如何從偵聽器方法返回變量

-2

在下面的代碼中，我聲明瞭稍後在方法ImageLoad中設置的類變量downloadUrl。我試圖設置變量並在調用方法時返回它。但是我看到變量返回null。這裏發生了什麼？我如何正確地返回這個變量？如何從偵聽器方法返回變量

public class ImageActions { 

private Uri downloadUrl; 

public Uri ImageLoad() 
{ 
    FirebaseStorage storage = FirebaseStorage.getInstance(); 
    StorageReference storageRef = storage.getReferenceFromUrl("gs://apptest.appspot.com"); 

    Uri file = Uri.fromFile(new File("sdcard/DCIM/Camera/1466831822883.jpg")); 

    StorageMetadata metadata = new StorageMetadata.Builder().setContentType("image/jpeg").build(); 

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

    uploadTask.addOnProgressListener(new OnProgressListener<UploadTask.TaskSnapshot>() { 
     @Override 
     public void onProgress(UploadTask.TaskSnapshot taskSnapshot) { 
      double progress = (100.0 * taskSnapshot.getBytesTransferred())/taskSnapshot.getTotalByteCount(); 
      System.out.println("Upload is " + progress + "% done"); 
     } 
    }).addOnPausedListener(new OnPausedListener<UploadTask.TaskSnapshot>() { 
     @Override 
     public void onPaused(UploadTask.TaskSnapshot taskSnapshot) { 
      System.out.println("Upload is paused"); 
     } 
    }).addOnFailureListener(new OnFailureListener() { 
     @Override 
     public void onFailure(@NonNull Exception exception) { 
      // Handle unsuccessful uploads 
      System.out.println("Upload failed"); 
     } 
    }).addOnSuccessListener(new OnSuccessListener<UploadTask.TaskSnapshot>() { 
     @Override 
     public void onSuccess(UploadTask.TaskSnapshot taskSnapshot) { 
      // Handle successful uploads on complete 
      downloadUrl = taskSnapshot.getMetadata().getDownloadUrl(); 
      System.out.println("beforeReturn" + downloadUrl); //This prints correct (non-null) value 
      System.out.println("Upload completed");     
     } 
    }); 

    System.out.println("beforeReturn" + downloadUrl); //This prints null 

    return downloadUrl; 

} 
}

來源

2016-09-18 dacscan3669

它將爲空，因爲上傳任務是異步的，並且你得到null的語句在'onSuccess'之前執行，就像在你開始'uploadtask'後執行S.O.P語句一樣。你可以通過自己的界面來返回url，這將是最好的。 –

如下你可以這樣做：

public class ImageActions { 

public interface OntaskCompleted{ 
    void onSuccess(Uri returnurl); 
    void onfail(); 
} 

private Uri downloadUrl; 

public void ImageLoad(final OntaskCompleted listener) 
{ 
    FirebaseStorage storage = FirebaseStorage.getInstance(); 
    StorageReference storageRef = storage.getReferenceFromUrl("gs://apptest.appspot.com"); 

    Uri file = Uri.fromFile(new File("sdcard/DCIM/Camera/1466831822883.jpg")); 

    StorageMetadata metadata = new StorageMetadata.Builder().setContentType("image/jpeg").build(); 

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

    uploadTask.addOnProgressListener(new OnProgressListener<UploadTask.TaskSnapshot>() { 
     @Override 
     public void onProgress(UploadTask.TaskSnapshot taskSnapshot) { 

     } 
    }).addOnPausedListener(new OnPausedListener<UploadTask.TaskSnapshot>() { 
     @Override 
     public void onPaused(UploadTask.TaskSnapshot taskSnapshot) { 
      System.out.println("Upload is paused"); 
     } 
    }).addOnFailureListener(new OnFailureListener() { 
     @Override 
     public void onFailure(@NonNull Exception exception) { 
      // Handle unsuccessful uploads 
      listener.onfail(); 
     } 
    }).addOnSuccessListener(new OnSuccessListener<UploadTask.TaskSnapshot>() { 
     @Override 
     public void onSuccess(UploadTask.TaskSnapshot taskSnapshot) { 
      // Handle successful uploads on complete 
      downloadUrl = taskSnapshot.getMetadata().getDownloadUrl(); 
        System.out.println("Upload completed"); 
      listenr.onSuccess(downloadurl)    
     } 
    }); 

} 
}

現在調用這個函數如下：

ImageLoadObject.ImageLoad(new OntaskCompleted(){ 

    @Override 
    void onSuccess(Uri url){ 
     //Here you will get the url after upload complete 
    } 
    @Override 
    void onFail(){ 

    } 
});

希望這有助於你。

來源

2016-09-18 05:57:09

謝謝。這有助於。 – dacscan3669

如何從偵聽器方法返回變量

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