如何从 Firebase 数据库中检索特定数据
How to retrieve a particular data from Firebase database
我正在做一个用户将基于角色登录的应用程序。管理员和员工都需要一份申请。
在这里，当管理员喜欢它时，它应该显示一个不同的仪表板，我们该怎么做，据我所知，我有点厌倦了检索当前用户的角色，但对我来说，它在 firebaseuser 中显示空指针异常.
package com.example.loginregistration;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.text.TextUtils;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.Toast;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
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.Query;
import com.google.firebase.database.ValueEventListener;
import com.rengwuxian.materialedittext.MaterialEditText;
public class MainActivity extends AppCompatActivity {
MaterialEditText email,password;
Button login, register;
FirebaseAuth fAuth;
FirebaseUser User;
DatabaseReference reff;
String Role="";
CheckBox loginstate;
Query query,query1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
email = findViewById(R.id.email);
password = findViewById(R.id.password);
fAuth = FirebaseAuth.getInstance();
//loginstate = findViewById(R.id.checkbox);
login = findViewById(R.id.login);
register = findViewById(R.id.register);
//query = FirebaseDatabase.getInstance().getReference().child("Employee").orderByChild("role");
//query1 = FirebaseDatabase.getInstance().getReference().child("Employee").orderByChild(User.getUid()).equalTo("role");
//final Query query1 = FirebaseDatabase.getInstance().getReference().child("Employee").orderByChild("Role").equalTo("User");
login.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//String txtUserName = userName.getText().toString();
String txtEmail = email.getText().toString().trim();
String txtPassword = password.getText().toString().trim();
//String txtMobile = mobile.getText().toString();
if (TextUtils.isEmpty(txtEmail)){
email.setError("Email is Required.");
return;
}
if (TextUtils.isEmpty(txtPassword)){
password.setError("Password is Required.");
return;
}
if (password.length() < 6){
password.setError("Password must be more than 6 characters.");
return;
}
fAuth.signInWithEmailAndPassword(txtEmail,txtPassword).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
@Override
public void onComplete(@NonNull Task<AuthResult> task) {
if (task.isSuccessful()){
retrieve();
String user = task.getResult().getUser().getUid();
if (Role.equals("Admin")){
Toast.makeText(MainActivity.this,"Logged in successfully.",Toast.LENGTH_SHORT).show();
startActivity(new Intent(getApplicationContext(),AppStartActivity.class));
}
else {
Toast.makeText(MainActivity.this,"Logged in successfully.",Toast.LENGTH_SHORT).show();
startActivity(new Intent(getApplicationContext(),AppStartActivity.class));
}
}
/*else if (task.isSuccessful() && Role.equals("User")) {
Toast.makeText(MainActivity.this,"Logged in successfully.",Toast.LENGTH_SHORT).show();
startActivity(new Intent(getApplicationContext(),EmpStarActivity.class));
}
*/
else {
Toast.makeText(MainActivity.this, "Error ! " + task.getException().getMessage(), Toast.LENGTH_SHORT).show();
}
}
});
}
});
}
private void retrieve(){
User = fAuth.getCurrentUser();
reff = FirebaseDatabase.getInstance().getReference().child(User.getUid());
reff.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
/*for (DataSnapshot snap : dataSnapshot.getChildren())
{*/
//Employee student = dataSnapshot.getValue(Employee.class);
//Log.d("TAG","name: "+student.getRole());
//Role = dataSnapshot.child("Admin").getValue(String.class);
String Role = dataSnapshot.child("role").getValue().toString();
//String prize = dataSnapshot.child("prize").getValue().toString();
Log.e("Role", Role);
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
}
我的数据库看起来像
我想检查这个人是admin是不是user的条件，然后据此显示activity。
这里列出了错误
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.google.firebase.auth.FirebaseUser.getUid()' on a null object reference
at com.example.loginregistration.MainActivity.onCreate(MainActivity.java:53)
at android.app.Activity.performCreate(Activity.java:7136)
at android.app.Activity.performCreate(Activity.java:7127)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
2020-04-16 19:02:12.431 1943-1978/system_process E/BatteryExternalStatsWorker: no controller energy info supplied for wifi
2020-04-16 19:02:13.267 1622-2110/? E/AudioPolicyIntefaceImpl: getInputForAttr permission denied: recording not allowed for uid 10023 pid 3445
2020-04-16 19:02:13.267 1622-2110/? E/AudioFlinger: createRecord() checkRecordThread_l failed
2020-04-16 19:02:13.267 3445-18622/com.google.android.googlequicksearchbox:search E/IAudioFlinger: createRecord returned error -22
2020-04-16 19:02:13.267 3445-18622/com.google.android.googlequicksearchbox:search E/AudioRecord: AudioFlinger could not create record track, status: -22
2020-04-16 19:02:13.267 3445-18622/com.google.android.googlequicksearchbox:search E/AudioRecord-JNI: Error creating AudioRecord instance: initialization check failed with status -22.
