Android Kotlin中EditText搜索Firebase用户致RecyclerView崩溃

我在Android项目中采用EditText作为搜索框，结合Firebase Realtime Database实现用户搜索并将结果展示在RecyclerView中。使用addTextChangedListener()监听输入字符变化来触发搜索功能，但每次输入字母时应用都会崩溃。直接将所有用户数据加载到RecyclerView时，适配器工作正常。

相关代码 #

TextWatcher实现 #

searchBar.addTextChangedListener(object : TextWatcher{
            override fun beforeTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {
                TODO("Not yet implemented")
            }

            override fun onTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {
                searchUser(p0.toString().lowercase())
            }

            override fun afterTextChanged(p0: Editable?) {
                TODO("Not yet implemented")
            }
        })

搜索方法 #

private fun searchUser(s :String){
        val query = FirebaseDatabase.getInstance().getReference("Users").orderByChild("username")
        query.startAt(s)
        query.endAt(s+"\uf8ff")
        //Toast.makeText(requireContext(), "Search", Toast.LENGTH_SHORT).show()

        query.addValueEventListener(object : ValueEventListener {
            @SuppressLint("NotifyDataSetChanged")
            override fun onDataChange(snapshot: DataSnapshot) {
                userList.clear()
                for(theSnapshot in snapshot.children){
                    val user = snapshot.getValue(User::class.java)
                    userList.add(user!!)
                }
                userAdapter.notifyDataSetChanged()
            }

            override fun onCancelled(error: DatabaseError) {
                Toast.makeText(requireContext(), error.message, Toast.LENGTH_SHORT).show()
            }
        })
    }

User数据类 #

data class User(var id: String? = null,
                var username: String? = null,
                var imageurl: String? = null,
                var fullname: String? = null
)

崩溃Logcat信息 #

2022-10-02 04:12:26.041 17094-17094/com.data.app E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.data.app, PID: 17094
    java.lang.NullPointerException
        at com.data.app.adapter.UserAdapter.onBindViewHolder(UserAdapter.kt:47)
        at com.data.app.adapter.UserAdapter.onBindViewHolder(UserAdapter.kt:18)
        at androidx.recyclerview.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:7065)
        at androidx.recyclerview.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:7107)
        at androidx.recyclerview.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:6012)
        at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6279)
        at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6118)
        at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6114)
        at androidx.recyclerview.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2303)
        at androidx.recyclerview.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1627)
        at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1587)
        at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:665)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4134)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3851)
        at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4404)
        at android.view.View.layout(View.java:23147)
        at android.view.ViewGroup.layout(ViewGroup.java:6475)
        at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1873)
        at android.view.View.layout(View.java:23147)
        at android.view.ViewGroup.layout(ViewGroup.java:6475)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
        at android.view.View.layout(View.java:23147)
        at android.view.ViewGroup.layout(ViewGroup.java:6475)
        at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1873)
        at android.view.View.layout(View.java:23147)
        at android.view.ViewGroup.layout(ViewGroup.java:6475)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
        at android.view.View.layout(View.java:23147)
        at android.view.ViewGroup.layout(ViewGroup.java:6475)
        at androidx.appcompat.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:536)
        at android.view.View.layout(View.java:23147)
        at android.view.ViewGroup.layout(ViewGroup.java:6475)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
        at android.view.View.layout(View.java:23147)
        at android.view.ViewGroup.layout(ViewGroup.java:6475)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1841)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1673)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1582)
        at android.view.View.layout(View.java:23147)
        at android.view.ViewGroup.layout(ViewGroup.java:6475)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
        at com.android.internal.policy.DecorView.onLayout(DecorView.java:877)
        at android.view.View.layout(View.java:23147)
        at android.view.ViewGroup.layout(ViewGroup.java:6475)
        at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:3861)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:3272)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:2266)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:8854)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:1473)
        at android.view.Choreographer.doCallbacks(Choreographer.java:1270)
        at android.view.Choreographer.doFrame(Choreographer.java:981)
2022-10-02 04:12:26.042 17094-17094/com.project.thoughtwave E/AndroidRuntime:     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:1458)
        at android.os.Handler.handleCallback(Handler.java:938)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:263)
        at android.app.ActivityThread.main(ActivityThread.java:8296)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:612)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1006)

1. TextWatcher中的TODO触发异常：Kotlin的TODO()函数默认会抛出NotImplementedError，输入时beforeTextChanged和afterTextChanged方法会被调用，直接引发崩溃。
2. Firebase查询条件未生效：Firebase的startAt()、endAt()方法会返回新的Query对象，原代码单独调用这两个方法但未赋值，导致搜索条件没有应用到查询上。
3. Snapshot解析错误：遍历子节点时，错误使用父节点snapshot而非循环变量theSnapshot解析User对象，导致无法正确获取子节点数据，得到null实例，后续Adapter绑定访问null属性触发空指针。
4. 强制非空断言风险：使用user!!强制非空，若解析失败会直接抛出空指针异常。

1. 修正TextWatcher实现 #

移除TODO，改为空实现：

searchBar.addTextChangedListener(object : TextWatcher{
    override fun beforeTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {
        // 无需操作
    }

    override fun onTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {
        p0?.let {
            searchUser(it.toString().lowercase())
        }
    }

    override fun afterTextChanged(p0: Editable?) {
        // 无需操作
    }
})

2. 修正搜索方法 #

• 链式调用Firebase查询方法，正确应用搜索条件
• 使用循环变量theSnapshot解析子节点数据
• 增加空判断，避免null对象加入列表
• 使用addListenerForSingleValueEvent避免重复监听（若需实时更新，可保留addValueEventListener但需管理监听引用）

private fun searchUser(s: String) {
    // 链式调用，正确构建查询
    val query = FirebaseDatabase.getInstance()
        .getReference("Users")
        .orderByChild("username")
        .startAt(s)
        .endAt(s + "\uf8ff")

    query.addListenerForSingleValueEvent(object : ValueEventListener {
        @SuppressLint("NotifyDataSetChanged")
        override fun onDataChange(snapshot: DataSnapshot) {
            userList.clear()
            for (theSnapshot in snapshot.children) {
                // 使用循环变量获取子节点数据
                val user = theSnapshot.getValue(User::class.java)
                // 空判断后加入列表
                user?.let {
                    userList.add(it)
                }
            }
            userAdapter.notifyDataSetChanged()
        }

        override fun onCancelled(error: DatabaseError) {
            Toast.makeText(requireContext(), error.message, Toast.LENGTH_SHORT).show()
        }
    })
}

3. 可选优化 #

如果需要实时更新搜索结果，避免每次搜索新增监听，可保存之前的ValueEventListener引用，每次搜索前移除：

// 全局保存监听引用
private var searchListener: ValueEventListener? = null

private fun searchUser(s: String) {
    // 移除之前的监听
    searchListener?.let {
        FirebaseDatabase.getInstance().getReference("Users").removeEventListener(it)
    }

    val query = FirebaseDatabase.getInstance()
        .getReference("Users")
        .orderByChild("username")
        .startAt(s)
        .endAt(s + "\uf8ff")

    searchListener = object : ValueEventListener {
        @SuppressLint("NotifyDataSetChanged")
        override fun onDataChange(snapshot: DataSnapshot) {
            userList.clear()
            for (theSnapshot in snapshot.children) {
                val user = theSnapshot.getValue(User::class.java)
                user?.let {
                    userList.add(it)
                }
            }
            userAdapter.notifyDataSetChanged()
        }

        override fun onCancelled(error: DatabaseError) {
            Toast.makeText(requireContext(), error.message, Toast.LENGTH_SHORT).show()
        }
    }

    query.addValueEventListener(searchListener!!)
}

内容的提问来源于stack exchange，提问作者spunky.sukh