Android 和内存泄漏
Android and memory leaks
我担心从 leak canary 返回的信息。它显示在 UI 上声明的所有变量，例如片段中的 material 按钮、material 卡片视图、文本视图、图像视图等都导致内存泄漏。我不确定为什么会这样。
例如，leak canary 会在 Material 按钮中发现 1 个内存泄漏。当我在修复它的 onDestroyView() 中声明 material 按钮为 null 时。但是然后泄漏金丝雀将带来下一个 UI 变量，我实际上必须在 onDestroyView() 中将 UI 中的每个变量声明为 null 以阻止该片段泄漏。
当然，在 ondestroyView() 方法中必须将所有声明的变量都清空是不正常的做法，那样会很麻烦。我虽然 android 会在我们导航到新片段时处理这些事情。
private Window mWindow;
private Toolbar mToolbar;
private FloatingActionButton btnBack, btnNext;
private Button btnStart;
private TextView tvSetUpNotifications, tvTitle, tvDescription;
private ImageView ivToolbar;
private CardView cvNotification;
private Bundle args = new Bundle();
private NavController mNavController;
private View view;
@Override
public void onAttach(@NonNull Context context) {
super.onAttach(context);
((BaseApplication) getActivity().getApplication()).getAppComponent().inject(this);
}
public WorkoutCheckInIntro() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
view = inflater.inflate(R.layout.fragment_workout_checkin_intro, container, false);
// configure the Window variable to enable the colour to be set
mWindow = getActivity().getWindow();
mWindow.clearFlags(WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS);
mWindow.addFlags(WindowManager.LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
mWindow.setStatusBarColor(ContextCompat.getColor(getActivity(), R.color.calm));
return view;
}
@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
// Instantiate the Navigation Controller.
mNavController = Navigation.findNavController(view);
// Configure the bottom navbar
BottomNavigationView navBar = getActivity().findViewById(R.id.bottom_navigation);
navBar.setVisibility(View.VISIBLE);
// Method calls
assignVariables();
setOnClickListeners();
}
/**
* Method which assigns variables to elements in the XML file.
*/
private void assignVariables() {
// Initialising variables from the xml file.
btnStart = view.findViewById(R.id.checkInDailyButtonStart);
tvSetUpNotifications = view.findViewById(R.id.setUpNotificationsTextView);
cvNotification = view.findViewById(R.id.notification_cardView2);
// Configure the top toolbar
mToolbar = view.findViewById(R.id.toolbar_check_in_intro);
btnBack = mToolbar.findViewById(R.id.toolbar_back_button);
btnNext = mToolbar.findViewById(R.id.toolbar_next_button);
btnNext.hide();
tvTitle = mToolbar.findViewById(R.id.toolbar_workout_title);
tvTitle.setVisibility(View.VISIBLE);
tvTitle.setTextColor(ContextCompat.getColor(getActivity(), R.color.white));
tvTitle.setText(getString(R.string.check_in));
tvDescription = mToolbar.findViewById(R.id.toolbar_workout_description);
tvDescription.setVisibility(View.GONE);
tvDescription.setTextColor(ContextCompat.getColor(getContext(), R.color.white));
ivToolbar = mToolbar.findViewById(R.id.toolbar_workout_background);
ivToolbar.setVisibility(View.VISIBLE);
ivToolbar.setImageResource(R.drawable.check_in_intro);
}
/**
* Method which sets onClickListeners to buttons
*/
private void setOnClickListeners() {
btnStart.setOnClickListener(this);
btnBack.setOnClickListener(this);
tvSetUpNotifications.setOnClickListener(this);
cvNotification.setOnClickListener(this);
}
@Override
public void onClick(View view) {
switch (view.getId()) {
case R.id.toolbar_back_button:
if (mNavController.getCurrentDestination().getId() == R.id.workoutCheckInIntro) {
mNavController.navigate(R.id.action_workoutCheckInIntro_to_workoutFragment);
}
break;
case R.id.checkInDailyButtonStart:
// Boolean used in the WorkoutCheckInDailyMood.Class so when the user clicks
// the back button it will return them to this activity.
args.putBoolean(WORKOUT_CHECKIN_DAILY_MOOD, true);
if (mNavController.getCurrentDestination().getId() == R.id.workoutCheckInIntro) {
mNavController.navigate(R.id.action_workoutCheckInIntro_to_workoutMood, args);
}
break;
case R.id.notification_cardView2:
// Boolean used in the NotificationsSetUp.Class so when the user clicks
// the back button it will return them to this activity.
args.putBoolean(RETURN_TO_CHECKIN_WORKOUT, true);
if (mNavController.getCurrentDestination().getId() == R.id.workoutCheckInIntro) {
mNavController.navigate(R.id.action_workoutCheckInIntro_to_notificationsSetUp, args);
}
break;
}
}
@Override
public void onDestroyView() {
super.onDestroyView();
mToolbar = null;
view = null;
btnBack = null;
btnNext = null;
tvDescription = null;
tvTitle = null;
ivToolbar = null;
btnStart = null;
cvNotification = null;
tvSetUpNotifications = null;
}
}
<?xml version="1.0" encoding="utf-8"?>
<androidx.core.widget.NestedScrollView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="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="@color/white"
android:fillViewport="true"
tools:context=".ui.workouts.checkin.WorkoutCheckInIntro">
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent">
<include
android:id="@+id/toolbar_check_in_intro"
layout="@layout/toolbar_workout"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<TextView
android:id="@+id/textView"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="20dp"
android:layout_marginTop="16dp"
android:layout_marginEnd="20dp"
android:text="Workout Length"
android:textSize="@dimen/text_size_heading_16sp"
android:textStyle="bold"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/toolbar_check_in_intro" />
<TextView
android:id="@+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="20dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="20dp"
android:text="3 MIN - 5 MIN"
android:textSize="@dimen/text_size_timer"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/textView" />
<TextView
android:id="@+id/textView3"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="20dp"
android:layout_marginTop="24dp"
android:layout_marginEnd="20dp"
android:lineSpacingExtra="5sp"
android:text="We recommend to do this workout daily to develop a habit to check in with yourself each day. This is helpful as many of us are so busy that we become disconnected from our own thoughts and emotions."
android:textSize="@dimen/text_size_normal"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/textView2" />
<com.google.android.material.button.MaterialButton
android:id="@+id/checkInDailyButtonStart"
style="@style/btnStyleRed"
android:layout_width="0dp"
android:layout_marginStart="16dp"
android:layout_marginTop="32dp"
android:layout_marginEnd="16dp"
android:layout_marginBottom="8dp"
android:text="Start"
app:icon="@drawable/ic_dumb_bell_white_16dp"
app:iconGravity="textStart"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="1.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/notification_cardView2"
app:layout_constraintVertical_bias="1.0"
/>
<com.google.android.material.card.MaterialCardView
android:id="@+id/notification_cardView2"
android:layout_width="0dp"
android:layout_height="200dp"
android:layout_marginStart="32dp"
android:layout_marginTop="32dp"
android:layout_marginEnd="32dp"
android:clickable="true"
app:cardCornerRadius="10dp"
app:cardElevation="10dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/textView3">
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/setUpNotificationsTextView"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="32dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="32dp"
android:gravity="center"
android:text="Set up daily notifications to remind you to check-in"
android:textColor="@color/colorPrimary"
android:textSize="@dimen/text_size_normal"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<ImageView
android:id="@+id/appCompatImageView"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginStart="16dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="16dp"
android:layout_marginBottom="16dp"
android:adjustViewBounds="true"
app:srcCompat="@drawable/brain_insight"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/setUpNotificationsTextView" />
</androidx.constraintlayout.widget.ConstraintLayout>
</com.google.android.material.card.MaterialCardView>
</androidx.constraintlayout.widget.ConstraintLayout>
</androidx.core.widget.NestedScrollView>
───
│ GC Root: System class
│
├─ android.provider.FontsContract class
│ Leaking: NO (BaseApplication↓ is not leaking and a class is never leaking)
│ ↓ static FontsContract.sContext
├─ com.example.BaseApplication instance
│ Leaking: NO (WorkoutFragment↓ is not leaking and Application is a singleton)
│ ↓ BaseApplication.appComponent
├─ com.example.di.DaggerAppComponent instance
│ Leaking: NO (WorkoutFragment↓ is not leaking)
│ ↓ DaggerAppComponent.provideWorkoutAdapterProvider
├─ dagger.internal.DoubleCheck instance
│ Leaking: NO (WorkoutFragment↓ is not leaking)
│ ↓ DoubleCheck.instance
├─ com.example.adapters.RvAdapterWorkout instance
│ Leaking: NO (WorkoutFragment↓ is not leaking)
│ ↓ RvAdapterWorkout.mOnWorkoutListener
├─ com.example.ui.workouts.WorkoutFragment instance
│ Leaking: NO (WorkoutCheckInIntro↓ is not leaking and Fragment#mFragmentManager is not null)
│ ↓ WorkoutFragment.mFragmentManager
├─ androidx.fragment.app.FragmentManagerImpl instance
│ Leaking: NO (WorkoutCheckInIntro↓ is not leaking)
│ ↓ FragmentManagerImpl.mFragmentStore
├─ androidx.fragment.app.FragmentStore instance
│ Leaking: NO (WorkoutCheckInIntro↓ is not leaking)
│ ↓ FragmentStore.mActive
├─ java.util.HashMap instance
│ Leaking: NO (WorkoutCheckInIntro↓ is not leaking)
│ ↓ HashMap.table
├─ java.util.HashMap$Node[] array
│ Leaking: NO (WorkoutCheckInIntro↓ is not leaking)
│ ↓ HashMap$Node[].[3]
├─ java.util.HashMap$Node instance
│ Leaking: NO (WorkoutCheckInIntro↓ is not leaking)
│ ↓ HashMap$Node.value
├─ androidx.fragment.app.FragmentStateManager instance
│ Leaking: NO (WorkoutCheckInIntro↓ is not leaking)
│ ↓ FragmentStateManager.mFragment
├─ com.example.ui.workouts.checkin.WorkoutCheckInIntro instance
│ Leaking: NO (Fragment#mFragmentManager is not null)
│ ↓ WorkoutCheckInIntro.view
│ ~~~~
╰→ androidx.core.widget.NestedScrollView instance
Leaking: YES (ObjectWatcher was watching this because com.example.ui.workouts.checkin.WorkoutCheckInIntro received Fragment#onDestroyView() callback (references to its views should be cleared to prevent leaks))
key = 53dc4388-0db6-402a-9ee3-2db6617c98f5
watchDurationMillis = 192734
retainedDurationMillis = 187732
mContext instance of com.example.ui.main.MainActivity with mDestroyed = false
View#mParent is null
View#mAttachInfo is null (view detached)
View.mWindowAttachCount = 1
METADATA
Build.VERSION.SDK_INT: 30
Build.MANUFACTURER: Google
LeakCanary version: 2.4
App process name: com.
Analysis duration: 22667 ms
23 Leaks
┬───
│ GC Root: System class
│
├─ android.provider.FontsContract class
│ Leaking: NO (BaseApplication↓ is not leaking and a class is never leaking)
│ ↓ static FontsContract.sContext
├─ com.example.BaseApplication instance
│ Leaking: NO (Application is a singleton)
│ ↓ BaseApplication.appComponent
│ ~~~~~~~~~~~~
├─ com.example.di.DaggerAppComponent instance
│ Leaking: UNKNOWN
│ ↓ DaggerAppComponent.viewModelUsersProvider
│ ~~~~~~~~~~~~~~~~~~~~~~
├─ dagger.internal.DoubleCheck instance
│ Leaking: UNKNOWN
│ ↓ DoubleCheck.instance
│ ~~~~~~~~
╰→ com.example.persistence.viewmodel.ViewModelUsers instance
Leaking: YES (ObjectWatcher was watching this because com.example.persistence.viewmodel.ViewModelUsers received ViewModel#onCleared() callback)
key = 45b732d9-f6e0-4852-9b3c-8397c587f29f
watchDurationMillis = 223094
retainedDurationMillis = 218094
METADATA
Build.VERSION.SDK_INT: 30
Build.MANUFACTURER: Google
LeakCanary version: 2.4
App process name: com.
Analysis duration: 22667 ms
有一种比编写所有这些样板代码首先获取所有视图引用然后将它们设置为 null
更方便的方法
它被称为 view binding. You could as well use data binding，可让您更轻松地与视图数据进行交互。
不过是这样说的：
Note: Fragments outlive their views. Make sure you clean up any references to the binding class instance in the fragment's onDestroyView() method.
所以你仍然可以节省很多样板代码，在最坏的情况下只需要清除 一个 引用。
视图绑定（以及数据绑定），不同于findViewById，确保Null Safety and Type Safety。
在 Kotlin 中，您还有另一种选择。您可以使用 Kotlin 扩展（只是 gradle 文件中的另一个依赖项），并且您可以通过 ID 名称直接访问视图，而无需 findViewById。这种方法与 中的 view/data 绑定方法进行了比较。
我想再次指出 view/data 绑定可以在 Java 和 Kotlin 中使用。
这就是 android 试图使您的开发工作量最小化的方式。尤其是在许多片段之间移动时（以及所有片段中的 avoiding/reduce 样板代码）！
我担心从 leak canary 返回的信息。它显示在 UI 上声明的所有变量，例如片段中的 material 按钮、material 卡片视图、文本视图、图像视图等都导致内存泄漏。我不确定为什么会这样。
例如，leak canary 会在 Material 按钮中发现 1 个内存泄漏。当我在修复它的 onDestroyView() 中声明 material 按钮为 null 时。但是然后泄漏金丝雀将带来下一个 UI 变量，我实际上必须在 onDestroyView() 中将 UI 中的每个变量声明为 null 以阻止该片段泄漏。
当然，在 ondestroyView() 方法中必须将所有声明的变量都清空是不正常的做法，那样会很麻烦。我虽然 android 会在我们导航到新片段时处理这些事情。
private Window mWindow;
private Toolbar mToolbar;
private FloatingActionButton btnBack, btnNext;
private Button btnStart;
private TextView tvSetUpNotifications, tvTitle, tvDescription;
private ImageView ivToolbar;
private CardView cvNotification;
private Bundle args = new Bundle();
private NavController mNavController;
private View view;
@Override
public void onAttach(@NonNull Context context) {
super.onAttach(context);
((BaseApplication) getActivity().getApplication()).getAppComponent().inject(this);
}
public WorkoutCheckInIntro() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
view = inflater.inflate(R.layout.fragment_workout_checkin_intro, container, false);
// configure the Window variable to enable the colour to be set
mWindow = getActivity().getWindow();
mWindow.clearFlags(WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS);
mWindow.addFlags(WindowManager.LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
mWindow.setStatusBarColor(ContextCompat.getColor(getActivity(), R.color.calm));
return view;
}
@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
// Instantiate the Navigation Controller.
mNavController = Navigation.findNavController(view);
// Configure the bottom navbar
BottomNavigationView navBar = getActivity().findViewById(R.id.bottom_navigation);
navBar.setVisibility(View.VISIBLE);
// Method calls
assignVariables();
setOnClickListeners();
}
/**
* Method which assigns variables to elements in the XML file.
*/
private void assignVariables() {
// Initialising variables from the xml file.
btnStart = view.findViewById(R.id.checkInDailyButtonStart);
tvSetUpNotifications = view.findViewById(R.id.setUpNotificationsTextView);
cvNotification = view.findViewById(R.id.notification_cardView2);
// Configure the top toolbar
mToolbar = view.findViewById(R.id.toolbar_check_in_intro);
btnBack = mToolbar.findViewById(R.id.toolbar_back_button);
btnNext = mToolbar.findViewById(R.id.toolbar_next_button);
btnNext.hide();
tvTitle = mToolbar.findViewById(R.id.toolbar_workout_title);
tvTitle.setVisibility(View.VISIBLE);
tvTitle.setTextColor(ContextCompat.getColor(getActivity(), R.color.white));
tvTitle.setText(getString(R.string.check_in));
tvDescription = mToolbar.findViewById(R.id.toolbar_workout_description);
tvDescription.setVisibility(View.GONE);
tvDescription.setTextColor(ContextCompat.getColor(getContext(), R.color.white));
ivToolbar = mToolbar.findViewById(R.id.toolbar_workout_background);
ivToolbar.setVisibility(View.VISIBLE);
ivToolbar.setImageResource(R.drawable.check_in_intro);
}
/**
* Method which sets onClickListeners to buttons
*/
private void setOnClickListeners() {
btnStart.setOnClickListener(this);
btnBack.setOnClickListener(this);
tvSetUpNotifications.setOnClickListener(this);
cvNotification.setOnClickListener(this);
}
@Override
public void onClick(View view) {
switch (view.getId()) {
case R.id.toolbar_back_button:
if (mNavController.getCurrentDestination().getId() == R.id.workoutCheckInIntro) {
mNavController.navigate(R.id.action_workoutCheckInIntro_to_workoutFragment);
}
break;
case R.id.checkInDailyButtonStart:
// Boolean used in the WorkoutCheckInDailyMood.Class so when the user clicks
// the back button it will return them to this activity.
args.putBoolean(WORKOUT_CHECKIN_DAILY_MOOD, true);
if (mNavController.getCurrentDestination().getId() == R.id.workoutCheckInIntro) {
mNavController.navigate(R.id.action_workoutCheckInIntro_to_workoutMood, args);
}
break;
case R.id.notification_cardView2:
// Boolean used in the NotificationsSetUp.Class so when the user clicks
// the back button it will return them to this activity.
args.putBoolean(RETURN_TO_CHECKIN_WORKOUT, true);
if (mNavController.getCurrentDestination().getId() == R.id.workoutCheckInIntro) {
mNavController.navigate(R.id.action_workoutCheckInIntro_to_notificationsSetUp, args);
}
break;
}
}
@Override
public void onDestroyView() {
super.onDestroyView();
mToolbar = null;
view = null;
btnBack = null;
btnNext = null;
tvDescription = null;
tvTitle = null;
ivToolbar = null;
btnStart = null;
cvNotification = null;
tvSetUpNotifications = null;
}
}
<?xml version="1.0" encoding="utf-8"?>
<androidx.core.widget.NestedScrollView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="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="@color/white"
android:fillViewport="true"
tools:context=".ui.workouts.checkin.WorkoutCheckInIntro">
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent">
<include
android:id="@+id/toolbar_check_in_intro"
layout="@layout/toolbar_workout"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<TextView
android:id="@+id/textView"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="20dp"
android:layout_marginTop="16dp"
android:layout_marginEnd="20dp"
android:text="Workout Length"
android:textSize="@dimen/text_size_heading_16sp"
android:textStyle="bold"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/toolbar_check_in_intro" />
<TextView
android:id="@+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="20dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="20dp"
android:text="3 MIN - 5 MIN"
android:textSize="@dimen/text_size_timer"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/textView" />
<TextView
android:id="@+id/textView3"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="20dp"
android:layout_marginTop="24dp"
android:layout_marginEnd="20dp"
android:lineSpacingExtra="5sp"
android:text="We recommend to do this workout daily to develop a habit to check in with yourself each day. This is helpful as many of us are so busy that we become disconnected from our own thoughts and emotions."
android:textSize="@dimen/text_size_normal"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/textView2" />
<com.google.android.material.button.MaterialButton
android:id="@+id/checkInDailyButtonStart"
style="@style/btnStyleRed"
android:layout_width="0dp"
android:layout_marginStart="16dp"
android:layout_marginTop="32dp"
android:layout_marginEnd="16dp"
android:layout_marginBottom="8dp"
android:text="Start"
app:icon="@drawable/ic_dumb_bell_white_16dp"
app:iconGravity="textStart"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="1.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/notification_cardView2"
app:layout_constraintVertical_bias="1.0"
/>
<com.google.android.material.card.MaterialCardView
android:id="@+id/notification_cardView2"
android:layout_width="0dp"
android:layout_height="200dp"
android:layout_marginStart="32dp"
android:layout_marginTop="32dp"
android:layout_marginEnd="32dp"
android:clickable="true"
app:cardCornerRadius="10dp"
app:cardElevation="10dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/textView3">
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/setUpNotificationsTextView"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="32dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="32dp"
android:gravity="center"
android:text="Set up daily notifications to remind you to check-in"
android:textColor="@color/colorPrimary"
android:textSize="@dimen/text_size_normal"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<ImageView
android:id="@+id/appCompatImageView"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginStart="16dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="16dp"
android:layout_marginBottom="16dp"
android:adjustViewBounds="true"
app:srcCompat="@drawable/brain_insight"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/setUpNotificationsTextView" />
</androidx.constraintlayout.widget.ConstraintLayout>
</com.google.android.material.card.MaterialCardView>
</androidx.constraintlayout.widget.ConstraintLayout>
</androidx.core.widget.NestedScrollView>
───
│ GC Root: System class
│
├─ android.provider.FontsContract class
│ Leaking: NO (BaseApplication↓ is not leaking and a class is never leaking)
│ ↓ static FontsContract.sContext
├─ com.example.BaseApplication instance
│ Leaking: NO (WorkoutFragment↓ is not leaking and Application is a singleton)
│ ↓ BaseApplication.appComponent
├─ com.example.di.DaggerAppComponent instance
│ Leaking: NO (WorkoutFragment↓ is not leaking)
│ ↓ DaggerAppComponent.provideWorkoutAdapterProvider
├─ dagger.internal.DoubleCheck instance
│ Leaking: NO (WorkoutFragment↓ is not leaking)
│ ↓ DoubleCheck.instance
├─ com.example.adapters.RvAdapterWorkout instance
│ Leaking: NO (WorkoutFragment↓ is not leaking)
│ ↓ RvAdapterWorkout.mOnWorkoutListener
├─ com.example.ui.workouts.WorkoutFragment instance
│ Leaking: NO (WorkoutCheckInIntro↓ is not leaking and Fragment#mFragmentManager is not null)
│ ↓ WorkoutFragment.mFragmentManager
├─ androidx.fragment.app.FragmentManagerImpl instance
│ Leaking: NO (WorkoutCheckInIntro↓ is not leaking)
│ ↓ FragmentManagerImpl.mFragmentStore
├─ androidx.fragment.app.FragmentStore instance
│ Leaking: NO (WorkoutCheckInIntro↓ is not leaking)
│ ↓ FragmentStore.mActive
├─ java.util.HashMap instance
│ Leaking: NO (WorkoutCheckInIntro↓ is not leaking)
│ ↓ HashMap.table
├─ java.util.HashMap$Node[] array
│ Leaking: NO (WorkoutCheckInIntro↓ is not leaking)
│ ↓ HashMap$Node[].[3]
├─ java.util.HashMap$Node instance
│ Leaking: NO (WorkoutCheckInIntro↓ is not leaking)
│ ↓ HashMap$Node.value
├─ androidx.fragment.app.FragmentStateManager instance
│ Leaking: NO (WorkoutCheckInIntro↓ is not leaking)
│ ↓ FragmentStateManager.mFragment
├─ com.example.ui.workouts.checkin.WorkoutCheckInIntro instance
│ Leaking: NO (Fragment#mFragmentManager is not null)
│ ↓ WorkoutCheckInIntro.view
│ ~~~~
╰→ androidx.core.widget.NestedScrollView instance
Leaking: YES (ObjectWatcher was watching this because com.example.ui.workouts.checkin.WorkoutCheckInIntro received Fragment#onDestroyView() callback (references to its views should be cleared to prevent leaks))
key = 53dc4388-0db6-402a-9ee3-2db6617c98f5
watchDurationMillis = 192734
retainedDurationMillis = 187732
mContext instance of com.example.ui.main.MainActivity with mDestroyed = false
View#mParent is null
View#mAttachInfo is null (view detached)
View.mWindowAttachCount = 1
METADATA
Build.VERSION.SDK_INT: 30
Build.MANUFACTURER: Google
LeakCanary version: 2.4
App process name: com.
Analysis duration: 22667 ms
23 Leaks
┬───
│ GC Root: System class
│
├─ android.provider.FontsContract class
│ Leaking: NO (BaseApplication↓ is not leaking and a class is never leaking)
│ ↓ static FontsContract.sContext
├─ com.example.BaseApplication instance
│ Leaking: NO (Application is a singleton)
│ ↓ BaseApplication.appComponent
│ ~~~~~~~~~~~~
├─ com.example.di.DaggerAppComponent instance
│ Leaking: UNKNOWN
│ ↓ DaggerAppComponent.viewModelUsersProvider
│ ~~~~~~~~~~~~~~~~~~~~~~
├─ dagger.internal.DoubleCheck instance
│ Leaking: UNKNOWN
│ ↓ DoubleCheck.instance
│ ~~~~~~~~
╰→ com.example.persistence.viewmodel.ViewModelUsers instance
Leaking: YES (ObjectWatcher was watching this because com.example.persistence.viewmodel.ViewModelUsers received ViewModel#onCleared() callback)
key = 45b732d9-f6e0-4852-9b3c-8397c587f29f
watchDurationMillis = 223094
retainedDurationMillis = 218094
METADATA
Build.VERSION.SDK_INT: 30
Build.MANUFACTURER: Google
LeakCanary version: 2.4
App process name: com.
Analysis duration: 22667 ms
有一种比编写所有这些样板代码首先获取所有视图引用然后将它们设置为 null
它被称为 view binding. You could as well use data binding，可让您更轻松地与视图数据进行交互。
不过是这样说的：
Note: Fragments outlive their views. Make sure you clean up any references to the binding class instance in the fragment's
onDestroyView()method.
所以你仍然可以节省很多样板代码，在最坏的情况下只需要清除 一个 引用。
视图绑定（以及数据绑定），不同于findViewById，确保Null Safety and Type Safety。
在 Kotlin 中，您还有另一种选择。您可以使用 Kotlin 扩展（只是 gradle 文件中的另一个依赖项），并且您可以通过 ID 名称直接访问视图，而无需 findViewById。这种方法与