登錄方法有問題。我的活動包含片段容器和 2 個按鈕（登錄和注冊）。在活動的創(chuàng)建方法中，我初始化片段，并將登錄片段添加到容器中。在 onClickSignButtons 方法中，我有 switch case 函數(shù)，它應(yīng)該獲取按下的按鈕 id 并根據(jù)按鈕 id 進行一些思考。但點擊按鈕應(yīng)用程序崩潰。logcat 的日志如下：Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference at com.enjoyapp.eventmanagement.Screens.Login.View.LoginActivity.onClickSignButtons(LoginActivity.java:45)登錄活動public class LoginActivity extends AppCompatActivity implements LoginModel {private LoginPresenter presenter;private Fragment EmailAndPasswordFragment, userDetailsFragment;private Fragment selectedFragment = null;UserSingleton userSingleton;@Overrideprotected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_login); presenter = new LoginPresenter(this); EmailAndPasswordFragment = new EmailAndPasswordFieldsFragment(); userDetailsFragment = new UserDetailsFragment(); getSupportFragmentManager().beginTransaction().add(R.id.fields_container, new EmailAndPasswordFieldsFragment()) .commit(); selectedFragment = EmailAndPasswordFragment;}public void onClickSignButtons(View view) { switch (view.getId()) { case R.id.btnSignIn: if (selectedFragment == EmailAndPasswordFragment) { userSingleton.setmEmail(((EditText) EmailAndPasswordFragment.getView().findViewById(R.id.etEmail)).getText().toString().trim()); userSingleton.setmPassword(((EditText) EmailAndPasswordFragment.getView().findViewById(R.id.etPassword)).getText().toString().trim()); presenter.signIn(userSingleton.getmEmail(), userSingleton.getmPassword()); } else { getSupportFragmentManager().beginTransaction().add(R.id.fields_container, new EmailAndPasswordFieldsFragment()) .commit(); selectedFragment = EmailAndPasswordFragment;
4 回答
桃花長相依
TA貢獻1860條經(jīng)驗 獲得超8個贊
從我所看到的是，您正在初始化片段并將其存儲在變量 EmailAndPasswordFragment 中，但是在將片段添加到容器時，您再次重新初始化它。
這就是為什么它給出空指針異常。
這是你的onCreate
getSupportFragmentManager().beginTransaction().add(R.id.fields_container, EmailAndPasswordFragment) .commit();
慕的地6264312
TA貢獻1817條經(jīng)驗 獲得超6個贊
更新：哦天哪，我很抱歉大家，我只是忘記初始化 UserSingleton 類。
剛剛添加到 onCreate 方法的下一行： userSingleton = UserSingleton.getInstance();
xml 中有一個新代碼
public class LoginActivity extends AppCompatActivity implements LoginModel {
private LoginPresenter presenter;
private Fragment emailAndPasswordFragment;
private Fragment userDetailsFragment;
private Fragment selectedFragment = null;
UserSingleton userSingleton;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
presenter = new LoginPresenter(this);
emailAndPasswordFragment = new EmailAndPasswordFieldsFragment();
userDetailsFragment = new UserDetailsFragment();
getSupportFragmentManager().beginTransaction().add(R.id.fields_container, emailAndPasswordFragment)
.commit();
selectedFragment = emailAndPasswordFragment;
}
public void onClickSignInAndUpButtons(View view) {
switch (view.getId()) {
case R.id.btnSignIn:
if (selectedFragment == emailAndPasswordFragment) {
userSingleton.setmEmail(((EditText) emailAndPasswordFragment.getView().findViewById(R.id.etEmail)).getText().toString().trim());
userSingleton.setmPassword(((EditText) emailAndPasswordFragment.getView().findViewById(R.id.etPassword)).getText().toString().trim());
presenter.signIn(userSingleton.getmEmail(), userSingleton.getmPassword());
} else {
getSupportFragmentManager().beginTransaction().add(R.id.fields_container, emailAndPasswordFragment)
.commit();
selectedFragment = emailAndPasswordFragment;
}
break;
case R.id.btnGetStarted:
//TODO edd signup methos
break;
}
}
登錄活動 XML：
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:card_view="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:background="@drawable/gradien_color"
tools:context=".Screens.Login.View.LoginActivity">
<ImageView
android:id="@+id/logoMain"
android:layout_width="200dp"
android:layout_height="200dp"
android:layout_gravity="center"
android:layout_marginStart="8dp"
android:layout_marginTop="52dp"
android:layout_marginEnd="8dp"
android:contentDescription="@string/logo_main"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.497"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:srcCompat="@drawable/logo_main" />
<FrameLayout
android:id="@+id/fields_container"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:layout_marginBottom="8dp"
app:layout_constraintBottom_toTopOf="@+id/cvGetStarted"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/logoMain">
</FrameLayout>
<androidx.cardview.widget.CardView
android:id="@+id/cvGetStarted"
