【发布时间】：2017-09-12 01:56:42
【问题描述】：
我是一名正在自学android的学生。 这是我的第一个问题。请帮帮我。
09-12 01:35:35.723 2355-2355/com.example.jan.sanhakproject E/AndroidRuntime:
FATAL EXCEPTION: main
Process: com.example.jan.sanhakproject, PID: 2355
com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type com.example.jan.sanhakproject.Chat
at com.google.android.gms.internal.zzbqi.zze(Unknown Source)
at com.google.android.gms.internal.zzbqi.zzb(Unknown Source)
at com.google.android.gms.internal.zzbqi.zza(Unknown Source)
at com.google.firebase.database.DataSnapshot.getValue(Unknown Source)
at com.example.jan.sanhakproject.ChatActivity$2.onChildAdded(ChatActivity.java:115)
at com.google.android.gms.internal.zzblz.zza(Unknown Source)
at com.google.android.gms.internal.zzbnz.zzYj(Unknown Source)
at com.google.android.gms.internal.zzboc$1.run(Unknown Source)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
09-12 01:35:44.318 2355-2374/com.example.jan.sanhakproject W/DynamiteModule: Local module descriptor class for com.google.firebase.auth not found.
Chat.java
公开课聊天{
public String email;
public String text;
public Chat() {
// Default constructor required for calls to DataSnapshot.getValue(Comment.class)
}
public Chat(String text) {
this.text = text;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public String getText() {
return text;
}
public void setText(String text) {
this.text = text;
}
}
ChatActivity.java
public class ChatActivity extends AppCompatActivity {
String TAG = this.getClass().getSimpleName();
private DatabaseReference mDatabase;
private FirebaseDatabase firebaseDatabase;
private RecyclerView mRecyclerView;
private RecyclerView.Adapter mAdapter;
private RecyclerView.LayoutManager mLayoutManager;
String[] myDataset = {"안녕", "오늘","뭐했어","영화볼래?"};
DatabaseReference databaseReference;
EditText etText;
Button btnSend;
String email;
List<Chat> mChat;
FirebaseDatabase database;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_chat);
firebaseDatabase = FirebaseDatabase.getInstance();
databaseReference = firebaseDatabase.getReference();
//database = FirebaseDatabase.getInstance();
FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
if (user != null) {
// Name, email address, and profile photo Url
email = user.getEmail();
}
Intent in = getIntent();
final String stChatId = in.getStringExtra("friendUid");
etText = (EditText) findViewById(R.id.etText);
btnSend = (Button) findViewById(R.id.btnSend);
btnSend.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
String stText = etText.getText().toString();
if (stText.equals("") || stText.isEmpty()) {
Toast.makeText(ChatActivity.this, "내용을 입력해 주세요.", Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(ChatActivity.this, email + "," + stText, Toast.LENGTH_SHORT).show();
Calendar c = Calendar.getInstance();
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String formattedDate = df.format(c.getTime());
databaseReference = database.getReference("users").child(stChatId).child(formattedDate);
Hashtable<String, String> chat = new Hashtable<String, String>();
chat.put("email", email);
chat.put("text", stText);
databaseReference.setValue(chat);
etText.setText("");
}
}
});
mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);
// use this setting to improve performance if you know that changes
// in content do not change the layout size of the RecyclerView
mRecyclerView.setHasFixedSize(true);
// use a linear layout manager
mLayoutManager = new LinearLayoutManager(this);
mRecyclerView.setLayoutManager(mLayoutManager);
mChat = new ArrayList<>();
// specify an adapter (see also next example)
mAdapter = new MyAdapter(mChat, email, ChatActivity.this);
mRecyclerView.setAdapter(mAdapter);
databaseReference.child("users").child(stChatId).child("chats").addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
Chat chat = dataSnapshot.getValue(Chat.class);
mChat.add(chat);
mRecyclerView.scrollToPosition(mChat.size() - 1);
mAdapter.notifyItemInserted(mChat.size() - 1);
}
@Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
@Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
}
MyAdapter.java
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
private String[] mDataset;
List<Chat> mChat;
String stEmail;
Context context;
// Provide a reference to the views for each data item
// Complex data items may need more than one view per item, and
// you provide access to all the views for a data item in a view holder public static class ViewHolder extends RecyclerView.ViewHolder {
// each data item is just a string in this case
public TextView mTextView;
public ViewHolder(View itemView) {
super(itemView);
mTextView = (TextView) itemView.findViewById(R.id.mTextView);
}
}
// Provide a suitable constructor (depends on the kind of dataset)
public MyAdapter(List<Chat> mChat, String email, Context context) {
this.mChat = mChat;
this.stEmail = email;
this.context = context;
}
@Override
public int getItemViewType(int position) {
if (mChat.get(position).getEmail().equals(stEmail)){
return 1;
} else {
return 2;
}
}
// Create new views (invoked by the layout manager)
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent,
int viewType) {
// create a new view
View v;
if (viewType == 1) {
v = LayoutInflater.from(parent.getContext())
.inflate(R.layout.right_text_view, parent, false);
} else {
v = LayoutInflater.from(parent.getContext())
.inflate(R.layout.my_text_view, parent, false);
}
// set the view's size, margins, paddings and layout parameters
ViewHolder vh = new ViewHolder(v);
return vh;
}
// Replace the contents of a view (invoked by the layout manager)
@Override
public void onBindViewHolder(ViewHolder holder, final int position) {
// - get element from your dataset at this position
// - replace the contents of the view with that element
holder.mTextView.setText(mChat.get(position).getText());
holder.mTextView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Toast.makeText(context, String.valueOf(position), Toast.LENGTH_SHORT).show();
}
});
}
// Return the size of your dataset (invoked by the layout manager)
@Override
public int getItemCount() {
return mChat.size();
}
}
【问题讨论】：
-
请说明您的问题，您为什么会收到该错误。我们没有足够的时间来阅读问题所在，因此您必须直接指定它并简化您的代码，您无需发布与错误无关的代码。
-
我想实时创建一个聊天应用，但是在接收数据的过程中，我想确保我得到了数据。原因：java。落后。 NullPointe rException : Can't match 'Failed' in greeting 产生错误。对不起。
-
您正在尝试使用具有空值的对象引用。或者可能在空引用引用的对象上调用实例方法。
-
@Deee No
null值似乎涉及此处：“无法将 java.lang.String 类型的对象转换为 com.example.jan.sanhakproject.Chat 类型” -
您在
databaseReference.child("users").child(stChatId).child("chats")中收听的位置下的一个节点未实现您在dataSnapshot.getValue(Chat.class)中尝试从中读取的类型。如果没有在该位置看到 JSON，很难说更多，您可以通过单击 Firebase Database console 中的“导出 JSON”链接获得。
标签： android firebase firebase-realtime-database