我在从 Firestore 获取数据时遇到问题,在 Java 代码中我们可以这样做:
DocumentReference docRef = db.collection("cities").document("SF");
docRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
@Override
public void onComplete(@NonNull Task<DocumentSnapshot> task) {
if (task.isSuccessful()) {
DocumentSnapshot document = task.getResult();
if (document != null) {
Log.d(TAG, "DocumentSnapshot data: " + task.getResult().getData());
} else {
Log.d(TAG, "No such document");
}
} else {
Log.d(TAG, "get failed with ", task.getException());
}
}
});
但在 Kotlin 中,当我尝试覆盖 onComplete
函数时,它不可用。那么,我怎样才能得到“任务”呢?
最佳答案
如果您使用的是 Android Studio 3,您可以使用它来 convert Java code to Kotlin .将感兴趣的代码放入 java 文件中,然后从菜单栏中选择代码 > 将 Java 文件转换为 Kotlin 文件。
例如,对于您发布的这段代码,转换结果如下所示:
import android.support.annotation.NonNull;
import android.util.Log;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.firestore.DocumentReference;
import com.google.firebase.firestore.DocumentSnapshot;
import com.google.firebase.firestore.FirebaseFirestore;
public class ConversionExample {
private static final String TAG = "ConversionExample";
public void getDoc() {
FirebaseFirestore db = FirebaseFirestore.getInstance();
DocumentReference docRef = db.collection("cities").document("SF");
docRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
@Override
public void onComplete(@NonNull Task<DocumentSnapshot> task) {
if (task.isSuccessful()) {
DocumentSnapshot document = task.getResult();
if (document != null) {
Log.d(TAG, "DocumentSnapshot data: " + task.getResult().getData());
} else {
Log.d(TAG, "No such document");
}
} else {
Log.d(TAG, "get failed with ", task.getException());
}
}
});
}
}
转换为 Kotlin 的文件:
import android.util.Log
import com.google.firebase.firestore.FirebaseFirestore
class ConversionExample {
fun getDoc() {
val db = FirebaseFirestore.getInstance()
val docRef = db.collection("cities").document("SF")
docRef.get().addOnCompleteListener { task ->
if (task.isSuccessful) {
val document = task.result
if (document != null) {
Log.d(TAG, "DocumentSnapshot data: " + task.result.data)
} else {
Log.d(TAG, "No such document")
}
} else {
Log.d(TAG, "get failed with ", task.exception)
}
}
}
companion object {
private val TAG = "ConversionExample"
}
}
关于android - Kotlin - 如何执行 onCompleteListener 以从 Firestore 获取数据?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/47214368/