android:layout_width="300dp"
android:layout_height="50dp"
android:layout_marginStart="8dp"
android:layout_marginBottom="20dp"
android:translationZ="8dp"
app:layout_constraintBottom_toTopOf="@+id/btnSignIn"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.456"
app:layout_constraintStart_toStartOf="parent"
card_view:cardCornerRadius="25dp"
card_view:cardElevation="3dp">
<Button
android:id="@+id/btnGetStarted"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/register_button_style"
android:text="@string/btn_get_started"
android:textColor="@color/white" />
</androidx.cardview.widget.CardView>
<Button
android:id="@+id/btnSignIn"
android:layout_width="200dp"
android:layout_height="50dp"
android:layout_marginBottom="48dp"
android:background="@null"
android:onClick="onClickSignInAndUpButtons"
android:stateListAnimator="@null"
android:text="@string/btn_sign_in"
android:textColor="@color/white"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.497"
app:layout_constraintStart_toStartOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
片段類
public class EmailAndPasswordFieldsFragment extends Fragment {
private EditText etEmail, etPassword;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_email_and_password_fields, container, false);
etEmail = view.findViewById(R.id.etEmail);
etPassword = view.findViewById(R.id.etPassword);
return view;
}
}
片段 xml:
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:card_view="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".Screens.Login.View.UserDetailsFragment">
<LinearLayout
android:layout_width="350dp"
android:layout_height="150dp"
android:layout_gravity="center"
android:orientation="vertical"
android:gravity="center">
<androidx.cardview.widget.CardView
android:layout_width="250dp"
android:layout_height="40dp"
android:layout_marginStart="8dp"
android:layout_marginEnd="8dp"
android:layout_marginBottom="12dp"
android:translationZ="8dp"
card_view:cardBackgroundColor="@android:color/transparent"
card_view:cardCornerRadius="25dp"
card_view:cardElevation="3dp">
<EditText
android:id="@+id/etEmail"
android:layout_width="250dp"
android:layout_height="40dp"
android:background="@drawable/input_field_style"
android:drawableStart="@drawable/login_icon"
android:drawableTint="@color/tint_and_text_color"
android:ems="10"
android:hint="@string/hint_email"
android:inputType="textEmailAddress"
android:textColor="@color/main_text_color"
android:textColorHint="@color/tint_and_text_color"
android:textSize="16sp" />
</androidx.cardview.widget.CardView>
<androidx.cardview.widget.CardView
android:layout_width="250dp"
android:layout_height="40dp"
android:layout_marginStart="8dp"
android:layout_marginEnd="8dp"
android:layout_marginBottom="12dp"
android:translationZ="8dp"
card_view:cardBackgroundColor="@android:color/transparent"
card_view:cardCornerRadius="25dp"
card_view:cardElevation="3dp">
<EditText
android:id="@+id/etPassword"
android:layout_width="250dp"
android:layout_height="40dp"
android:background="@drawable/input_field_style"
android:drawableStart="@drawable/password_icon"
android:drawableTint="@color/tint_and_text_color"
android:ems="10"
android:hint="@string/hint_password"
android:inputType="textPassword"
android:textColor="@color/main_text_color"
android:textColorHint="@color/tint_and_text_color"
android:textSize="16sp" />
</androidx.cardview.widget.CardView>
</LinearLayout>
</FrameLayout>
慕姐4208626
TA貢獻1852條經(jīng)驗 獲得超7個贊
EmailAndPasswordFragment = new EmailAndPasswordFieldsFragment();
這是 EmailAndPasswordFragment 的第一個實例，在 add 方法中您將傳遞 EmailAndPasswordFragment 的新實例
在 onclick 內(nèi)部，您正在訪問第一個實例的值。
30秒到達戰(zhàn)場
TA貢獻1828條經(jīng)驗 獲得超6個贊
你的線路有問題
EmailAndPasswordFragment = new EmailAndPasswordFieldsFragment();
因為您正在創(chuàng)建 Fragment 對象，但將其分配給類名，而不是變量，然后您分配給selectedFragment由類名分配的變量。
解決辦法 更換線路
EmailAndPasswordFragment = new EmailAndPasswordFieldsFragment();
和
EmailAndPasswordFragment ePF = new EmailAndPasswordFieldsFragment();
和線
getSupportFragmentManager().beginTransaction().add(R.id.fields_container, new EmailAndPasswordFieldsFragment()) .commit(); selectedFragment = EmailAndPasswordFragment;
和
getSupportFragmentManager().beginTransaction().add(R.id.fields_container, ePF) .commit(); selectedFragment = ePF;
并將該行替換 if(selectedFragment == EmailAndPasswordFragment)為if(!(selectedFragment instanceof EmailAndPasswordFragment))
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