.start();
            running = true;
        }
    }
    public void pauseChronometer(View v){
        if(running) {
            chronometer.stop();
            pauseOffset=SystemClock.elapsedRealtime()-chronometer.getBase();
            running = false;
        }
    }
    public void resetChronometer(View v){
        chronometer.setBase(SystemClock.elapsedRealtime());
        pauseOffset=0;
    }
}

活动主xml


<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    tools:context=".MainActivity">

    <Chronometer
        android:id="@+id/chronometer"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="30sp" />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="startChronometer"
        android:text="Start"/>
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Pause"
        android:onClick="pauseChronometer"/>
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="reset"
        android:onClick="resetChronometer"/>
</LinearLayout>

日志

02/22 14:19:49: Launching 'app' on No Devices.
Install successfully finished in 1 s 718 ms.
$ adb shell am start -n "com.example.dayswithout/com.example.dayswithout.MainActivity" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER
Connected to process 6915 on device 'emulator-5554'.
Capturing and displaying logcat messages from application. This behavior can be disabled in the "Logcat output" section of the "Debugger" settings page.
I/ple.dayswithou: Not late-enabling -Xcheck:jni (already on)
I/ple.dayswithou: Unquickening 12 vdex files!
W/ple.dayswithou: Unexpected CPU variant for X86 using defaults: x86
D/NetworkSecurityConfig: No Network Security Config specified, using platform default
D/NetworkSecurityConfig: No Network Security Config specified, using platform default
D/libEGL: loaded /vendor/lib/egl/libEGL_emulation.so
D/libEGL: loaded /vendor/lib/egl/libGLESv1_CM_emulation.so
D/libEGL: loaded /vendor/lib/egl/libGLESv2_emulation.so
W/ple.dayswithou: Accessing hidden method Landroid/view/View;->computeFitSystemWindows(Landroid/graphics/Rect;Landroid/graphics/Rect;)Z (greylist, reflection, allowed)
W/ple.dayswithou: Accessing hidden method Landroid/view/ViewGroup;->makeOptionalFitsSystemWindows()V (greylist, reflection, allowed)
D/HostConnection: HostConnection::get() New Host Connection established 0xebb41ac0, tid 7013
D/HostConnection: HostComposition ext ANDROID_EMU_CHECKSUM_HELPER_v1 ANDROID_EMU_native_sync_v2 ANDROID_EMU_native_sync_v3 ANDROID_EMU_native_sync_v4 ANDROID_EMU_dma_v1 ANDROID_EMU_direct_mem ANDROID_EMU_host_composition_v1 ANDROID_EMU_host_composition_v2 ANDROID_EMU_vulkan ANDROID_EMU_deferred_vulkan_commands ANDROID_EMU_vulkan_null_optional_strings ANDROID_EMU_vulkan_create_resources_with_requirements ANDROID_EMU_YUV_Cache ANDROID_EMU_async_unmap_buffer ANDROID_EMU_vulkan_ignored_handles ANDROID_EMU_vulkan_free_memory_sync ANDROID_EMU_vulkan_shader_float16_int8 ANDROID_EMU_vulkan_async_queue_submit GL_OES_vertex_array_object GL_KHR_texture_compression_astc_ldr ANDROID_EMU_host_side_tracing ANDROID_EMU_async_frame_commands ANDROID_EMU_gles_max_version_2 
W/OpenGLRenderer: Failed to choose config with EGL_SWAP_BEHAVIOR_PRESERVED, retrying without...
D/EGL_emulation: eglCreateContext: 0xebb41a50: maj 2 min 0 rcv 2
D/EGL_emulation: eglMakeCurrent: 0xebb41a50: ver 2 0 (tinfo 0xebe96950) (first time)
I/Gralloc4: mapper 4.x is not supported
D/HostConnection: createUnique: call
    HostConnection::get() New Host Connection established 0xebb41eb0, tid 7013
D/goldfish-address-space: allocate: Ask for block of size 0x100
    allocate: ioctl allocate returned offset 0x3fbda9000 size 0x2000
D/HostConnection: HostComposition ext ANDROID_EMU_CHECKSUM_HELPER_v1 ANDROID_EMU_native_sync_v2 ANDROID_EMU_native_sync_v3 ANDROID_EMU_native_sync_v4 ANDROID_EMU_dma_v1 ANDROID_EMU_direct_mem ANDROID_EMU_host_composition_v1 ANDROID_EMU_host_composition_v2 ANDROID_EMU_vulkan ANDROID_EMU_deferred_vulkan_commands ANDROID_EMU_vulkan_null_optional_strings ANDROID_EMU_vulkan_create_resources_with_requirements ANDROID_EMU_YUV_Cache ANDROID_EMU_async_unmap_buffer ANDROID_EMU_vulkan_ignored_handles ANDROID_EMU_vulkan_free_memory_sync ANDROID_EMU_vulkan_shader_float16_int8 ANDROID_EMU_vulkan_async_queue_submit GL_OES_vertex_array_object GL_KHR_texture_compression_astc_ldr ANDROID_EMU_host_side_tracing ANDROID_EMU_async_frame_commands ANDROID_EMU_gles_max_version_2 
I/OpenGLRenderer: Davey! duration=1037ms; Flags=1, IntendedVsync=748790555628, Vsync=748807222294, OldestInputEvent=9223372036854775807, NewestInputEvent=0, HandleInputStart=748815462000, AnimationStart=748815491400, PerformTraversalsStart=748816913000, DrawStart=749730608800, SyncQueued=749763725800, SyncStart=749765306700, IssueDrawCommandsStart=749765382800, SwapBuffers=749827691200, FrameCompleted=749829712000, DequeueBufferDuration=138600, QueueBufferDuration=791000, GpuCompleted=-2920196950870201425, 
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.dayswithout, PID: 6915
    java.lang.IllegalStateException: Could not execute method for android:onClick
        at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:414)
        at android.view.View.performClick(View.java:7448)
        at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:1119)
        at android.view.View.performClickInternal(View.java:7425)
        at android.view.View.access$3600(View.java:810)
        at android.view.View$PerformClick.run(View.java:28305)
        at android.os.Handler.handleCallback(Handler.java:938)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:223)
        at android.app.ActivityThread.main(ActivityThread.java:7656)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
     Caused by: java.lang.reflect.InvocationTargetException
        at java.lang.reflect.Method.invoke(Native Method)
        at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:409)
        at android.view.View.performClick(View.java:7448) 
        at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:1119) 
        at android.view.View.performClickInternal(View.java:7425) 
        at android.view.View.access$3600(View.java:810) 
        at android.view.View$PerformClick.run(View.java:28305) 
        at android.os.Handler.handleCallback(Handler.java:938) 
        at android.os.Handler.dispatchMessage(Handler.java:99) 
        at android.os.Looper.loop(Looper.java:223) 
        at android.app.ActivityThread.main(ActivityThread.java:7656) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947) 
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.Boolean.booleanValue()' on a null object reference
        at com.example.dayswithout.MainActivity.startChronometer(MainActivity.java:35)
        at java.lang.reflect.Method.invoke(Native Method) 
        at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:409) 
        at android.view.View.performClick(View.java:7448) 
        at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:1119) 
        at android.view.View.performClickInternal(View.java:7425) 
        at android.view.View.access$3600(View.java:810) 
        at android.view.View$PerformClick.run(View.java:28305) 
        at android.os.Handler.handleCallback(Handler.java:938) 
        at android.os.Handler.dispatchMessage(Handler.java:99) 
        at android.os.Looper.loop(Looper.java:223) 
        at android.app.ActivityThread.main(ActivityThread.java:7656) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947) 
I/Process: Sending signal. PID: 6915 SIG: 9

