我正在嘗試制作一個從實時 Firebase 數據庫獲取數據的微調器。我在我的日志語句中很好地提取了數據，當我按下下拉菜單時，我也看到了我的數據。但是當我嘗試在微調器中選擇某些內容時，它不會設置數據。此外，當我嘗試調用我的 getSelectedItem() 方法時，它給了我錯誤java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference在我寫的日志中沒有空值，因此我很困惑為什么我會收到這種錯誤import android.content.Intent;import android.support.annotation.NonNull;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.util.Log;import android.view.View;import android.widget.ArrayAdapter;import android.widget.EditText;import android.widget.Spinner;import com.example.bankapp.BankAccount;import com.example.bankapp.R;import com.google.firebase.database.DataSnapshot;import com.google.firebase.database.DatabaseError;import com.google.firebase.database.DatabaseReference;import com.google.firebase.database.FirebaseDatabase;import com.google.firebase.database.ValueEventListener;import java.util.ArrayList;public class TransferOwnAccount extends AppCompatActivity { private Spinner accountFrom, accountTo; private EditText transferAmount; private FirebaseDatabase database; ArrayList<BankAccount> accounts = new ArrayList<>(); @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_transfer_own_account); init(); loadAccounts(); } public void transferMoney(View view) { Log.d("grinern", "olool"+accountFrom.getSelectedItem().toString()); }它應該選擇我在下拉微調器中按下的任何內容，并在我的日志中打印它，這是在我的 transferMoney() 方法中調用的
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TA貢獻1821條經驗 獲得超5個贊
您需要將 bankaccounts arraylist 更改為靜態（以確保即使狀態發生變化也是如此）
然后我將適配器作為一個字段移動并在 init 方法中對其進行了初始化，檢查我提供的代碼：
package com.example.bankapp;
import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.Spinner;
import com.example.bankapp.BankAccount;
import com.example.bankapp.R;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
import java.util.ArrayList;
public class TransferOwnAccount extends AppCompatActivity {
private Spinner accountFrom, accountTo;
private EditText transferAmount;
private FirebaseDatabase database;
static ArrayList<BankAccount> accounts = new ArrayList<>();
ArrayAdapter<BankAccount> adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_transfer_own_account);
init();
loadAccounts();
}
public void transferMoney(View view) {
Log.d("test", "olool" + accountFrom.getSelectedItem().toString());
}
public void loadAccounts() {
Intent getIntent = getIntent();
String userCPR = getIntent.getStringExtra("CPR");
DatabaseReference dbref = database.getReference("usersbankaccounts/" + userCPR);
dbref.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot data : dataSnapshot.getChildren()) {
DatabaseReference bankaccounts = database.getReference("bankaccounts/" + data.getKey());
Log.d("test", data.getKey());
bankaccounts.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
BankAccount bankAccount = dataSnapshot.getValue(BankAccount.class);
accounts.add(bankAccount);
adapter.notifyDataSetChanged();
Log.d("test", "" + accounts);
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
Log.d("test", "" + accounts);
adapter.notifyDataSetChanged();
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
public void init() {
this.adapter = new ArrayAdapter<>(this, android.R.layout.simple_dropdown_item_1line, accounts);
this.accountFrom = findViewById(R.id.transferFromSpinner);
this.accountTo = findViewById(R.id.transferToSpinner);
this.transferAmount = findViewById(R.id.transferAmount);
this.database = FirebaseDatabase.getInstance();
this.accountFrom.setAdapter(adapter);
this.accountTo.setAdapter(adapter);
}
}
然后你需要確保你的銀行賬戶中有一個 toString() 方法
@Override
public String toString() {
return title + "--- " +accNumber + " " + balance ;
}
這應該可以解決問題:)
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