Question

我正在使用fire base来存储图像，因为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

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方法获得所需存储的引用。

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

以下storageRef已经启动并可以使用。

Answer 2

导入该文件很简单

import com.google.firebase.storage.StorageReference;

您的欢迎：）

Answer 3

变量"build": "react-scripts build && cp build/index.html build/404.html",未初始化。

首先，创建一个storageRef变量：

FirebaseStorage

然后像这样初始化storage = FirebaseStorage.getInstance();类型变量StorageReference：

storageRef

无法解析firebase中的符号storageRef

3 个答案: