单击导航到新活动的按钮图标后，Android应用程序崩溃[重复]

【问题标题】：Android application crashes after clicking the button icon that navigates to a new activity [duplicate]单击导航到新活动的按钮图标后，Android应用程序崩溃[重复]
【发布时间】：2021-03-04 01:19:35
【问题描述】：

我遇到了一个问题，当我单击 action_add_event 图标按钮以在 tge EventDetails 活动中添加新事件时程序崩溃。 EventDetails 活动询问事件的详细信息，数据将被存储到数据库中，并被传输回 MainActivity 进行显示。

这是应用崩溃时的 logcat

2020-11-20 23:31:45.778 1993-1993/? I/.eventcountdow: Not late-enabling -Xcheck:jni (already on)
2020-11-20 23:31:45.847 1993-1993/? E/.eventcountdow: Unknown bits set in runtime_flags: 0x8000
2020-11-20 23:31:45.848 1993-1993/? W/.eventcountdow: Unexpected CPU variant for X86 using defaults: x86
2020-11-20 23:31:46.491 1993-1993/com.example.eventcountdown W/RenderThread: type=1400 audit(0.0:423): avc: denied { write } for name="property_service" dev="tmpfs" ino=6750 scontext=u:r:untrusted_app:s0:c140,c256,c512,c768 tcontext=u:object_r:property_socket:s0 tclass=sock_file permissive=0
2020-11-20 23:31:46.496 1993-2019/com.example.eventcountdown D/libEGL: Emulator has host GPU support, qemu.gles is set to 1.
2020-11-20 23:31:46.498 1993-2019/com.example.eventcountdown W/libc: Unable to set property "qemu.gles" to "1": connection failed; errno=13 (Permission denied)
2020-11-20 23:31:46.560 1993-2019/com.example.eventcountdown D/libEGL: loaded /vendor/lib/egl/libEGL_emulation.so
2020-11-20 23:31:46.562 1993-2019/com.example.eventcountdown D/libEGL: loaded /vendor/lib/egl/libGLESv1_CM_emulation.so
2020-11-20 23:31:46.619 1993-2019/com.example.eventcountdown D/libEGL: loaded /vendor/lib/egl/libGLESv2_emulation.so
2020-11-20 23:31:47.007 1993-1993/com.example.eventcountdown W/.eventcountdow: Accessing hidden method Landroid/view/View;->computeFitSystemWindows(Landroid/graphics/Rect;Landroid/graphics/Rect;)Z (greylist, reflection, allowed)
2020-11-20 23:31:47.008 1993-1993/com.example.eventcountdown W/.eventcountdow: Accessing hidden method Landroid/view/ViewGroup;->makeOptionalFitsSystemWindows()V (greylist, reflection, allowed)
2020-11-20 23:31:47.205 1993-2017/com.example.eventcountdown D/HostConnection: HostConnection::get() New Host Connection established 0xd784ffa0, tid 2017
2020-11-20 23:31:47.241 1993-2017/com.example.eventcountdown 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_YUV420_888_to_NV21 ANDROID_EMU_YUV_Cache ANDROID_EMU_async_unmap_buffer ANDROID_EMU_vulkan_free_memory_sync ANDROID_EMU_vulkan_shader_float16_int8 ANDROID_EMU_vulkan_async_queue_submit GL_OES_EGL_image_external_essl3 GL_OES_vertex_array_object GL_KHR_texture_compression_astc_ldr ANDROID_EMU_gles_max_version_3_0 
2020-11-20 23:31:47.245 1993-2017/com.example.eventcountdown W/OpenGLRenderer: Failed to choose config with EGL_SWAP_BEHAVIOR_PRESERVED, retrying without...
2020-11-20 23:31:47.265 1993-2017/com.example.eventcountdown D/eglCodecCommon: setVertexArrayObject: set vao to 0 (0) 0 0
2020-11-20 23:31:47.265 1993-2017/com.example.eventcountdown D/EGL_emulation: eglCreateContext: 0xedc7fdc0: maj 3 min 0 rcv 3
2020-11-20 23:31:47.279 1993-2017/com.example.eventcountdown D/EGL_emulation: eglMakeCurrent: 0xedc7fdc0: ver 3 0 (tinfo 0xe2b4ac40)
2020-11-20 23:31:47.346 1993-2017/com.example.eventcountdown W/Gralloc3: mapper 3.x is not supported
2020-11-20 23:31:47.354 1993-2017/com.example.eventcountdown D/HostConnection: createUnique: call
2020-11-20 23:31:47.355 1993-2017/com.example.eventcountdown D/HostConnection: HostConnection::get() New Host Connection established 0xd7851710, tid 2017
2020-11-20 23:31:47.390 1993-2017/com.example.eventcountdown 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_YUV420_888_to_NV21 ANDROID_EMU_YUV_Cache ANDROID_EMU_async_unmap_buffer ANDROID_EMU_vulkan_free_memory_sync ANDROID_EMU_vulkan_shader_float16_int8 ANDROID_EMU_vulkan_async_queue_submit GL_OES_EGL_image_external_essl3 GL_OES_vertex_array_object GL_KHR_texture_compression_astc_ldr ANDROID_EMU_gles_max_version_3_0 
2020-11-20 23:31:47.391 1993-2017/com.example.eventcountdown D/eglCodecCommon: allocate: Ask for block of size 0x1000
2020-11-20 23:31:47.397 1993-2017/com.example.eventcountdown D/eglCodecCommon: allocate: ioctl allocate returned offset 0x3ffff2000 size 0x2000
2020-11-20 23:31:47.495 1993-2017/com.example.eventcountdown D/EGL_emulation: eglMakeCurrent: 0xedc7fdc0: ver 3 0 (tinfo 0xe2b4ac40)
2020-11-20 23:31:47.501 1993-2017/com.example.eventcountdown D/eglCodecCommon: setVertexArrayObject: set vao to 0 (0) 1 0
2020-11-20 23:31:48.096 1993-2004/com.example.eventcountdown I/.eventcountdow: Background young concurrent copying GC freed 3484(960KB) AllocSpace objects, 1(20KB) LOS objects, 81% free, 1355KB/7499KB, paused 649us total 214.184ms
2020-11-20 23:31:48.331 1993-1993/com.example.eventcountdown I/Choreographer: Skipped 68 frames!  The application may be doing too much work on its main thread.
2020-11-20 23:31:54.032 1993-1993/com.example.eventcountdown W/ActivityThread: handleWindowVisibility: no activity for token android.os.BinderProxy@e1c1488
2020-11-20 23:31:54.408 1993-1993/com.example.eventcountdown D/AndroidRuntime: Shutting down VM
2020-11-20 23:31:54.415 1993-1993/com.example.eventcountdown E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.eventcountdown, PID: 1993
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.eventcountdown/com.example.eventcountdown.EventDetails}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase com.example.eventcountdown.eventDbHelper.getWritableDatabase()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
        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$H.handleMessage(ActivityThread.java:2016)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase com.example.eventcountdown.eventDbHelper.getWritableDatabase()' on a null object reference
        at com.example.eventcountdown.EventDetails.onCreate(EventDetails.java:36)
        at android.app.Activity.performCreate(Activity.java:7802)
        at android.app.Activity.performCreate(Activity.java:7791)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409) 
        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$H.handleMessage(ActivityThread.java:2016) 
        at android.os.Handler.dispatchMessage(Handler.java:107) 
        at android.os.Looper.loop(Looper.java:214) 
        at android.app.ActivityThread.main(ActivityThread.java:7356) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) 
2020-11-20 23:31:54.440 1993-1993/com.example.eventcountdown I/Process: Sending signal. PID: 1993 SIG: 9

MainActivity.java

public class MainActivity extends androidx.appcompat.app.AppCompatActivity {
    private static final String TAG = "MainActivity";
    private eventDbHelper mHelper;
    private ListView mEventListView;
    private ArrayAdapter<String> mAdapter;
    private DatePickerDialog.OnDateSetListener mDateSetListener;
    EditText event;
    TextView date, time;


    public interface DateDialogListener {
        void onFinishDialog(Date date);
    }


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

        mHelper = new eventDbHelper(this);
        mEventListView = (ListView) findViewById(R.id.events);


        updateUI();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main_menu, menu);
        return super.onCreateOptionsMenu(menu);
    }


    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.action_add_event:
                Intent intent = new Intent(getApplicationContext(), EventDetails.class);
                startActivity(intent);

                String title = getIntent().getStringExtra("EVENT_TITLE");
                String date = getIntent().getStringExtra("EVENT_DATE");
                String time = getIntent().getStringExtra("EVENT_TIME");
                updateUI();
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }

    public void deleteEvent(View view) {
        View parent = (View) view.getParent();
        TextView eventTextView = (TextView) parent.findViewById(R.id.event_title);
        String event = String.valueOf(eventTextView.getText());
        SQLiteDatabase db = mHelper.getWritableDatabase();
        db.delete(eventContract.EventEntry.TABLE,
                eventContract.EventEntry.COL_EVENT_TITLE + " = ?",
                new String[]{event});
        db.close();
        updateUI();
    }

    private void updateUI() {
        ArrayList<String> eventList = new ArrayList<>();
        SQLiteDatabase db = mHelper.getReadableDatabase();
        Cursor cursor = db.query(eventContract.EventEntry.TABLE,
                new String[]{eventContract.EventEntry._ID, eventContract.EventEntry.COL_EVENT_TITLE},
                null, null, null, null, null);
        while (cursor.moveToNext()) {
            int idx = cursor.getColumnIndex(eventContract.EventEntry.COL_EVENT_TITLE);
            eventList.add(cursor.getString(idx));
        }

        if (mAdapter == null) {
            mAdapter = new ArrayAdapter<>(this,
                    R.layout.new_event,
                    R.id.event_title,
                    eventList);
            mEventListView.setAdapter(mAdapter);
        } else {
            mAdapter.clear();
            mAdapter.addAll(eventList);
            mAdapter.notifyDataSetChanged();
        }

        cursor.close();
        db.close();
    }
}

activity_main.xml

<?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:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="10dp"
    android:gravity="center_horizontal"
    tools:context=".MainActivity">

    <ListView
        android:id="@+id/events"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</RelativeLayout>

EventDetails.java

public class EventDetails extends AppCompatActivity {
    private eventDbHelper mHelper;
    EditText event;
    TextView date, time;
    Button done, cancel;
    //mHelper = new eventDbHelper(this);

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

        event = (EditText) findViewById(R.id.event_title);
        date = (TextView) findViewById(R.id.event_date);
        time = (TextView) findViewById(R.id.event_time);
        done = (Button) findViewById(R.id.Done);
        cancel = (Button) findViewById(R.id.Cancel);

        SQLiteDatabase db = mHelper.getWritableDatabase();
        ContentValues eTitle = new ContentValues();
        ContentValues eDate = new ContentValues();
        ContentValues eTime = new ContentValues();


        done.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String e = String.valueOf(event.getText());
                SimpleDateFormat sdf = new SimpleDateFormat("dd-MM-yyyy");
                String d = sdf.format(new Date());
                String t = String.valueOf(time.getText());

                eTitle.put(eventContract.EventEntry.COL_EVENT_TITLE, e);
                eDate.put(eventContract.EventEntry.COL_EVENT_DATE, d);
                eTime.put(eventContract.EventEntry.COL_EVENT_TIME, t);
                db.insertWithOnConflict(eventContract.EventEntry.TABLE,
                        null,
                        eTitle,
                        SQLiteDatabase.CONFLICT_REPLACE);
                Intent intent = new Intent(getBaseContext(), MainActivity.class);
                intent.putExtra("EVENT_TITLE", e);
                intent.putExtra("EVENT_DATE", d);
                intent.putExtra("EVENT_TIME", t);
                startActivity(intent);
            }
        });

        cancel.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Toast.makeText(EventDetails.this, "Event Cancelled!", Toast.LENGTH_SHORT).show();
                Intent intent  = new Intent(getApplicationContext(), MainActivity.class);
            }
        });
    }
}

activity_event_details.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_gravity="center_vertical"
    android:orientation="vertical"
    android:padding="10dp"
    android:gravity="center_horizontal"
    tools:context=".EventDetails">


    <TextView
        android:id="@+id/pageTitle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_alignParentLeft="false"
        android:layout_centerHorizontal="true"
        android:layout_marginStart="130dp"
        android:layout_marginLeft="130dp"
        android:layout_marginTop="10dp"
        android:layout_marginEnd="10dp"
        android:layout_marginBottom="10dp"
        android:hint="Enter Event Details"
        android:inputType="text"
        android:textColor="#000000"
        android:textSize="30sp" />

    <EditText
        android:id="@+id/event_title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/pageTitle"
        android:layout_alignParentStart="true"
        android:layout_alignParentLeft="true"
        android:layout_marginStart="20dp"
        android:layout_marginLeft="20dp"
        android:layout_marginTop="57dp"
        android:layout_marginEnd="10dp"
        android:layout_marginBottom="10dp"
        android:hint="Event Title"
        android:inputType="text"
        android:textSize="20sp" />

    <TextView
        android:id="@+id/event_date"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/event_title"
        android:layout_alignParentStart="true"
        android:layout_alignParentLeft="true"
        android:layout_marginStart="22dp"
        android:layout_marginLeft="22dp"
        android:layout_marginTop="80dp"
        android:layout_marginEnd="10dp"
        android:layout_marginBottom="10dp"
        android:hint="Date"
        android:inputType="text"
        android:textSize="20sp" />

    <TextView
        android:id="@+id/event_time"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/event_date"
        android:layout_alignParentStart="true"
        android:layout_alignParentLeft="true"
        android:layout_marginStart="22dp"
        android:layout_marginLeft="22dp"
        android:layout_marginTop="59dp"
        android:layout_marginEnd="10dp"
        android:layout_marginBottom="10dp"
        android:hint="Time"
        android:inputType="text"
        android:textSize="20sp" />

    <Button
        android:id="@+id/Done"
        android:layout_width="511dp"
        android:layout_height="wrap_content"

        android:layout_alignWithParentIfMissing="true"
        android:layout_below="@+id/event_time"
        android:layout_marginTop="30dp"
        android:layout_marginBottom="5dp"
        android:text="Done" />

    <Button
        android:id="@+id/Cancel"
        android:layout_width="511dp"
        android:layout_height="wrap_content"

        android:layout_alignWithParentIfMissing="true"
        android:layout_below="@+id/Done"

        android:layout_marginTop="30dp"
        android:layout_marginBottom="5dp"
        android:text="Cancel" />

</RelativeLayout>

eventDbHelper.java

public class eventDbHelper extends SQLiteOpenHelper {


    public eventDbHelper(Context context) {
        super(context, eventContract.DB_NAME, null, eventContract.DB_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase myDB) {
        String createTable = "CREATE TABLE " + eventContract.EventEntry.TABLE + " ( " +
                eventContract.EventEntry._ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
                eventContract.EventEntry.COL_EVENT_TITLE + " TEXT NOT NULL," +
                eventContract.EventEntry.COL_EVENT_DATE + " TEXT NOT NULL," +
                eventContract.EventEntry.COL_EVENT_TIME  +  " TEXT NOT NULL);";

        myDB.execSQL(createTable);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + eventContract.EventEntry.TABLE);
        onCreate(db);
    }
}

eventContract.java

public class eventContract {
    public static final String DB_NAME = "event.db";
    public static final int DB_VERSION = 1;

    public class EventEntry implements BaseColumns {
        public static final String TABLE = "events";

        public static final String COL_EVENT_TITLE = "title";
        public static final String COL_EVENT_DATE = "date";
        public static final String COL_EVENT_TIME = "time";
    }
}

ma​​in_menu.xml

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <item
        android:id="@+id/action_add_event"
        android:icon="@android:drawable/ic_menu_add"
        android:title="Add Event"
        app:showAsAction="always" />
</menu>

【问题讨论】：

  • 在 EventDetails 活动的 onCreate() 方法中，在 SQLiteDatabase db = mHelper.getWritableDatabase(); 之前添加 mHelper = new eventDbHelper(this);。
  • 有效！！！谢谢你：）

标签： java android sqlite android-studio


【解决方案1】：

在 java 中，类的每个实例都必须调用构造函数（实例化）才能成为对象。安卓使用java。
这意味着您最具体的活动com.example.eventcountdown.EventDetails 必须由 Android 系统在内部实例化。这绝对意味着当您在//mHelper = new eventDbHelper(this); 取消注释实例化时，请注意this 的使用可能是不安全的，因为内部活动配置尚未对实例完成。
这表明我们应该在我们最确定自己安全的地方做同样的事情。这肯定是在onCreate 方法中。但是你没有这样做。尝试从空对象mHelper 调用时导致NullPointerException。从OnCreate 传播异常以形成您看到的日志。你需要初始化

mHelper = new eventDbHelper(this)


在onCreate里面避免这样的错误。

【讨论】：

    【解决方案2】：

    mHelper 未初始化，因此应用程序崩溃。您必须对其进行初始化以防止这种情况发生。

    在 onCreate() 方法中试试这个：

    eventDbHelper mHelper = new eventDbHelper(this);

    【讨论】：

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