我正在执行一个使用按钮打开另一个活动的基本任务。代码似乎没有错误，但应用程序崩溃甚至没有显示主要活动。这在模拟器和我的设备上都会发生。 当应用程序没有功能时，即当应用程序只有按钮什么都不做时，应用程序工作正常。但是，如果我尝试让他们做任何事情（打算开放另一个活动，或玩他们的可见性）应用程序崩溃。 logcat如下：
11-12 13:55:56.627 2962-2962/? D/AndroidRuntime: >>>>>> START com.android.internal.os.RuntimeInit uid 0 <<<<<<
11-12 13:55:56.628 2962-2962/? D/AndroidRuntime: CheckJNI is ON
11-12 13:55:56.672 2962-2962/? D/ICU: No timezone override file found: /data/misc/zoneinfo/current/icu/icu_tzdata.dat
11-12 13:55:56.754 2962-2962/? E/memtrack: Couldn't load memtrack module (No such file or directory)
11-12 13:55:56.754 2962-2962/? E/android.os.Debug: failed to load memtrack module: -2
11-12 13:55:56.755 2962-2962/? I/Radio-JNI: register_android_hardware_Radio DONE
11-12 13:55:56.761 2962-2962/? D/AndroidRuntime: Calling main entry com.android.commands.pm.Pm
11-12 13:55:56.772 2962-2962/? I/art: System.exit called, status: 0
11-12 13:55:56.772 2962-2962/? I/AndroidRuntime: VM exiting with result code 0.
11-12 13:55:57.068 2977-2977/? D/AndroidRuntime: >>>>>> START com.android.internal.os.RuntimeInit uid 0 <<<<<<
11-12 13:55:57.069 2977-2977/? D/AndroidRuntime: CheckJNI is ON
11-12 13:55:57.129 2977-2977/? D/ICU: No timezone override file found: /data/misc/zoneinfo/current/icu/icu_tzdata.dat
11-12 13:55:57.199 2977-2977/? E/memtrack: Couldn't load memtrack module (No such file or directory)
11-12 13:55:57.199 2977-2977/? E/android.os.Debug: failed to load memtrack module: -2
11-12 13:55:57.200 2977-2977/? I/Radio-JNI: register_android_hardware_Radio DONE
11-12 13:55:57.205 2977-2977/? D/AndroidRuntime: Calling main entry com.android.commands.pm.Pm
11-12 13:55:57.216 2977-2977/? I/art: System.exit called, status: 0
11-12 13:55:57.220 2977-2977/? I/AndroidRuntime: VM exiting with result code 0.
11-12 13:55:59.484 2987-2987/? D/AndroidRuntime: >>>>>> START com.android.internal.os.RuntimeInit uid 0 <<<<<<
11-12 13:55:59.487 2987-2987/? D/AndroidRuntime: CheckJNI is ON
11-12 13:55:59.522 2987-2987/? D/ICU: No timezone override file found: /data/misc/zoneinfo/current/icu/icu_tzdata.dat
11-12 13:55:59.602 2987-2987/? E/memtrack: Couldn't load memtrack module (No such file or directory)
11-12 13:55:59.602 2987-2987/? E/android.os.Debug: failed to load memtrack module: -2
11-12 13:55:59.603 2987-2987/? I/Radio-JNI: register_android_hardware_Radio DONE
11-12 13:55:59.615 2987-2987/? D/AndroidRuntime: Calling main entry com.android.commands.wm.Wm
11-12 13:55:59.643 2987-2987/? D/AndroidRuntime: Shutting down VM
11-12 13:56:01.407 2999-2999/? D/AndroidRuntime: >>>>>> START com.android.internal.os.RuntimeInit uid 0 <<<<<<
11-12 13:56:01.408 2999-2999/? D/AndroidRuntime: CheckJNI is ON
11-12 13:56:01.465 2999-2999/? D/ICU: No timezone override file found: /data/misc/zoneinfo/current/icu/icu_tzdata.dat
11-12 13:56:01.542 2999-2999/? E/memtrack: Couldn't load memtrack module (No such file or directory)
11-12 13:56:01.542 2999-2999/? E/android.os.Debug: failed to load memtrack module: -2
11-12 13:56:01.543 2999-2999/? I/Radio-JNI: register_android_hardware_Radio DONE
11-12 13:56:01.553 2999-2999/? D/AndroidRuntime: Calling main entry com.android.commands.am.Am
--------- beginning of system
11-12 13:56:01.562 1585-1920/system_process I/ActivityManager: START u0 {act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=com.example.dell.crash/.MainActivity} from uid 0 on display 0
11-12 13:56:01.579 2147-2341/com.google.android.googlequicksearchbox:search I/MicrophoneInputStream: mic_close com.google.android.apps.gsa.speech.audio.u@20f33e2
11-12 13:56:01.605 3007-3007/? I/art: Not late-enabling -Xcheck:jni (already on)
11-12 13:56:01.606 2147-2347/com.google.android.googlequicksearchbox:search I/HotwordRecognitionRnr: Stopping hotword detection.
