当我切换到包含片段的活动时，应用程序崩溃(二进制XML文件行#10:Binary XML文件行#10:膨胀类片段时出错)

Question

当我按下按钮打开另一个包含片段的活动时，我的应用程序崩溃。我是安卓工作室的新手，似乎找不到任何解决方案。

在activity_main.xml中，我删除了这个问题的其他按钮，因为我想主要关注这个monday_btn。

我研究了这种类型的错误，并尝试了许多技巧，但似乎都不起作用。

主要活动.java

package com.example.dietmanagement;
import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.FragmentTransaction;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
/*Intent i = getIntent();
String current_user = i.getStringExtra("current_user");
TextView current_user_txtview = findViewById(R.id.current_user);
current_user_txtview.setText("Welcome, " + current_user);*/
Button monday = findViewById(R.id.monday_btn);
monday.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent day = new Intent(MainActivity.this, DayActivity.class);
startActivity(day);
}
});
}
}

DayActivity.java

package com.example.dietmanagement;
import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.FragmentTransaction;
import android.content.Intent;
import android.os.Bundle;
public class DayActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_day);
FragmentTransaction fragmentTransaction;
fragmentTransaction = getSupportFragmentManager().beginTransaction();
DayFragment dayFragment = new DayFragment();
fragmentTransaction.add(R.id.dayfragment, dayFragment);
fragmentTransaction.commit();

}
}

DayFragment.java

package com.example.dietmanagement;
import android.os.Bundle;
import androidx.fragment.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class DayFragment extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view =  inflater.inflate(R.layout.fragment_day, container, false);
return view;
}
}

fragment_day.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout 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/background_green"
tools:context=".DayFragment">

<TextView
android:id="@+id/day"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="24dp"
android:text="@string/day" />
</FrameLayout>

activity_day.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:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/background_green"
tools:context=".DayActivity">
<fragment
android:id="@+id/dayfragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent">
</fragment>

</androidx.constraintlayout.widget.ConstraintLayout>

activity_main.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:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/background_green"
tools:context=".MainActivity">
<Button
android:id="@+id/monday_btn"
android:layout_width="140dp"
android:layout_height="86dp"
android:text="@string/monday"
android:textColor="#6FED84"
android:textSize="16sp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.091"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/main_title"
app:layout_constraintVertical_bias="0.082" />
</androidx.constraintlayout.widget.ConstraintLayout>

这是我收到的错误消息：

2021-03-21 23:34:35.459 29479-29479/com.example.dietmanagement E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.dietmanagement, PID: 29479
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.dietmanagement/com.example.dietmanagement.DayActivity}: android.view.InflateException: Binary XML file line #10: Binary XML file line #10: Error inflating class fragment
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
Caused by: android.view.InflateException: Binary XML file line #10: Binary XML file line #10: Error inflating class fragment
Caused by: android.view.InflateException: Binary XML file line #10: Error inflating class fragment
Caused by: java.lang.NullPointerException
at java.lang.VMClassLoader.findLoadedClass(Native Method)
at java.lang.ClassLoader.findLoadedClass(ClassLoader.java:738)
at java.lang.ClassLoader.loadClass(ClassLoader.java:363)
at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
at android.app.Fragment.instantiate(Fragment.java:617)
at android.app.FragmentContainer.instantiate(FragmentContainer.java:49)
at android.app.FragmentManagerImpl.onCreateView(FragmentManager.java:3602)
at android.app.FragmentController.onCreateView(FragmentController.java:98)
at android.app.Activity.onCreateView(Activity.java:6187)
at androidx.fragment.app.FragmentActivity.onCreateView(FragmentActivity.java:338)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:780)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:730)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:863)
at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:824)
at android.view.LayoutInflater.inflate(LayoutInflater.java:515)
at android.view.LayoutInflater.inflate(LayoutInflater.java:423)
at android.view.LayoutInflater.inflate(LayoutInflater.java:374)
at androidx.appcompat.app.AppCompatDelegateImpl.setContentView(AppCompatDelegateImpl.java:696)
at androidx.appcompat.app.AppCompatActivity.setContentView(AppCompatActivity.java:170)
at com.example.dietmanagement.DayActivity.onCreate(DayActivity.java:16)
at android.app.Activity.performCreate(Activity.java:6975)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

Answer 1

您试图以两种不同的方式加载片段-直接通过带有<fragment>标记的布局，这需要您指定实际要加载的片段，以及作为活动中的事务，该事务需要放置片段的布局。

// This says - "hey Android load up a fragment for me", but you don't say which
<fragment
android:id="@+id/dayfragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent">
</fragment>

但是。。。

// This says - "hey Android, shove the new "dayFragment" into the view R.id.dayFragment".
// But based on your previous XML declaration, R.id.dayFragment is itself already a
// Fragment!
FragmentTransaction fragmentTransaction;
fragmentTransaction = getSupportFragmentManager().beginTransaction();
DayFragment dayFragment = new DayFragment();
fragmentTransaction.add(R.id.dayfragment, dayFragment);
fragmentTransaction.commit();

根据您发布的内容，最简单的解决方案是用FragmentContainerView替换<fragment>元素，并将代码留在活动中或在xml中声明类。请参阅文档中有关如何以两种方式实现这一点的示例。

Answer 2

您的<fragment>元素没有说明它应该加载什么片段。您需要在<fragment>中添加一个android:name，其中android:name的值是片段的完全限定类名：

<fragment
android:id="@+id/dayfragment"
android:name="com.example.dietmanagement.DayActivity"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent">
</fragment>