英文:
Why does adapter.add crash in android ListFragment
问题
我现在开始学习Android编程，但在一个ListFragment中遇到了问题。我在网上找到了一些关于相同问题的帖子，但是没有一个能够帮助我找到/理解我代码中的问题。
我创建了一个Android底部导航活动并修改了仪表板Fragment。目标是在列表中有一个按钮，当按钮被点击时，应该打开键盘，然后输入一个新的字符串并将其添加到列表中。在以下代码中，我尝试实现一个按钮，当点击它时，总是添加相同的字符串，因为我还在学习阶段，稍后会处理键盘部分。
代码总是能够编译通过，但当点击按钮并执行adapter.add命令时，应用程序会崩溃。当我在onCreateView中的setListAdapter之后直接添加adapter.add时，也会崩溃。
以下是我使用的文件：
DashboardFragment.java
package com.example.aktiehq.workout.ui.dashboard;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import androidx.fragment.app.ListFragment;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import com.example.aktiehq.workout.R;
import com.google.android.material.floatingactionbutton.FloatingActionButton;
public class DashboardFragment extends ListFragment {
String[] values = new String[] { "Message1", "Message2", "Message3" };
public ArrayAdapter<String> adapter;
public View onCreateView(@NonNull LayoutInflater inflater,
ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_dashboard, container,
false);
adapter = new ArrayAdapter<String>(getActivity(),
android.R.layout.simple_list_item_1, values);
setListAdapter(adapter);
FloatingActionButton button = rootView.findViewById(R.id.addListElement);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
adapter.add("test");
adapter.notifyDataSetChanged();
}
});
return rootView;
}
}
fragment_dashboard.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"
tools:context=".ui.dashboard.DashboardFragment">
<com.google.android.material.floatingactionbutton.FloatingActionButton
android:id="@+id/addListElement"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="16dp"
android:layout_marginBottom="64dp"
android:clickable="true"
android:src="@android:drawable/ic_input_add"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent" />
<ListView
android:id="@android:id/list"
android:layout_width="409dp"
android:layout_height="609dp"
tools:layout_editor_absoluteX="1dp"
tools:layout_editor_absoluteY="1dp" />
</androidx.constraintlayout.widget.ConstraintLayout>
点击按钮后的错误信息：
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.aktiehq.workout, PID: 18355
java.lang.UnsupportedOperationException
at java.util.AbstractList.add(AbstractList.java:404)
at java.util.AbstractList.add(AbstractList.java:425)
at android.widget.ArrayAdapter.add(ArrayAdapter.java:194)
at com.example.aktiehq.workout.ui.dashboard.DashboardFragment$1.onClick(DashboardFragment.java:45)
at android.view.View.performClick(View.java:5198)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
请问有人可以帮助我解释和修复这个问题吗？
非常感谢您的帮助，
Frank
<details>
<summary>英文:</summary>
I am starting to learn coding for android now and have a Problem in a ListFragment. I found threads with the same problem but none of them helped be finding / understanding the problem in my code.
I created an Android bottom navigation activity and modified the Dashboard Fragment. The Goal is to have a list with a button and when it is clicked a keyboard should open, a new string be entered and added to the list. In the following code I tried to implement a button that adds always the same string when it is clicked since I am still learning, I will work on the keyboard part later.
The code always compiles without problem but crashes when the button is clicked and the adapter.add command is executed. It also crashes when I add the adapter.add directly after the setListAdapter in onCreateView.
These are the files I use:
DashboardFragment.java
package com.example.aktiehq.workout.ui.dashboard;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.TextView;
import androidx.fragment.app.ListFragment;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;
import com.example.aktiehq.workout.R;
import com.google.android.material.floatingactionbutton.FloatingActionButton;
public class DashboardFragment extends ListFragment {
//private DashboardViewModel dashboardViewModel;
String[] values = new String[] { "Message1", "Message2", "Message3" };
public ArrayAdapter<String> adapter;
public View onCreateView(@NonNull LayoutInflater inflater,
ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_dashboard, container,
false);
adapter = new ArrayAdapter<String>(getActivity(),
android.R.layout.simple_list_item_1, values);
setListAdapter(adapter);
FloatingActionButton button = (FloatingActionButton) rootView.findViewById(R.id.addListElement);
//b.setOnClickListener((View.OnClickListener) this);
button.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View v)
{
adapter.add("test");
adapter.notifyDataSetChanged();
}
});
return rootView;
}
}
fragment_dashboard.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"
tools:context=".ui.dashboard.DashboardFragment">
<com.google.android.material.floatingactionbutton.FloatingActionButton
android:id="@+id/addListElement"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="16dp"
android:layout_marginBottom="64dp"
android:clickable="true"
android:src="@android:drawable/ic_input_add"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent" />
<ListView
android:id="@android:id/list"
android:layout_width="409dp"
android:layout_height="609dp"
tools:layout_editor_absoluteX="1dp"
tools:layout_editor_absoluteY="1dp" />
</androidx.constraintlayout.widget.ConstraintLayout>
Error when I click the button:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.aktiehq.workout, PID: 18355
java.lang.UnsupportedOperationException
at java.util.AbstractList.add(AbstractList.java:404)
at java.util.AbstractList.add(AbstractList.java:425)
at android.widget.ArrayAdapter.add(ArrayAdapter.java:194)
at com.example.aktiehq.workout.ui.dashboard.DashboardFragment$1.onClick(DashboardFragment.java:45)
at android.view.View.performClick(View.java:5198)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Can anyone please help me explaining and fixing the problem?
Thank you very much in advance,
Frank
</details>
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