11-12 13:56:01.606 2147-2699/com.google.android.googlequicksearchbox:search I/HotwordRecognitionRnr: Hotword detection finished
11-12 13:56:01.610 1585-1598/system_process I/ActivityManager: Start proc 3007:com.example.dell.crash/u0a64 for activity com.example.dell.crash/.MainActivity
11-12 13:56:01.604 2999-2999/? D/AndroidRuntime: Shutting down VM
[ 11-12 13:56:01.697 1585: 1608 D/ ]
HostConnection::get() New Host Connection established 0x7f8480e69e40, tid 1608
11-12 13:56:01.728 3007-3007/com.example.dell.crash W/System: ClassLoader referenced unknown path: /data/app/com.example.dell.crash-1/lib/x86_64
11-12 13:56:01.729 3007-3007/com.example.dell.crash I/InstantRun: Instant Run Runtime started. Android package is com.example.dell.crash, real application class is null.
11-12 13:56:02.906 1891-2316/com.google.android.googlequicksearchbox E/Surface: getSlotFromBufferLocked: unknown buffer: 0xe9e5e990
11-12 13:56:03.510 3007-3007/com.example.dell.crash W/System: ClassLoader referenced unknown path: /data/app/com.example.dell.crash-1/lib/x86_64
11-12 13:56:03.707 3007-3007/com.example.dell.crash D/AndroidRuntime: Shutting down VM
--------- beginning of crash
11-12 13:56:03.707 3007-3007/com.example.dell.crash E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.dell.crash, PID: 3007
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.dell.crash/com.example.dell.crash.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2327)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
at android.support.v7.app.AppCompatDelegateImplBase.<init>(AppCompatDelegateImplBase.java:116)
at android.support.v7.app.AppCompatDelegateImplV9.<init>(AppCompatDelegateImplV9.java:147)
at android.support.v7.app.AppCompatDelegateImplV11.<init>(AppCompatDelegateImplV11.java:27)
at android.support.v7.app.AppCompatDelegateImplV14.<init>(AppCompatDelegateImplV14.java:50)
at android.support.v7.app.AppCompatDelegateImplV23.<init>(AppCompatDelegateImplV23.java:29)
at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:199)
at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:181)
at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:521)
at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:190)
at com.example.dell.crash.MainActivity.<init>(MainActivity.java:10)
at java.lang.Class.newInstance(Native Method)
at android.app.Instrumentation.newActivity(Instrumentation.java:1067)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2317)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
11-12 13:56:03.708 1585-2055/system_process W/ActivityManager: Force finishing activity com.example.dell.crash/.MainActivity
11-12 13:56:04.016 1585-2055/system_process I/WindowManager: Screenshot max retries 4 of Token{9795bf6 ActivityRecord{989c091 u0 com.example.dell.crash/.MainActivity t51 f}} appWin=Window{a3bf3ce u0 Starting com.example.dell.crash} drawState=4
11-12 13:56:04.116 1585-2485/system_process I/OpenGLRenderer: Initialized EGL, version 1.4
11-12 13:56:04.518 1585-1601/system_process W/ActivityManager: Activity pause timeout for ActivityRecord{989c091 u0 com.example.dell.crash/.MainActivity t51 f}
11-12 13:56:04.550 2328-2336/com.google.android.gms W/SQLiteConnectionPool: A SQLiteConnection object for database '/data/user/0/com.google.android.gms/databases/networkstatistics.sqlite' was leaked! Please fix your application to end transactions in progress properly and to close the database when it is no longer needed.
