计时器使模拟器崩溃

Question

java新手，正在学习从头开始构建计时器应用程序的教程。该应用程序可编译，但当在模拟器中按下"开始"或"停止"时，该应用程序将崩溃。在没有通知的情况下启动崩溃的应用程序，暂停带有崩溃通知的崩溃应用程序并填写报告建议，stop不会崩溃，但什么也不做。我已经搜索了很多关于它的网站，似乎没有发现任何问题。

主活动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

这里有一个问题：

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)

表示running变量未初始化：

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

我建议将它从一个包装的Boolean更改为一个对象，而不是设置，所以它的值是null。到声明中的基元boolean：

private Boolean running;
->
private boolean running = false;

对于clarity，可以将其设置为false(可选，因为false是默认值)。

Answer 2

错误表明您的对象没有实例化：

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，一个引用类型，需要实例化。在您的情况下，声明了private Boolean running;，但它从未实例化，从而导致上面的NullPointerException

相反，将类型从Boolean更改为原始boolean。您不需要来初始化它，因为它将使用默认值false。然而，为了可读性，启动可能是明智的

private boolean running = false;