我正在尝试开发一个Android应用程序,如果其中存在该值,我可以删除其中的值。如果删除了值,则该值应为true;如果该值不存在,则应抛出错误。我正在使用Firebase实时数据库。
我正在尝试执行if-else语句,但是我无法成功
package com.vi.dhananjay.lol;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.os.Bundle;
import android.widget.TextView;
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 MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button del = (Button) findViewById(R.id.delButton);
Button eb = (Button) findViewById(R.id.ebDelete);
Button teac = (Button) findViewById(R.id.teaDelete);
Button csd = (Button) findViewById(R.id.conDelete);
Button hosp = (Button) findViewById(R.id.hosDelete);
TextView qrCode = (TextView) findViewById(R.id.qrCode);
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
rootRef.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
void deleDelete(DataSnapshot snapshot) {
if (snapshot.hasChild("qrCode")) {
// run some code
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
eb.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
ebDelete();
}
});
teac.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
teacDelete();
}
});
csd.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
csdDelete();
}
});
hosp.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
hospDelete();
}
});
del.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
deleDelete();
}
});
}
private void deleDelete() {
DatabaseReference qrcode = FirebaseDatabase.getInstance().getReference("delegates");
qrcode.removeValue();
Toast.makeText(this, "Code validated", Toast.LENGTH_LONG).show();
}
private void ebDelete() {
DatabaseReference qrcode = FirebaseDatabase.getInstance().getReference("delegates");
qrcode.removeValue();
Toast.makeText(this, "Code validated", Toast.LENGTH_LONG).show();
}
private void teacDelete() {
DatabaseReference qrcode = FirebaseDatabase.getInstance().getReference("delegates");
qrcode.removeValue();
Toast.makeText(this, "Code validated", Toast.LENGTH_LONG).show();
}
private void csdDelete() {
DatabaseReference qrcode = FirebaseDatabase.getInstance().getReference("delegates");
qrcode.removeValue();
Toast.makeText(this, "Code validated", Toast.LENGTH_LONG).show();
}
private void hospDelete() {
DatabaseReference qrcode = FirebaseDatabase.getInstance().getReference("delegates");
qrcode.removeValue();
Toast.makeText(this, "Code validated", Toast.LENGTH_LONG).show();
}
}
出现的错误
错误:不是抽象的,并且不会覆盖ValueEventListener中的抽象方法onDataChange(DataSnapshot)
答案 0 :(得分:0)
实现ValueEventListener
时,必须实现该接口的两种方法:onDataChange
和onCancelled
。看来您将onDataChange
的名称更改为deleDelete
,这意味着编译器不再能找到onDataChange
,从而导致错误。
要解决此问题,请将deleDelete
重命名为onDataChange
:
rootRef.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
void onDataChange(DataSnapshot snapshot) {
if (snapshot.hasChild("qrCode")) {
// run some code
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
throw databaseError.toException(); // don't ignore errors
}
});
如果您想使用deleDelete
方法名称来简化说明,可以将其包含在实现中。您只需要确保仍然实现onDataChange
,否则编译器将不知道该怎么做。
类似这样:
rootRef.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
void onDataChange(DataSnapshot snapshot) {
deleteDelete(snapshot)
}
void deleteDelete(DataSnapshot snapshot) {
if (snapshot.hasChild("qrCode")) {
// run some code
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
throw databaseError.toException(); // don't ignore errors
}
});
您会注意到,deleteDelete
在这里没有用@Override
标记,因为它没有覆盖/实现ValueEventListener
中的方法。