11-12 13:56:04.550 2328-2336/com.google.android.gms W/SQLiteConnectionPool: A SQLiteConnection object for database '/data/user/0/com.google.android.gms/databases/metrics.db' was leaked! Please fix your application to end transactions in progress properly and to close the database when it is no longer needed.
11-12 13:56:04.551 2328-2336/com.google.android.gms W/SQLiteConnectionPool: A SQLiteConnection object for database '/data/user/0/com.google.android.gms/databases/help_responses.db' was leaked! Please fix your application to end transactions in progress properly and to close the database when it is no longer needed.
11-12 13:56:04.572 2328-2336/com.google.android.gms W/SQLiteConnectionPool: A SQLiteConnection object for database '/data/user/0/com.google.android.gms/databases/auto_complete_suggestions.db' was leaked! Please fix your application to end transactions in progress properly and to close the database when it is no longer needed.
11-12 13:56:04.860 1585-1602/system_process I/Choreographer: Skipped 35 frames! The application may be doing too much work on its main thread.
11-12 13:56:04.925 2147-3076/com.google.android.googlequicksearchbox:search I/HotwordRecognitionRnr: Starting hotword detection.
11-12 13:56:04.943 2147-3078/com.google.android.googlequicksearchbox:search I/MicrophoneInputStream: mic_starting com.google.android.apps.gsa.speech.audio.u@76753fd
11-12 13:56:04.955 1585-1599/system_process I/ActivityManager: Killing 2527:com.android.settings/1000 (adj 15): empty #17
11-12 13:56:04.965 1202-2042/? E/audio_hw_generic: Error opening input stream format 1, channel_mask 0010, sample_rate 16000
11-12 13:56:04.969 1202-3080/? I/AudioFlinger: AudioFlinger's thread 0xf3b80000 ready to run
11-12 13:56:04.988 2147-3078/com.google.android.googlequicksearchbox:search I/MicrophoneInputStream: mic_started com.google.android.apps.gsa.speech.audio.u@76753fd
11-12 13:56:04.991 2147-2341/com.google.android.googlequicksearchbox:search I/MicrophoneInputStream: mic_close com.google.android.apps.gsa.speech.audio.u@76753fd
11-12 13:56:04.992 2147-3078/com.google.android.googlequicksearchbox:search E/AudioRecord-JNI: Error -4 during AudioRecord native read
11-12 13:56:05.009 2147-2347/com.google.android.googlequicksearchbox:search I/HotwordRecognitionRnr: Stopping hotword detection.
11-12 13:56:05.010 2147-3076/com.google.android.googlequicksearchbox:search I/HotwordRecognitionRnr: Hotword detection finished
11-12 13:56:05.140 1585-1599/system_process I/ActivityManager: Killing 2649:com.android.dialer/u0a4 (adj 15): empty #17
11-12 13:56:05.395 1891-2316/com.google.android.googlequicksearchbox W/OpenGLRenderer: Incorrectly called buildLayer on View: em, destroying layer...
11-12 13:56:05.447 1585-1608/system_process D/gralloc_ranchu: gralloc_unregister_buffer: exiting HostConnection (is buffer-handling thread)
11-12 13:56:05.466 2328-2472/com.google.android.gms I/Icing: Usage reports 0 indexed 0 rejected 0 imm upload true
11-12 13:56:05.486 2328-2504/com.google.android.gms I/Icing: Usage reports 0 indexed 0 rejected 0 imm upload true
11-12 13:56:05.499 1585-1920/system_process I/ActivityManager: Killing 2670:com.android.managedprovisioning/u0a8 (adj 15): empty #17
11-12 13:56:15.034 1585-1601/system_process W/ActivityManager: Activity destroy timeout for ActivityRecord{989c091 u0 com.example.dell.crash/.MainActivity t51 f}
11-12 13:56:15.075 2147-3230/com.google.android.googlequicksearchbox:search W/CronetSyncConnectionRcs: Upload content type not set.
11-12 13:56:17.062 3007-3007/com.example.dell.crash I/Process: Sending signal. PID: 3007 SIG: 9
11-12 13:56:17.093 1585-2485/system_process E/Surface: getSlotFromBufferLocked: unknown buffer: 0x7f849297e160
11-12 13:56:17.101 1585-2485/system_process D/OpenGLRenderer: endAllStagingAnimators on 0x7f84835bfc00 (RippleDrawable) with handle 0x7f847ee9ee60
11-12 13:56:17.131 1585-1920/system_process W/InputMethodManagerService: Window already focused, ignoring focus gain of: com.android.internal.view.IInputMethodClient$Stub$Proxy@9d97b24 attribute=null, token = android.os.BinderProxy@32922a9
11-12 13:56:17.165 1585-1920/system_process I/ActivityManager: Process com.example.dell.crash (pid 3007) has died
11-12 13:56:17.367 1585-1608/system_process W/AppOps: Finishing op nesting under-run: uid 1000 pkg android code 24 time=0 duration=0 nesting=0
11-12 13:56:17.409 2147-3268/com.google.android.googlequicksearchbox:search I/HotwordRecognitionRnr: Starting hotword detection.
11-12 13:56:17.413 2147-3269/com.google.android.googlequicksearchbox:search I/MicrophoneInputStream: mic_starting com.google.android.apps.gsa.speech.audio.u@898b349
11-12 13:56:17.423 1202-1546/? E/audio_hw_generic: Error opening input stream format 1, channel_mask 0010, sample_rate 16000
11-12 13:56:17.444 1202-3273/? I/AudioFlinger: AudioFlinger's thread 0xf3b80000 ready to run
11-12 13:56:17.449 2147-2157/com.google.android.googlequicksearchbox:search I/art: Background sticky concurrent mark sweep GC freed 1466(93KB) AllocSpace objects, 0(0B) LOS objects, 9% free, 4MB/4MB, paused 25.294ms total 31.038ms
11-12 13:56:17.456 2147-3269/com.google.android.googlequicksearchbox:search I/MicrophoneInputStream: mic_started com.google.android.apps.gsa.speech.audio.u@898b349
11-12 13:56:17.493 2147-2147/com.google.android.googlequicksearchbox:search I/HotwordWorker: onReady
11-12 13:56:17.504 2328-3272/com.google.android.gms W/IcingInternalCorpora: getNumBytesRead when not calculated.
11-12 13:56:17.564 2328-2472/com.google.android.gms I/Icing: Usage reports 0 indexed 0 rejected 0 imm upload true
11-12 13:56:17.571 2328-2472/com.google.android.gms I/Icing: Usage reports 0 indexed 0 rejected 0 imm upload true
11-12 13:56:18.155 1202-1544/? W/AudioFlinger: write blocked for 408 msecs, 4 delayed writes, thread 0xf4500000
.java文件包含以下块：
public class MainActivity extends AppCompatActivity {
Button btn1 = (Button) findViewById(R.id.button);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btn1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(MainActivity.this, Main2Activity.class));
}
});
}
}
XML文件如下：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.dell.crash.MainActivity">
<Button
android:text="Button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="102dp"
android:id="@+id/button" />
</RelativeLayout>
我正在使用Android Studio 2.2.2
答案 0 :(得分：1)
之后
setContentView(R.layout.activity_main);
像这样添加电话
Button button = (Button) findViewById(R.id.button);
问题是你没有为按钮创建参考。
答案 1 :(得分：1)
将Button btn1 = (Button) findViewById(R.id.button);放入oncreate方法。
原因是您尝试向按钮添加事件，但未在oncreate内显示每个应用开始其活动的位置的参考ID。
答案 2 :(得分：0)
你应该始终在onCreate（）中实例化按钮。所以你的代码应该像
public class MainActivity extends AppCompatActivity {
Button btn1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btn1 = (Button) findViewById(R.id.button);
btn1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(MainActivity.this, Main2Activity.class));
}
});
}
}
答案 3 :(得分：0)
如果在声明部分中初始化btn1变量，它将在setContextView(...)函数调用之前运行。在btn1之后放置setContextView(...)初始化！
public class MainActivity extends AppCompatActivity {
private Button btn1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btn1 = Button.class.cast(findViewById(R.id.button));
btn1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(MainActivity.this, Main2Activity.class));
}
});
}
}