如何使用Firebase数据填充Spinner？
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我已经在SO上的线程上搜索了关于线程的文章，试图弄清楚我是如何做到这一点的，但是还没有更接近。
这个线程（How to get a String List from Firebase to fill a Spinner）似乎可能是有益的，但是我不确定如何为我自己的场景实现它。
我希望属性地址出现在微调器中。
如果问题看起来含糊不清，很难解释。
MaintenanceActivity
public class MaintenanceActivity extends AppCompatActivity {
EditText editTextTitle;
EditText editTextDesc;
Spinner spinnerPrimary;
Spinner spinnerSecondary;
Spinner spinnerProperty;
Button buttonSubmit;
DatabaseReference databaseMaintenance;
ListView listViewIssues;
List<Maintenance> maintenanceList;
fDatabaseRoot.child("propertyAddress").addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
// Is better to use a List, because you don't know the size
// of the iterator returned by dataSnapshot.getChildren() to
// initialize the array
final List<String> propertyAddress = new ArrayList<String>();
for (DataSnapshot addressSnapshot: dataSnapshot.getChildren()) {
String propertyAddress = addressSnapshot.child("propertyAddress").getValue(String.class);
propertyAddress.add(propertyAddress);
}
Spinner spinnerProperty = (Spinner) findViewById(R.id.spinnerProperty);
ArrayAdapter<String> addressAdapter = new ArrayAdapter<String>(MaintenanceActivity.this, android.R.layout.simple_spinner_item, areas);
addressAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinnerProperty.setAdapter(addressAdapter);
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
activity_maintenance
<Spinner
android:id="@+id/spinnerProperty"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:entries="@array/fuel" />
Firebase数据库
错误
用这个答案得到几个错误。我以前遇到过这些错误，不知道如何解决它们。
LogCat错误
03-01 17:19:53.402 28517-28517/com.example.***.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.***.myapplication, PID: 28517
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:445)
at android.widget.ArrayAdapter.getDropDownView(ArrayAdapter.java:493)
at android.widget.Spinner$DropDownAdapter.getDropDownView(Spinner.java:994)
at android.widget.Spinner$DropDownAdapter.getView(Spinner.java:990)
at android.widget.Spinner.measureContentWidth(Spinner.java:856)
at android.widget.Spinner$DropdownPopup.computeContentWidth(Spinner.java:1225)
at android.widget.Spinner$DropdownPopup.show(Spinner.java:1251)
at android.widget.Spinner.performClick(Spinner.java:780)
at android.support.v7.widget.AppCompatSpinner.performClick(AppCompatSpinner.java:442)
at android.view.View$PerformClick.run(View.java:24770)
at android.os.Handler.handleCallback(Handler.java:790)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6494)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
03-01 17:19:53.403 28517-28517/com.example.***.myapplication E/UncaughtException: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:445)
at android.widget.ArrayAdapter.getDropDownView(ArrayAdapter.java:493)
at android.widget.Spinner$DropDownAdapter.getDropDownView(Spinner.java:994)
at android.widget.Spinner$DropDownAdapter.getView(Spinner.java:990)
at android.widget.Spinner.measureContentWidth(Spinner.java:856)
at android.widget.Spinner$DropdownPopup.computeContentWidth(Spinner.java:1225)
at android.widget.Spinner$DropdownPopup.show(Spinner.java:1251)
at android.widget.Spinner.performClick(Spinner.java:780)
at android.support.v7.widget.AppCompatSpinner.performClick(AppCompatSpinner.java:442)
at android.view.View$PerformClick.run(View.java:24770)
at android.os.Handler.handleCallback(Handler.java:790)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6494)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
答案
我可以帮助你，但你需要配置数据库和firebase，请参阅docs。
在你的活动之后：
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference fDatabaseRoot = database.getReference();
fDatabaseRoot.child("properties").addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
// Is better to use a List, because you don't know the size
// of the iterator returned by dataSnapshot.getChildren() to
// initialize the array
final List<String> propertyAddressList = new ArrayList<String>();
for (DataSnapshot addressSnapshot: dataSnapshot.getChildren()) {
String propertyAddress = addressSnapshot.child("propertyAddress").getValue(String.class);
if (propertyAddress!=null){
propertyAddressList.add(propertyAddress);
}
}
Spinner spinnerProperty = (Spinner) findViewById(R.id.maintenanceProperty);
ArrayAdapter<String> addressAdapter = new ArrayAdapter<String>(MaintenanceActivity.this, android.R.layout.simple_spinner_item, propertyAddressList);
addressAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinnerProperty.setAdapter(addressAdapter);
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
您已经为propertyAddress添加了一个侦听器，但是当数据快照返回时，您再次探测propertyAddress，这将无法工作，因为侦听器已经返回了属性地址。我上面写的方式将返回数据库中的所有键，在每个键中都有一个可以检索的propertyAddress。试试看。
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