如何解决;尝试调用虚拟方法';java.lang.String java.lang.Object.toString()';在空对象引用上;?
我正在尝试修复过去24小时内出现的空指针异常问题。它在如何解决;尝试调用虚拟方法';java.lang.String java.lang.Object.toString()';在空对象引用上;?,java,android,firebase,Java,Android,Firebase,我正在尝试修复过去24小时内出现的空指针异常问题。它在getOppositeSexUsers()中不断显示错误。我问了一些问题,也得到了回复,但每次都显示空指针异常 这是logcat java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference at com.tec
getOppositeSexUsers()
中不断显示错误。我问了一些问题,也得到了回复,但每次都显示空指针异常
这是logcat
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
at com.techjd.hubu.MainActivity$6.onChildAdded(MainActivity.java:205)
at com.google.firebase.database.core.ChildEventRegistration.fireEvent(com.google.firebase:firebase-database@@19.2.0:79)
at com.google.firebase.database.core.view.DataEvent.fire(com.google.firebase:firebase-database@@19.2.0:63)
at com.google.firebase.database.core.view.EventRaiser$1.run(com.google.firebase:firebase-database@@19.2.0:55)
at android.os.Handler.handleCallback(Handler.java:815)
at android.os.Handler.dispatchMessage(Handler.java:104)
at android.os.Looper.loop(Looper.java:207)
at android.app.ActivityThread.main(ActivityThread.java:5740)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:905)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:766)
这是主要的活动代码
public void getOppositeSexUsers(){
DatabaseReference oppositeSexDb = FirebaseDatabase.getInstance().getReference().child("Users").child(oppositeUserSex);
oppositeSexDb.addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(@NonNull DataSnapshot dataSnapshot, String s) {
if (dataSnapshot.exists() && !dataSnapshot.child("connections").child("nope").hasChild(currentUId) && !dataSnapshot.child("connections").child("yes").hasChild(currentUId)){
Object ImageData = dataSnapshot.child("profileImageUrl").getValue();
String ImageDefault = "default";
if (ImageData != null){
ImageDefault = ImageData.toString();
}
cards item = new cards(dataSnapshot.getKey(), dataSnapshot.child("Name").getValue().toString() , ImageDefault);
//cards item = new cards(dataSnapshot.getKey(), dataSnapshot.child("Name").getValue().toString(), dataSnapshot.child("profileImageUrl").getValue().toString());
rowItems.add(item);
arrayAdapter.notifyDataSetChanged();
}
}
@Override
public void onChildChanged(@NonNull DataSnapshot dataSnapshot, String s) {
}
@Override
public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {
}
@Override
public void onChildMoved(@NonNull DataSnapshot dataSnapshot, String s) {
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
每次我在GetOppositesXUsers()中尝试解决方案时,它都会生成空指针异常。修复方法是什么?要避免此
异常
请在名称数据
中检查null
,就像对图像数据
所做的那样
@Override
public void onChildAdded(@NonNull DataSnapshot dataSnapshot, String s) {
if (dataSnapshot.exists() && !dataSnapshot.child("connections").child("nope").hasChild(currentUId) && !dataSnapshot.child("connections").child("yes").hasChild(currentUId)){
Object ImageData = dataSnapshot.child("profileImageUrl").getValue();
String ImageDefault = "default";
if (ImageData != null){
ImageDefault = ImageData.toString();
}
// here check your name properity is null or not like below
String nameDataDefault = "default";
Object nameData = dataSnapshot.child("Name").getValue(); // check key is Name or name.
if (nameData != null){
nameDataDefault = nameData.toString();
}
cards item = new cards(dataSnapshot.getKey(), nameDataDefault, ImageDefault);
//cards item = new cards(dataSnapshot.getKey(), dataSnapshot.child("Name").getValue().toString(), dataSnapshot.child("profileImageUrl").getValue().toString());
rowItems.add(item);
arrayAdapter.notifyDataSetChanged();
}
}
四次。@AshvinSharmaCan我能得到你的电子邮件地址吗?