更新和洗掉功能在Firebase中不起作用-有解無憂

我正在開發一個巴士預訂應用程式。但是我的更新和洗掉功能有問題。我可以更新時間和價格。但是每當我嘗試更新源或目的地或巴士號碼時......我的應用程式就會卡住。當我檢查我的 Firebase 實時資料庫時......它看起來好像該值陷入了無限回圈......作為更新的值......不斷從舊值更改為新值，新值更改為舊值不斷地。這導致我的應用程式卡住了。我有兩個關于這個的檔案。

編輯總線.java

package com.example.busticketbooking;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

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.HashMap;
import java.util.Map;

public class Edit_Bus extends AppCompatActivity {
   //Variables
   public EditText busNumEdit,srcEdit,destEdit,timingsEdit,priceEdit;
   private DatabaseReference databaseReference;
   public String BusID;

   @Override
   protected void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.activity_edit_bus);
       busNumEdit =findViewById(R.id.BusNumber);
       srcEdit=findViewById(R.id.source);
       destEdit=findViewById(R.id.dest);
       timingsEdit=findViewById(R.id.timings);
       priceEdit=findViewById(R.id.price);
       Button deleteButton = findViewById(R.id.deletebtn);
       Button updateButton = findViewById(R.id.updatebtn);
       FirebaseDatabase firebaseDatabase = FirebaseDatabase.getInstance();

       BusRVModel busRVModel = getIntent().getParcelableExtra("Bus");
       if(busRVModel !=null){
           busNumEdit.setText(busRVModel.getBusNum());
           srcEdit.setText(busRVModel.getSrc());
           destEdit.setText(busRVModel.getDest());
           timingsEdit.setText(busRVModel.getTimings());
           priceEdit.setText(busRVModel.getPrice());
           BusID= busRVModel.getBusID();
       }

       databaseReference= firebaseDatabase.getReference("Bus").child(BusID);
       updateButton.setOnClickListener(new View.OnClickListener() {
           @Override
           public void onClick(View view) {
               String busNumVar= busNumEdit.getText().toString();
               String srcVar=srcEdit.getText().toString();
               String destVar=destEdit.getText().toString();
               String timingsVar=timingsEdit.getText().toString();
               String priceVar=priceEdit.getText().toString();

               Map<String,Object> map=new HashMap<>();
               map.put("busNum", busNumVar);
               map.put("src",srcVar);
               map.put("dest",destVar);
               map.put("timings",timingsVar);
               map.put("price",priceVar);
               map.put("busID",BusID);

               databaseReference.addValueEventListener(new ValueEventListener() {
                   @Override
                   public void onDataChange(@NonNull DataSnapshot snapshot) {
                       databaseReference.updateChildren(map);
                       Toast.makeText(Edit_Bus.this, "Bus updated", Toast.LENGTH_SHORT).show();
                       startActivity(new Intent(Edit_Bus.this,MainActivity2.class));

                   }

                   @Override
                   public void onCancelled(@NonNull DatabaseError error) {
                       Toast.makeText(Edit_Bus.this, "Update Error", Toast.LENGTH_SHORT).show();
                   }
               });
           }
       });

       deleteButton.setOnClickListener(new View.OnClickListener() {
           @Override
           public void onClick(View view) {
               deleteBus();
           }
       });
   }
   private void deleteBus(){
       databaseReference.removeValue();
       Toast.makeText(this, "Bus Deleted!!!", Toast.LENGTH_SHORT).show();
       startActivity(new Intent(Edit_Bus.this,MainActivity2.class));
   }
}

BusRVModel.java

package com.example.busticketbooking;

import android.os.Parcel;
import android.os.Parcelable;

import java.util.ArrayList;

public class BusRVModel implements Parcelable{
    private String busNum;
    private String src;
    private String dest;
    private String timings;
    private String price;
    private String BusID;

    public BusRVModel() {
    }

    public BusRVModel(String busNum, String src, String dest, String timings, String price, String busID ) {
        this.busNum = busNum;
        this.src = src;
        this.dest = dest;
        this.timings = timings;
        this.price = price;
        BusID = busID;
    }

    protected BusRVModel(Parcel in) {
        busNum = in.readString();
        src = in.readString();
        dest = in.readString();
        timings = in.readString();
        price = in.readString();
        BusID = in.readString();
    }

    public static final Creator<BusRVModel> CREATOR = new Creator<BusRVModel>() {
        @Override
        public BusRVModel createFromParcel(Parcel in) {
            return new BusRVModel(in);
        }