2020-04-16 19:02:13.269 3445-18622/com.google.android.googlequicksearchbox:search E/android.media.AudioRecord: Error code -20 when initializing native AudioRecord object.
2020-04-16 19:02:13.272 3445-18622/com.google.android.googlequicksearchbox:search E/ActivityThread: Failed to find provider info for com.google.android.apps.gsa.testing.ui.audio.recorded
2020-04-16 19:02:18.343 1622-2110/? E/AudioPolicyIntefaceImpl: getInputForAttr permission denied: recording not allowed for uid 10023 pid 3445
2020-04-16 19:02:18.343 1622-2110/? E/AudioFlinger: createRecord() checkRecordThread_l failed
2020-04-16 19:02:18.344 3445-18622/com.google.android.googlequicksearchbox:search E/IAudioFlinger: createRecord returned error -22
2020-04-16 19:02:18.344 3445-18622/com.google.android.googlequicksearchbox:search E/AudioRecord: AudioFlinger could not create record track, status: -22
2020-04-16 19:02:18.345 3445-18622/com.google.android.googlequicksearchbox:search E/AudioRecord-JNI: Error creating AudioRecord instance: initialization check failed with status -22.
2020-04-16 19:02:18.346 3445-18622/com.google.android.googlequicksearchbox:search E/android.media.AudioRecord: Error code -20 when initializing native AudioRecord object.
2020-04-16 19:02:18.347 3445-18622/com.google.android.googlequicksearchbox:search E/ActivityThread: Failed to find provider info for com.google.android.apps.gsa.testing.ui.audio.
您甚至无法在登录应用程序之前检索 uid。
在 if(task.isSuccessful()){ 中执行以下操作：
String user = task.getResult().getUser().getUid();
然后您可以在您的 dB 参考中使用它
尝试以下方法检索角色：
private void retrieve(){
//User = fAuth.getCurrentUser();
reff = FirebaseDatabase.getInstance().getReference().child("Employee").child("Admin");
reff.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
/*for (DataSnapshot snap : dataSnapshot.getChildren())
{*/
//Employee student = dataSnapshot.getValue(Employee.class);
//Log.d("TAG","name: "+student.getRole());
//Role = dataSnapshot.child("Admin").getValue(String.class);
String Role = dataSnapshot.child("role").getValue().toString();
//String prize = dataSnapshot.child("prize").getValue().toString();
Log.e("Role", Role);
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
我正在做一个用户将基于角色登录的应用程序。管理员和员工都需要一份申请。
在这里，当管理员喜欢它时，它应该显示一个不同的仪表板，我们该怎么做，据我所知，我有点厌倦了检索当前用户的角色，但对我来说，它在 firebaseuser 中显示空指针异常.
package com.example.loginregistration;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.text.TextUtils;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.Toast;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
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.Query;
import com.google.firebase.database.ValueEventListener;
import com.rengwuxian.materialedittext.MaterialEditText;
public class MainActivity extends AppCompatActivity {
MaterialEditText email,password;
Button login, register;
FirebaseAuth fAuth;
FirebaseUser User;
DatabaseReference reff;
String Role="";
CheckBox loginstate;
Query query,query1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
email = findViewById(R.id.email);
password = findViewById(R.id.password);
fAuth = FirebaseAuth.getInstance();
//loginstate = findViewById(R.id.checkbox);
login = findViewById(R.id.login);
register = findViewById(R.id.register);
//query = FirebaseDatabase.getInstance().getReference().child("Employee").orderByChild("role");
//query1 = FirebaseDatabase.getInstance().getReference().child("Employee").orderByChild(User.getUid()).equalTo("role");
//final Query query1 = FirebaseDatabase.getInstance().getReference().child("Employee").orderByChild("Role").equalTo("User");
login.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//String txtUserName = userName.getText().toString();
String txtEmail = email.getText().toString().trim();
String txtPassword = password.getText().toString().trim();
//String txtMobile = mobile.getText().toString();
if (TextUtils.isEmpty(txtEmail)){
email.setError("Email is Required.");
return;
}
if (TextUtils.isEmpty(txtPassword)){
password.setError("Password is Required.");
return;
}
if (password.length() < 6){
password.setError("Password must be more than 6 characters.");
return;
}
fAuth.signInWithEmailAndPassword(txtEmail,txtPassword).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
@Override
public void onComplete(@NonNull Task<AuthResult> task) {
if (task.isSuccessful()){
retrieve();
String user = task.getResult().getUser().getUid();
if (Role.equals("Admin")){
Toast.makeText(MainActivity.this,"Logged in successfully.",Toast.LENGTH_SHORT).show();
startActivity(new Intent(getApplicationContext(),AppStartActivity.class));
}
else {
