我正在使用Firebase构建聊天应用程序，其中我正在使用功能功能日志在android中显示通知。我创建了一个Reqactivity，如果某人向某人发送请求，该请求显示在他的同人android中，则如果某人单击问题是，如果这个小伙子android在前台运行该应用程序，并且他单击它，如果他单击后台通知应用程序由于错误而崩溃，那么如果他在后台运行，它将带他进入Reqactivity。 / p>
java.lang.RuntimeException：无法启动活动ComponentInfo {com.example.aquib.chatapp / com.example.aquib.chatapp.ProfileActivity}：java.lang.NullPointerException：println需要消息
这是我出错的地方
at com.example.aquib.chatapp.ProfileActivity.onCreate(ProfileActivity.java:64)
这是活动代码
//MessagingService Activity
String notification_click = remoteMessage.getNotification().getClickAction();
String notification_data = remoteMessage.getData().get("from_userId");
Intent intent = new Intent(notification_click);
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
intent.putExtra("user_id",notification_data);
//getting it over here ProfileActivity
final String User_Id = getIntent().getStringExtra("user_id");
currentUser = FirebaseAuth.getInstance().getCurrentUser();
progressDialog = new ProgressDialog(ProfileActivity.this);
databaseReference = FirebaseDatabase.getInstance().getReference().child("Users").child(User_Id);
databaseFriend =FirebaseDatabase.getInstance().getReference().child("Friends");
databaseReq = FirebaseDatabase.getInstance().getReference().child("Friend_Req");
databaseNotification = FirebaseDatabase.getInstance().getReference().child("Notification");
//updated
public class ProfileActivity extends AppCompatActivity {
DatabaseReference onData;
FirebaseAuth auth;
DatabaseReference databaseReq;
DatabaseReference databaseFriend;
DatabaseReference databaseReference;
DatabaseReference databaseNotification;
DatabaseReference mRootref;
ProgressDialog progressDialog;
FirebaseUser currentUser;
String mCurrentState;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_profile);
auth = FirebaseAuth.getInstance();
onData = FirebaseDatabase.getInstance().getReference().child("Users").child(auth.getCurrentUser().getUid());
final String User_Id = getIntent().getStringExtra("user_id");
mCurrentState = "not_friends";
final Button Decbutton = findViewById(R.id.button5);
final Button Reqbutton = findViewById(R.id.button4);
final TextView user_name = findViewById(R.id.textView5);
final TextView status_name = findViewById(R.id.textView6);
final ImageView profile_image = findViewById(R.id.imageView2);
currentUser = FirebaseAuth.getInstance().getCurrentUser();
progressDialog = new ProgressDialog(ProfileActivity.this);
databaseReference = FirebaseDatabase.getInstance().getReference().child("Users").child(User_Id);
databaseFriend = FirebaseDatabase.getInstance().getReference().child("Friends");
databaseReq = FirebaseDatabase.getInstance().getReference().child("Friend_Req");
databaseNotification = FirebaseDatabase.getInstance().getReference().child("Notification");
mRootref = FirebaseDatabase.getInstance().getReference();
progressDialog.setTitle("Loading User Data");
progressDialog.setMessage("Please wait while we load the data");
progressDialog.setCanceledOnTouchOutside(false);
progressDialog.show();
databaseReference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
String user = dataSnapshot.child("user").getValue().toString();
String status = dataSnapshot.child("status").getValue().toString();
String image = dataSnapshot.child("image").getValue().toString();
user_name.setText(user);
status_name.setText(status);
Picasso.with(ProfileActivity.this).load(image).into(profile_image);
// -------------------- Friend List / Request Feature--------------------
databaseReq.child(currentUser.getUid()).addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.hasChild(User_Id)) {
String req_type = dataSnapshot.child(User_Id).child("request_type").getValue().toString();
if (req_type.equals("received")) {
Reqbutton.setText("Accept Friend Request");
mCurrentState = "req_received";
Decbutton.setVisibility(View.VISIBLE);
} else if (req_type.equals("sent")) {
mCurrentState = "req_sent";
Reqbutton.setText("Cancel Friend Request");
Decbutton.setVisibility(View.INVISIBLE);
}
progressDialog.dismiss();
} else {
databaseFriend.child(currentUser.getUid()).addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.hasChild(User_Id)) {
Reqbutton.setText("Unfriend this Person");
mCurrentState = "friends";
Decbutton.setVisibility(View.INVISIBLE);
}
progressDialog.dismiss();
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
progressDialog.dismiss();
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
// -------------------- Friend Request--------------------
Reqbutton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Reqbutton.setEnabled(false);
// -------------------- Not Friend State --------------------
if (mCurrentState.equals("not_friends")) {
DatabaseReference newNotifref = mRootref.child("Notification").child(User_Id).push();
String newNotifId = newNotifref.getKey();
HashMap<String, String> hashMap = new HashMap<>();
hashMap.put("from", currentUser.getUid());
hashMap.put("type", "request");
Map requestMap = new HashMap();
requestMap.put("Friend_Req/" + currentUser.getUid() + "/" + User_Id + "/" + "request_type", "sent");
requestMap.put("Friend_Req/" + User_Id + "/" + currentUser.getUid() + "/" + "request_type", "received");
requestMap.put("Notification/" + User_Id + "/" + newNotifId, hashMap);
mRootref.updateChildren(requestMap, new DatabaseReference.CompletionListener() {
@Override
public void onComplete(DatabaseError databaseError, DatabaseReference databaseReference) {
if (databaseError == null) {
Reqbutton.setEnabled(true);
Reqbutton.setText("Cancel Friend Request");
Reqbutton.setBackground(getResources().getDrawable(R.color.colorBtn));
mCurrentState = "req_sent";
Decbutton.setVisibility(View.INVISIBLE);
} else {
Toast.makeText(ProfileActivity.this, "There was some error in sending request", Toast.LENGTH_SHORT).show();
}
Reqbutton.setEnabled(true);
}
});
}
// -------------------- Cancel Friend Request--------------------
if (mCurrentState.equals("req_sent")) {
Map map = new HashMap();
map.put("Friend_Req/" + currentUser.getUid() + "/" + User_Id, null);
map.put("Friend_Req/" + User_Id + "/" + currentUser.getUid(), null);
mRootref.updateChildren(map, new DatabaseReference.CompletionListener() {
@Override
public void onComplete(DatabaseError databaseError, DatabaseReference databaseReference) {
if (databaseError == null) {
Reqbutton.setEnabled(true);
Reqbutton.setText("Send Friend Request");
mCurrentState = "not_friends";
Decbutton.setVisibility(View.INVISIBLE);
} else {
Toast.makeText(ProfileActivity.this, "Error in doing it", Toast.LENGTH_SHORT).show();
}
}
});
// -------------------- Req Received State --------------------
if (mCurrentState.equals("req_received")) {
final String currentDate = DateFormat.getDateInstance().format(new Date());
Map map = new HashMap();
map.put("Friends/" + currentUser.getUid() + "/" + User_Id + "/date", currentDate);
map.put("Friends/" + User_Id + "/" + currentUser.getUid() + "/date", currentDate);
map.put("Friend_Req/" + currentUser.getUid() + "/" + User_Id, null);
map.put("Friend_Req/" + User_Id + "/" + currentUser.getUid(), null);
mRootref.updateChildren(map, new DatabaseReference.CompletionListener() {
@Override
public void onComplete(DatabaseError databaseError, DatabaseReference databaseReference) {
if (databaseError == null) {
Reqbutton.setText("Unfriend this Person");
Reqbutton.setEnabled(true);
mCurrentState = "friends";
Decbutton.setVisibility(View.INVISIBLE);
} else {
Toast.makeText(ProfileActivity.this, "Error in Receiving", Toast.LENGTH_SHORT).show();
}
}
});
//----------------- UnFriend ----------------------
if (mCurrentState.equals("friends")) {
Map map = new HashMap();
map.put("Friends/" + currentUser.getUid() + "/" + User_Id, null);
map.put("Friends/" + User_Id + "/" + currentUser.getUid(), null);
mRootref.updateChildren(map, new DatabaseReference.CompletionListener() {
@Override
public void onComplete(DatabaseError databaseError, DatabaseReference databaseReference) {
if (databaseError == null) {
mCurrentState = "not_friends";
Reqbutton.setEnabled(true);
Reqbutton.setText("Send Friend Request");
Decbutton.setVisibility(View.INVISIBLE);
} else {
Toast.makeText(ProfileActivity.this, databaseError.getMessage().toString(), Toast.LENGTH_SHORT).show();
}
}
});
}
}
});
Decbutton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Map map = new HashMap();
map.put("Friend_Req/" + currentUser.getUid() + "/" + User_Id, null);
map.put("Friend_Req/" + User_Id + "/" + currentUser.getUid(), null);
mRootref.updateChildren(map, new DatabaseReference.CompletionListener() {
@Override
public void onComplete(DatabaseError databaseError, DatabaseReference databaseReference) {
if (databaseError == null) {
Decbutton.setVisibility(View.INVISIBLE);
Reqbutton.setText("Send Friend Request");
mCurrentState = "not_friends";
} else {
Toast.makeText(ProfileActivity.this, "Error in the dec btn", Toast.LENGTH_SHORT).show();
}
}
});
}
});
}
}
答案 0 :(得分：0)
java.lang.NullPointerException： println需要消息
您可能需要将一条消息设置为println，例如以下代码：
System.out.println("Your message");
但是，这不是重点。那是纯Java，我们使用println作为。 最好使用登录android开发。 （您也可以同时使用）