        @Override
        public BusRVModel[] newArray(int size) {
            return new BusRVModel[size];
        }
    };

    public String getBusNum() {
        return busNum;
    }

    public void setBusNum(String busNum) {
        this.busNum = busNum;
    }

    public String getSrc() {
        return src;
    }

    public void setSrc(String src) {
        this.src = src;
    }

    public String getDest() {
        return dest;
    }

    public void setDest(String dest) {
        this.dest = dest;
    }

    public String getTimings() {
        return timings;
    }

    public void setTimings(String timings) {
        this.timings = timings;
    }

    public String getPrice() {
        return price;
    }

    public void setPrice(String price) {
        this.price = price;
    }

    public String getBusID() {
        return BusID;
    }

    public void setBusID(String busID) {
        BusID = busID;
    }

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel parcel, int i) {
        parcel.writeString(busNum);
        parcel.writeString(src);
        parcel.writeString(dest);
        parcel.writeString(timings);
        parcel.writeString(price);
        parcel.writeString(BusID);
    }
}

AddBus.java

package com.example.busticketbooking;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

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;

public class Add_Bus extends AppCompatActivity {
    private EditText busNum,src,dest,timings,price;
    private Button button;
    private FirebaseDatabase firebaseDatabase;
    private DatabaseReference databaseReference;
    private String BusID;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_add_bus);
        busNum=findViewById(R.id.BusNumber);
        src=findViewById(R.id.source);
        dest=findViewById(R.id.dest);
        timings=findViewById(R.id.timings);
        price=findViewById(R.id.price);
        button=findViewById(R.id.btn);
        firebaseDatabase=FirebaseDatabase.getInstance();
        databaseReference=firebaseDatabase.getReference("Bus");

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String busNumVar=busNum.getText().toString();
                String srcVar=src.getText().toString();
                String destVar=dest.getText().toString();
                String timingsVar=timings.getText().toString();
                String priceVar=price.getText().toString();
                BusID=busNumVar;
                BusRVModel busRVModel=new BusRVModel(busNumVar,srcVar,destVar,timingsVar,priceVar,BusID);
                databaseReference.addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot snapshot) {

                        databaseReference.child(BusID).setValue(busRVModel);
                        Toast.makeText(Add_Bus.this, "Bus added", Toast.LENGTH_SHORT).show();
                        startActivity(new Intent(Add_Bus.this,MainActivity2.class));
                    }

                    @Override
                    public void onCancelled(@NonNull DatabaseError error) {
                        Toast.makeText(Add_Bus.this, "Error is: " error.toString(), Toast.LENGTH_SHORT).show();
                    }
                });
            }
        });
    }
}

uj5u.com熱心網友回復：

問題在這里：

databaseReference.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot snapshot) {
        databaseReference.updateChildren(map);
        Toast.makeText(Edit_Bus.this, "Bus updated", Toast.LENGTH_SHORT).show();
        startActivity(new Intent(Edit_Bus.this,MainActivity2.class));

    }

    @Override
    public void onCancelled(@NonNull DatabaseError error) {
        Toast.makeText(Edit_Bus.this, "Update Error", Toast.LENGTH_SHORT).show();
    }
});

您通過呼叫將偵聽器添加到資料庫中addValueEventListener，記錄為：

此方法在附加偵聽器時觸發一次，并且在每次資料（包括子項）發生更改時再次觸發。

現在在里面onDataChange你修改資料databaseReference，正如檔案所說，這會導致onDataChange再次被呼叫，這會導致你再次更新資料，這會導致......

由于您似乎只想更新一次資料，您可以使用它addListenerForSingleValueEvent來防止重新觸發onDataChange：

                  // ??
databaseReference.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot snapshot) {
        ...

轉載請註明出處，本文鏈接：https://www.uj5u.com/houduan/492812.html

標籤：爪哇安卓火力基地 firebase-实时数据库

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