我的目标是让用户点击列表视图，它将转到页面，让用户修改数据，然后更新到数据库。
这是数据库参考： https://imgur.com/6Qx10ll
此外，在项目onclick上，我想将位置的数据发送到修改页面。但错误是
java.lang.NullPointerException: Attempt to invoke virtual method
'java.lang.String java.lang.Object.toString()' on a null object reference
at com.example.fjuim.tronclass.Me.MeTodolist$2$1.onDataChange(MeTodolist.java:89)
at com.google.firebase.database.zzp.onDataChange(Unknown Source:7)
at com.google.android.gms.internal.to.zza(Unknown Source:13)
at com.google.android.gms.internal.vj.zzHX(Unknown Source:2)
at com.google.android.gms.internal.vp.run(Unknown Source:65)
at android.os.Handler.handleCallback(Handler.java:789)
at android.os.Handler.dispatchMessage(Handler.java:98)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
我要做list.java
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_me_todolist);
Intent intent = getIntent();
student_id = intent.getStringExtra("student_id");
student_name = intent.getStringExtra("student_name");
createTop();
createDetail();
}
private void createDetail() {
final FirebaseDatabase database = FirebaseDatabase.getInstance();
final DatabaseReference hom = database.getReference("Student").child(student_id).child("event");
listview = findViewById(R.id.listview);
final ArrayAdapter adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1,android.R.id.text1);
listview.setAdapter(adapter);
hom.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot event : dataSnapshot.getChildren() ) {
Event = event.getValue().toString();
Log.e("Metodolist",Event);
adapter.add(Event);
adapter.notifyDataSetChanged();
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
Log.e("MeTo list","Pass1");
listview.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, final int position, long id) {
hom.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
Intent intent = new Intent(MeTodolist.this, MeTodolistModify.class);
String title = dataSnapshot.child(Integer.toString(position)).getValue().toString();
Bundle bundle = new Bundle();
bundle.putString("title", title);
bundle.putInt("position",position);
bundle.putString("student_id",student_id);
bundle.putString("student_name",student_name);
intent.putExtras(bundle);
startActivity(intent);
Log.e("CHANGE",title);
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
});
Log.e("Metodolist","pass2");
listview.setOnItemLongClickListener(new
AdapterView.OnItemLongClickListener() {
@Override
public boolean onItemLongClick(AdapterView<?> arg0, View arg1,
final int position, long id) {
hom.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
// String STR= event.getValue().toString();
adapter.getItem(position);
// Log.e("To do List", String.valueOf(position));
adapter.remove(position);
// Log.e("GETUID",event.getUid());
for(position1 = position; position1<listview.getCount();
position1 ++) {
hom.child(Integer.toString(position1)).removeValue();
hom.child(Integer.toString(position1)).setValue(dataSnapshot.child(Integer.toString(position1 + 1)).getValue());
hom.child(Integer.toString(position1 + 1)).removeValue();
adapter.notifyDataSetChanged();
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
return true;
}
});
}
private void createTop() {
title = findViewById(R.id.me_calendar_title);
title.setText(student_name + "todolist");
back = findViewById(R.id.me_calendar_back);
back.setOnClickListener(this);
add = findViewById(R.id.me_calendar_add);
add.setOnClickListener(this);
}
@Override
public void onClick(View view) {
Intent intent;
switch (view.getId()) {
case R.id.me_calendar_back:
intent = new Intent(this, Me.class);
intent.putExtra("student_id", student_id);
startActivity(intent);
break;
case R.id.me_calendar_add:
intent = new Intent(this,MeTodolistAdd.class);
intent.putExtra("student_id",student_id);
intent.putExtra("student_name",student_name);
startActivity(intent);
break;
}
}
}
MeTodolist.java:89位于以下位置：
listview.setOnItemClickListener, String title = dataSnapshot.child(Integer.toString(position)).getValue().toString();