Question

我是Android开发的新手我接下来通过Picasso加载图像的一些教程，但是我有一个问题，就像我从firebase存储通过Picasso加载图像时出现的图像但是当我关闭我的应用程序并打开应用程序时图像消失了，我需要再次上传和检索它。我的朋友建议我将图像存储在缓存中，所以请帮我这样做。这是我为从firebase存储加载图像而实现的代码。

import android.app.ProgressDialog;
import android.content.Intent;
import android.graphics.Bitmap;
import android.net.Uri;
import android.provider.MediaStore;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;

import com.google.android.gms.tasks.OnFailureListener;
import com.google.android.gms.tasks.OnSuccessListener;
import com.google.firebase.storage.FirebaseStorage;
import com.google.firebase.storage.OnProgressListener;
import com.google.firebase.storage.StorageReference;
import com.google.firebase.storage.UploadTask;
import com.squareup.picasso.Picasso;

import java.io.IOException;

import static android.R.attr.bitmap;

public class ProfilePhotoUI extends AppCompatActivity implements View.OnClickListener /*  implementing click listener */ {
    //a constant to track the file chooser intent
    private static final int PICK_IMAGE_REQUEST = 234;

    //Buttons
    private Button buttonChoose;
    private Button buttonUpload;

    //ImageView
    private ImageView imageView;

    //a Uri object to store file path
    private Uri filePath;

    //firebase storage reference
    private StorageReference storageReference;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_profile_photo_ui);

        //getting views from layout
        buttonChoose = (Button) findViewById(R.id.buttonChoose);
        buttonUpload = (Button) findViewById(R.id.buttonUpload);

        imageView = (ImageView) findViewById(R.id.imageView);

        //attaching listener
        buttonChoose.setOnClickListener(this);
        buttonUpload.setOnClickListener(this);

        //getting firebase storage reference
        storageReference = FirebaseStorage.getInstance().getReference();
    }

    //method to show file chooser
    private void showFileChooser() {
        Intent intent = new Intent();
        intent.setType("image/*");
        intent.setAction(Intent.ACTION_GET_CONTENT);
        startActivityForResult(Intent.createChooser(intent, "Select Picture"), PICK_IMAGE_REQUEST);
    }

    //handling the image chooser activity result
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == PICK_IMAGE_REQUEST && resultCode == RESULT_OK && data != null && data.getData() != null) {
            filePath = data.getData();
            try {
                Bitmap bitmap = MediaStore.Images.Media.getBitmap(getContentResolver(), filePath);
                imageView.setImageBitmap(bitmap);

            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    //this method will upload the file
    private void uploadFile() {
        //if there is a file to upload
        if (filePath != null) {
            //displaying a progress dialog while upload is going on
            final ProgressDialog progressDialog = new ProgressDialog(this);
            progressDialog.setTitle("Uploading");
            progressDialog.show();

            StorageReference riversRef = storageReference.child("images/pic.jpg");
            riversRef.putFile(filePath)
                    .addOnSuccessListener(new OnSuccessListener<UploadTask.TaskSnapshot>() {
                        @Override
                        public void onSuccess(UploadTask.TaskSnapshot taskSnapshot) {
                            //if the upload is successfull
                            //hiding the progress dialog
                            progressDialog.dismiss();
                            Uri downloadUri = taskSnapshot.getDownloadUrl();

                            Picasso.with(ProfilePhotoUI.this).load(downloadUri).transform(new CircleTransform()).into(imageView);


                            //and displaying a success toast
                            Toast.makeText(getApplicationContext(), "File Uploaded ", Toast.LENGTH_LONG).show();

                        }
                    })
                    .addOnFailureListener(new OnFailureListener() {
                        @Override
                        public void onFailure(@NonNull Exception exception) {
                            //if the upload is not successfull
                            //hiding the progress dialog
                            progressDialog.dismiss();

                            //and displaying error message
                            Toast.makeText(getApplicationContext(), exception.getMessage(), Toast.LENGTH_LONG).show();
                        }
                    })
                    .addOnProgressListener(new OnProgressListener<UploadTask.TaskSnapshot>() {
                        @Override
                        public void onProgress(UploadTask.TaskSnapshot taskSnapshot) {
                            //calculating progress percentage
                            double progress = (100.0 * taskSnapshot.getBytesTransferred()) / taskSnapshot.getTotalByteCount();

                            //displaying percentage in progress dialog
                            progressDialog.setMessage("Uploaded " + ((int) progress) + "%...");
                        }
                    });
        }
        //if there is not any file
        else {
            //you can display an error toast
        }
    }

    @Override
    public void onClick(View view) {
        //if the clicked button is choose
        if (view == buttonChoose) {
            showFileChooser();
        }
        //if the clicked button is upload
        else if (view == buttonUpload) {
            uploadFile();
        }
    }
}

Answer 1

我通常会看到人们在Firebase Database中保存 DownloadUrl 变量，但是您也可以将其保存在SQL数据库中。

保存 DownloadUrl 的任何地方，都可以在Picasso中使用它，如下所示：

Picasso.with(getActivity())
.load(imageUrl)
.networkPolicy(NetworkPolicy.OFFLINE)
.into(imageView, new Callback() {
    @Override
    public void onSuccess() {

    }

    @Override
    public void onError() {
        //Try again online if cache failed
        Picasso.with(getActivity())
                .load(posts.get(position).getImageUrl())
                .error(R.drawable.header)
                .into(imageView, new Callback() {
            @Override
            public void onSuccess() {

            }

            @Override
            public void onError() {
                Log.v("Picasso","Could not fetch image");
            }
        });
    }
});

networkPolicy(NetworkPolicy.OFFLINE)将迫使Picasso首先在硬盘上查找它。如果存在清除缓存，Picasso将在线查找。

Picasso会将您的图片保存在以下路径（例如仿真器）中：

/data/data/com.example.myapp/cache/picasso-cache

Picasso一旦将图像保存在缓存中，我不知道如何在不使用Picasso的情况下访问图像。

您还可以使用DownloadManager将图像下载到缓存目录中。其中（字符串）destinationDirectory = getContext().getCacheDir().getPath().toString()

private void downloadFile(Context context, final String fileName, final String fileExtension, String destinationDirectory, String url) {

        BroadcastReceiver onComplete;

        DownloadManager downloadManager = (DownloadManager) context.getSystemService(Context.DOWNLOAD_SERVICE);

        Uri uri = Uri.parse(url);

        DownloadManager.Request request = new DownloadManager.Request(uri);

        request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
        request.setDestinationUri(Uri.fromFile(new File(destinationDirectory,fileName + fileExtension)));
        request.setAllowedNetworkTypes(DownloadManager.Request.NETWORK_WIFI | DownloadManager.Request.NETWORK_MOBILE);

        onComplete = new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                String action = intent.getAction();
                if (DownloadManager.ACTION_DOWNLOAD_COMPLETE.equals(action)) {

                    //DO WHATEVER YOU NEED AFTER FILE HAS BEEN DOWNLOADED HERE

                }

            }
        };

        getActivity().registerReceiver(onComplete, new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE));

        downloadManager.enqueue(request);


    }

下载图像后，您必须保存新的 ImagePath 。希望对您有所帮助！

如何在我的应用程序的缓存中通过picasso保存从firebase存储加载的图像

1 个答案: