无法解析 Firebase 中的符号 storageRef

Question

我正在使用 fire base 存储图像，我在存储中遇到错误 Ref 无法解析符号，请帮助。

public class Sample extends Activity {
public static final String GridViewDemo_ImagePath = Environment.getExternalStorageDirectory().getAbsolutePath() + "/Pencilrulerlearner/";
StorageReference riversRef;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    File targetDirector = new File(GridViewDemo_ImagePath);
    File[] files = targetDirector.listFiles();
    for (File file1 : files) {
        Uri file= Uri.fromFile(file1);


        storageRef.child("images/" + file.getLastPathSegment());
      UploadTask  uploadTask = riversRef.putFile(file);


        uploadTask.addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception exception) {
                // Handle unsuccessful uploads
            }
        }).addOnSuccessListener(new OnSuccessListener<UploadTask.TaskSnapshot>() {
            @Override
            public void onSuccess(UploadTask.TaskSnapshot taskSnapshot) {
                // taskSnapshot.getMetadata() contains file metadata such as size, content-type, and download URL.
                Uri downloadUrl = taskSnapshot.getDownloadUrl();
            }
        });
    }

}
}

即使我将 storageRef 更改为riversRef ，我也会收到以下错误

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.firebase.storage.StorageReference com.google.firebase.storage.StorageReference.child(java.lang.String)' on a null object reference
        at nidhinkumar.firebaseexample.Sample.onCreate(Sample.java:31)
        at android.app.Activity.performCreate(Activity.java:6092)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1112)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2468)

            

Answer 1

变量storageRef未初始化。

首先，创建一个FirebaseStorage变量：

storage = FirebaseStorage.getInstance();

然后像这样初始化StorageReference类型变量storageRef：

storageRef = storage.getReference();

Answer 2

做一件简单的事导入这个文件

import com.google.firebase.storage.StorageReference;

欢迎您:)

Answer 3

您收到此错误是因为 storageRef 变量尚未初始化。任何在 null 引用上调用方法的尝试都将导致 java.lang.NullPointerException。

在您的情况下，您应该首先获得对 FirebaseStorage 实例的引用：

FirebaseStorage storage = FirebaseStorage.getInstance();

然后，您可以通过getReferenceFromUrl 方法获得对所需存储的引用。

StorageReference storageRef = storage.getReferenceFromUrl("Url to storage");

以下storageRef已初始化，可以使用了。