public class MainActivity extends AppCompatActivity {
        private FirebaseAnalytics mFirebaseAnalytics;
        private FirebaseAuth mFirebaseAuth;
        private DatabaseReference mPicDataReference;
        private FirebaseStorage mFirebaseStorage;
        private Button button;
        private ImageView imageView;
        private ProgressBar progressBar;
        private GridView gridView;
        private ArrayList<PictureItem> pictureItems;


        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            //連結畫面
            button = findViewById(R.id.button2);
            imageView = findViewById(R.id.imageView);
            progressBar = findViewById(R.id.progressBar2);
            progressBar.setVisibility(View.INVISIBLE);//ProgressBar設為不可見
            gridView = findViewById(R.id.gridView);
            pictureItems = new ArrayList<>();

            // Obtain the FirebaseAnalytics instance.
            mFirebaseAnalytics = FirebaseAnalytics.getInstance(this);
            mFirebaseAuth = FirebaseAuth.getInstance();
            mPicDataReference = FirebaseDatabase.getInstance().getReference().child("pic");
            mFirebaseStorage = FirebaseStorage.getInstance();
            //匿名登入
            mFirebaseAuth.signInAnonymously();
            //取得firebase database 的照片檔案路徑後，顯示擴充到gridView
            mPicDataReference.addChildEventListener(new ChildEventListener() {
                @Override
                public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
                    String path = dataSnapshot.child("path").getValue().toString();
                    PictureItem pictureItem = new PictureItem(path);
                    pictureItems.add(pictureItem);
                    MyPictureListAdapter myPictureListAdapter = new MyPictureListAdapter();
                    myPictureListAdapter.pictureItems = pictureItems;
                    gridView.setAdapter(myPictureListAdapter);
                }

                @Override
                public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

                }

                @Override
                public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {

                }

                @Override
                public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

                }

                @Override
                public void onCancelled(@NonNull DatabaseError databaseError) {

                }
            });
            //擷取照片按鈕監聽器
            button.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Intent intent = new Intent();
                    intent.setType("image/*");//開啟Pictures畫面Type設定為image
                    intent.setAction(Intent.ACTION_GET_CONTENT);//使用Intent.ACTION_GET_CONTENT這個Action
                    startActivityForResult(intent, 0);//取得照片後返回此畫面
                }
            });
        }

        @Override
        protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
            //當使用者按下確定後
            if(resultCode == RESULT_OK){
                //取得圖檔的路徑位置

                Uri uri = data.getData();
                //抽象資料的接口
                ContentResolver cr = this.getContentResolver();
                try {//由抽象資料接口轉換圖檔路徑為Bitmap

                    final Bitmap bitmap = BitmapFactory.decodeStream(cr.openInputStream(uri));
                    //使用UUID為上傳檔名
                    String fileName = UUID.randomUUID().toString() + ".jpg";
                    //壓縮bitmap到ByteArrayOutputStream baos
                    ByteArrayOutputStream baos = new ByteArrayOutputStream();
                    bitmap.compress(Bitmap.CompressFormat.JPEG, 50, baos);
                    //設定bitmap到imageView
                    imageView.setImageBitmap(bitmap);
                    //帶有bitmap的ByteArrayOutputStream baos 轉成byte[]
                    byte[] imageData = baos.toByteArray();
                    //建立上傳圖片的metadata
                    StorageMetadata storageMetadata = new StorageMetadata
                            .Builder().setCustomMetadata("MyKey", "MyValue").build();
                    //參考到firebase storage的/pic/uid/fileName位址
                    final StorageReference mountainsRef = mFirebaseStorage.getReference()
                            .child("pic")
                            .child(mFirebaseAuth.getCurrentUser().getUid())
                            .child(fileName);
                    //用byte[]上傳圖檔到firebase storage
                    UploadTask uploadTask = mountainsRef.putBytes(imageData, storageMetadata);
                    //把上傳進度條設為顯示
                    progressBar.setVisibility(View.VISIBLE);
                    //上傳圖片到firebase storage的監聽器設定
                    uploadTask.addOnFailureListener(new OnFailureListener() {
                        @Override//上傳失敗執行
                        public void onFailure(@NonNull Exception e) {
                            Toast.makeText(MainActivity.this, "上傳失敗", Toast.LENGTH_LONG).show();
                            progressBar.setVisibility(View.INVISIBLE);
                        }
                    }).addOnSuccessListener(new OnSuccessListener<UploadTask.TaskSnapshot>() {
                        @Override//上傳成功執行
                        public void onSuccess(UploadTask.TaskSnapshot taskSnapshot) {
                            Toast.makeText(MainActivity.this, "上傳成功", Toast.LENGTH_LONG).show();
                            //把上傳此照片的uid、下載路徑、檔案路徑記錄到Firebase Database/pic/自動key/
                            HashMap<String, String> picData = new HashMap<>();
                            picData.put("uid", mFirebaseAuth.getCurrentUser().getUid());
                            picData.put("link", mountainsRef.getDownloadUrl().toString());
                            picData.put("path", mountainsRef.getPath());
                            mPicDataReference.push().setValue(picData);
                            //隱藏上傳進度條
                            progressBar.setVisibility(View.INVISIBLE);
                        }
                    }).addOnProgressListener(new OnProgressListener<UploadTask.TaskSnapshot>() {
                        @Override//正在上傳圖片時顯示進度bar
                        public void onProgress(UploadTask.TaskSnapshot taskSnapshot) {
                            int progressPercentage = (int) ((taskSnapshot.getBytesTransferred() * 100)
                                    / (taskSnapshot.getTotalByteCount()));
                            Log.d("uploading", progressPercentage+"%");
                            progressBar.setProgress(progressPercentage);
                        }
                    });


                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                }
            }
            super.onActivityResult(requestCode, resultCode, data);
        }
        //Gird View 用的 Adapter
        private class MyPictureListAdapter extends BaseAdapter {
            ArrayList<PictureItem> pictureItems;

            @Override
            public int getCount() {
                return pictureItems.size();
            }

            @Override
            public PictureItem getItem(int position) {
                return pictureItems.get(position);
            }

            @Override
            public long getItemId(int position) {
                return position;
            }

            @Override
            public View getView(int position, View convertView, ViewGroup parent) {
                LayoutInflater mInflater = getLayoutInflater();
                View myView = mInflater.inflate(R.layout.image_grid, null);
                final PictureItem pictureItem = pictureItems.get(position);
                ImageView imageView = (ImageView)myView.findViewById(R.id.imageView2);
                //使用 FirebaseUI 下載圖片
                Glide.with(MainActivity.this)
                        .load(mFirebaseStorage.getReference().child(pictureItem.imagePath))
                        .into(imageView);
                return myView;
            }
        }


    }