我几个月来一直在创建和测试一个应用。它的一部分是将应用程序从Android Studio运行到模拟器，并且一切正常。但是，当我尝试直接从连接的设备安装或运行该应用时，该应用崩溃了片刻，并且没有任何有关错误或任何消息的消息框。
这是logcat：
java.lang.RuntimeException: Unable to start activity ComponentInfo{thrill.ma.mathrill/thrill.ma.mathrill.Home}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3318)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3429)
at android.app.ActivityThread.-wrap12(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2009)
at android.os.Handler.dispatchMessage(Handler.java:109)
at android.os.Looper.loop(Looper.java:166)
at android.app.ActivityThread.main(ActivityThread.java:7555)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:469)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:963)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at thrill.ma.mathrill.Home.onCreate(Home.java:37)
at android.app.Activity.performCreate(Activity.java:7343)
at android.app.Activity.performCreate(Activity.java:7333)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1219)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3271)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3429)
at android.app.ActivityThread.-wrap12(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2009)
at android.os.Handler.dispatchMessage(Handler.java:109)
at android.os.Looper.loop(Looper.java:166)
at android.app.ActivityThread.main(ActivityThread.java:7555)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:469)
这是我的home.java。
public class Home extends AppCompatActivity implements View.OnClickListener {
DatabaseHelper db;
Helpers h = new Helpers();
Data data = new Data();
Button btnLessons, btnPVP, btnProgress;
String username = "";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.home);
db = new DatabaseHelper(this);
//data.data(db);
//db.InsertUserTest("Test");
h.fullscreen(getWindow().getDecorView());
try{
username = getIntent().getExtras().getString("Username");
} catch(Exception e) {
username = "";
}
btnLessons = findViewById(R.id.btnLessons);
btnPVP = findViewById(R.id.btnPVP);
btnProgress = findViewById(R.id.btnProgress);
btnLessons.setOnClickListener(this);
btnPVP.setOnClickListener(this);
btnProgress.setOnClickListener(this);
}
@Override
public void onClick(View v) {
Intent intent = new Intent();
switch(v.getId()) {
case R.id.btnLessons:
if(username.equals("")) intent = new Intent(this, Login.class);
else intent = new Intent(this, LessonsMain.class);
break;
case R.id.btnPVP:
intent = new Intent(this, PVP.class);
break;
case R.id.btnProgress:
intent = new Intent(this, Quiz.class);
break;
}
intent.putExtra("Username", "" + username);
startActivity(intent);
}
}
I would really appreciate your help. Thank you.
这是首页布局：
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:weightSum="100">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="25"
android:gravity="center"
android:orientation="horizontal">
<ImageView
android:layout_width="600dp"
android:layout_height="120dp"
app:srcCompat="@drawable/title" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="80"
android:gravity="left|center"
android:orientation="horizontal">
<LinearLayout
android:layout_width="300dp"
android:layout_height="match_parent"
android:gravity="center"
android:orientation="vertical">
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="55dp"
android:gravity="center"
android:orientation="horizontal">
<Button
android:id="@+id/btnLessons"
android:layout_width="wrap_content"
android:layout_height="70dp"
android:background="@drawable/button_lessons" />
</LinearLayout>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="55dp"
android:gravity="center"
android:orientation="horizontal">
<Button
android:id="@+id/btnPVP"
android:layout_width="wrap_content"
android:layout_height="70dp"
android:background="@drawable/button_pvp" />
</LinearLayout>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="55dp"
android:gravity="center"
android:orientation="horizontal">
<Button
android:id="@+id/btnProgress"
android:layout_width="wrap_content"
android:layout_height="70dp"
android:background="@drawable/button_progress" />
</LinearLayout>
</LinearLayout>
<LinearLayout
android:layout_width="341dp"
android:layout_height="match_parent"
android:orientation="horizontal">
<LinearLayout
android:layout_width="190dp"
android:layout_height="match_parent"
android:orientation="horizontal"></LinearLayout>
<LinearLayout
android:layout_width="100dp"
android:layout_height="match_parent"
android:gravity="bottom|right|center"
android:orientation="vertical"
android:paddingBottom="30dp">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="80dp"
android:gravity="center"
android:orientation="horizontal">
<Button
android:layout_width="80dp"
android:layout_height="80dp"
android:background="@drawable/button_developer" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="80dp"
android:gravity="center"
android:orientation="horizontal">
<Button
android:layout_width="80dp"
android:layout_height="80dp"
android:background="@drawable/button_settings" />
</LinearLayout>
</LinearLayout>
</LinearLayout>
</LinearLayout>
</LinearLayout>