Toast.makeText(MainActivity.this,"Logged in successfully.",Toast.LENGTH_SHORT).show();
startActivity(new Intent(getApplicationContext(),AppStartActivity.class));
}
}
/*else if (task.isSuccessful() && Role.equals("User")) {
Toast.makeText(MainActivity.this,"Logged in successfully.",Toast.LENGTH_SHORT).show();
startActivity(new Intent(getApplicationContext(),EmpStarActivity.class));
}
*/
else {
Toast.makeText(MainActivity.this, "Error ! " + task.getException().getMessage(), Toast.LENGTH_SHORT).show();
}
}
});
}
});
}
private void retrieve(){
User = fAuth.getCurrentUser();
reff = FirebaseDatabase.getInstance().getReference().child(User.getUid());
reff.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
/*for (DataSnapshot snap : dataSnapshot.getChildren())
{*/
//Employee student = dataSnapshot.getValue(Employee.class);
//Log.d("TAG","name: "+student.getRole());
//Role = dataSnapshot.child("Admin").getValue(String.class);
String Role = dataSnapshot.child("role").getValue().toString();
//String prize = dataSnapshot.child("prize").getValue().toString();
Log.e("Role", Role);
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
}
我的数据库看起来像
我想检查这个人是admin是不是user的条件，然后据此显示activity。
这里列出了错误
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.google.firebase.auth.FirebaseUser.getUid()' on a null object reference
at com.example.loginregistration.MainActivity.onCreate(MainActivity.java:53)
at android.app.Activity.performCreate(Activity.java:7136)
at android.app.Activity.performCreate(Activity.java:7127)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
2020-04-16 19:02:12.431 1943-1978/system_process E/BatteryExternalStatsWorker: no controller energy info supplied for wifi
2020-04-16 19:02:13.267 1622-2110/? E/AudioPolicyIntefaceImpl: getInputForAttr permission denied: recording not allowed for uid 10023 pid 3445
2020-04-16 19:02:13.267 1622-2110/? E/AudioFlinger: createRecord() checkRecordThread_l failed
2020-04-16 19:02:13.267 3445-18622/com.google.android.googlequicksearchbox:search E/IAudioFlinger: createRecord returned error -22
2020-04-16 19:02:13.267 3445-18622/com.google.android.googlequicksearchbox:search E/AudioRecord: AudioFlinger could not create record track, status: -22
2020-04-16 19:02:13.267 3445-18622/com.google.android.googlequicksearchbox:search E/AudioRecord-JNI: Error creating AudioRecord instance: initialization check failed with status -22.
2020-04-16 19:02:13.269 3445-18622/com.google.android.googlequicksearchbox:search E/android.media.AudioRecord: Error code -20 when initializing native AudioRecord object.
2020-04-16 19:02:13.272 3445-18622/com.google.android.googlequicksearchbox:search E/ActivityThread: Failed to find provider info for com.google.android.apps.gsa.testing.ui.audio.recorded
2020-04-16 19:02:18.343 1622-2110/? E/AudioPolicyIntefaceImpl: getInputForAttr permission denied: recording not allowed for uid 10023 pid 3445
2020-04-16 19:02:18.343 1622-2110/? E/AudioFlinger: createRecord() checkRecordThread_l failed
2020-04-16 19:02:18.344 3445-18622/com.google.android.googlequicksearchbox:search E/IAudioFlinger: createRecord returned error -22
2020-04-16 19:02:18.344 3445-18622/com.google.android.googlequicksearchbox:search E/AudioRecord: AudioFlinger could not create record track, status: -22
2020-04-16 19:02:18.345 3445-18622/com.google.android.googlequicksearchbox:search E/AudioRecord-JNI: Error creating AudioRecord instance: initialization check failed with status -22.
2020-04-16 19:02:18.346 3445-18622/com.google.android.googlequicksearchbox:search E/android.media.AudioRecord: Error code -20 when initializing native AudioRecord object.
2020-04-16 19:02:18.347 3445-18622/com.google.android.googlequicksearchbox:search E/ActivityThread: Failed to find provider info for com.google.android.apps.gsa.testing.ui.audio.
您甚至无法在登录应用程序之前检索 uid。
在 if(task.isSuccessful()){ 中执行以下操作：
String user = task.getResult().getUser().getUid();
然后您可以在您的 dB 参考中使用它
尝试以下方法检索角色：
private void retrieve(){
//User = fAuth.getCurrentUser();
reff = FirebaseDatabase.getInstance().getReference().child("Employee").child("Admin");
reff.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
/*for (DataSnapshot snap : dataSnapshot.getChildren())
{*/
//Employee student = dataSnapshot.getValue(Employee.class);
//Log.d("TAG","name: "+student.getRole());
//Role = dataSnapshot.child("Admin").getValue(String.class);
String Role = dataSnapshot.child("role").getValue().toString();
//String prize = dataSnapshot.child("prize").getValue().toString();
Log.e("Role", Role);
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}