Answer 1

这里有问题：

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.Boolean.booleanValue()' on a null object reference
        at com.example.dayswithout.MainActivity.startChronometer(MainActivity.java:35)

指的是 running 变量未初始化：

public void startChronometer(View v){
        if(!running) {

我建议从包装的 Boolean 更改它，该 null 是一个对象且未设置，因此它的值为 boolean。到声明中的原始 private Boolean running; -> private boolean running = false;：

class PluginFactory
    {
    public:
        // Instance of Factory
        static PluginFactory& Instance();
        void Register(IPluginRegistrar *Registrar, std::string name);
        
        IPlugin& GetPlugin(std::string name);

    private:
        std::unordered_map<std::string, IPluginRegistrar *>_registry;
        // private constructor, prevent copying
        PluginFactory() : _registry() {};
        PluginFactory(PluginFactoryconst&) = delete;
        void operator=(PluginFactoryconst&) = delete;
    };
    
    PluginFactory& PluginFactory::Instance()
    {
        static PluginFactoryinstance;
        return instance;
    }
    void PluginFactory::Register(IPluginRegistrar *registrar, std::string name)
    {
        if (_registry.count(name))
            std::cout << name << " is already registered!\n";
        else
        {
            std::cout << "Registering " << name << "\n";
            _registry[name] = registrar;
        }
    }
    IPlugin& PluginFactory::GetPlugin(std::string name)
    {
        IPluginRegistrar* registrar = _registry.at(name);        
        return registrar->GetPlugin();
    }
    #define REGISTER_PLUGIN(CLASSNAME) \
    namespace { \
    static MyNamespace::PluginRegistrar<CLASSNAME>\
    _registrar( #CLASSNAME ); \
    };

也可以将其设置为 false 以确保清晰（可选，因为 false 是默认值）。

Answer 2

错误表明您的对象未实例化：

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.Boolean.booleanValue()' on a null object reference

Boolean 是一个 Object 类型，一种引用类型，需要实例化。在您的情况下，private Boolean running; 已声明但从未实例化，导致上述 NullPointerException

相反，将类型从 Boolean 更改为原始 boolean。您不必初始化它，因为它将使用默认值 false。然而，为了可读性，初始化它可能是明智的

private boolean running = false;

计时器崩溃模拟器

2 个答案: