java - 无法启动 Activity ComponentInfo

Question

当我运行我的 Activity registeration.java 或 login.java 时，它将 Intent 中的用户名传递给名为 profile.java 的新 Activity > 关于成功。问题是当我尝试登录时，应用程序崩溃并在 logcat 中给出以下错误。我尝试了有关此问题的 stackoverflow 问题上的所有内容，但没有一个解决它。任何建议都将受到高度赞赏。

FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.admin.funtube/com.example.admin.funtube.profile}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
            at android.app.ActivityThread.access$1500(ActivityThread.java:117)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:123)
            at android.app.ActivityThread.main(ActivityThread.java:3687)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:507)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:842)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.example.admin.funtube.profile.onCreate(profile.java:20)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
            at android.app.ActivityThread.access$1500(ActivityThread.java:117)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:123)
            at android.app.ActivityThread.main(ActivityThread.java:3687)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:507)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:842)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
            at dalvik.system.NativeStart.main(Native Method)

profile.java

public class profile extends AppCompatActivity {

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.profile);

        TextView welcometxt = (TextView) findViewById(R.id.welcome);

        Bundle extras = getIntent().getExtras();
        welcometxt.setText("Welcome " + extras.getString("name").toUpperCase());

    }
}

login.java

 if (email != null && password !=null) {
  String em=email.getText().toString();
  String pwd=password.getText().toString();
  String user=  FunTubeDBOperations.loginUsers(em, pwd);
  if(user!=null)
  {
  Toast.makeText(getApplicationContext(), "Login successfully!!", Toast.LENGTH_LONG).show();
   Intent intent = new Intent(login.this, profile.class);
   intent.putExtra("name", user);
   startActivity(intent);
   finish();
   }
   }

Profile.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">

    <ImageView
        android:id="@+id/header_imageview"
        android:layout_width="match_parent"
        android:layout_height="150dp"
        android:scaleType="centerCrop"
        android:src="@drawable/logo"
        android:adjustViewBounds="true"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true" />

    <LinearLayout
        android:id="@+id/informations_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        android:layout_below="@+id/header_imageview"
        android:gravity="center"
        android:paddingTop="32dp"
        android:paddingBottom="32dp">


        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textStyle="bold"
            android:textSize="17dp" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="4dp"
            android:gravity="center"
            android:textColor="#FF707070"/>

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="8dp"
            android:textColor="#FF909090" />

        <Button
            style="?android:attr/buttonStyleSmall"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="UploadPic"
            android:id="@+id/bup"
            android:layout_gravity="center_horizontal" />

    </LinearLayout>

    <HorizontalScrollView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:scrollbars="none"
        android:layout_below="@+id/informations_container"
        android:background="#FFF0F0F0">

        <LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal">



        </LinearLayout>
    </HorizontalScrollView>


    <ImageView
        android:layout_width="75dp"
        android:layout_height="75dp"
        android:src="@drawable/logo"
        android:layout_centerHorizontal="true"
        android:layout_above="@+id/informations_container"
        android:layout_marginBottom="-16dp" />

</RelativeLayout>

Answer 1

TextView welcometxt = (TextView) findViewById(R.id.welcome);

您的布局文件中没有名为 welcome 的小部件。因此，findViewById() 将无法检索它。因此，welcometxt 将为 null。