Question

FIREBASE DATABASE

我能够从Firebase读取数据但是当我尝试将值（Item）添加到ArrayList时，该项目为null值..

MainActivity.java

1    package com.example.digesh.divinecart; 
2     
3    import android.os.Bundle; 
4    import android.support.v7.app.AppCompatActivity; 
5    import android.widget.GridView; 
6     
7    import com.firebase.client.ChildEventListener; 
8    import com.firebase.client.DataSnapshot; 
9    import com.firebase.client.Firebase; 
10   import com.firebase.client.FirebaseError; 
11   import com.google.firebase.database.FirebaseDatabase; 
12    
13   import java.util.ArrayList; 
14    
15   public class MainActivity extends AppCompatActivity { 
16    
17       Item i = new Item(); 
18       GridView gridView; 
19       ArrayList<Item> items = new ArrayList<Item>(); 
20       itemAdapter itemadapter; 
21       FirebaseDatabase database; 
22       //DatabaseReference mRef; 
23       Firebase mRef; 
24    
25       @Override 
26       protected void onCreate(Bundle savedInstanceState) { 
27           super.onCreate(savedInstanceState); 
28           setContentView(R.layout.activity_main); 
29           Firebase.setAndroidContext(this); 
30    
31           //mRef = FirebaseDatabase.getInstance().getReference(); 
32    
33           //mRef = database.getReference(); 
34           mRef = new Firebase("https://divinecart-9b58e.firebaseio.com/"); 
35    
36    
37          /* mRef.addValueEventListener(new ValueEventListener() { 
38               @Override 
39               public void onDataChange(DataSnapshot dataSnapshot) { 
40                   itemName = dataSnapshot.getValue(String.class); 
41                   name1 = (TextView)findViewById(R.id.name); 
42                   name1.setText(itemName); 
43    
44               } 
45    
46               @Override 
47               public void onCancelled(FirebaseError firebaseError) { 
48    
49               } 
50           });*/ 
51    
52    
53           gridView = (GridView) findViewById(R.id.gridview); 
54    
55    
56           // itemAdapter itemadapter = new itemAdapter(MainActivity.this,image,itemName,itemPrice); 
57           itemadapter = new itemAdapter(MainActivity.this, getItems()); 
58    
59    
60           gridView.setAdapter(itemadapter); 
61           /*gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
62               @Override 
63               public void onItemClick(AdapterView<?> parent, View view, int position, long l) { 
64                   //String selectedItem = parent.getItemAtPosition(position).toString(); 
65                   Intent i = new Intent(getApplicationContext(),itemdetails.class); 
66                   i.putExtra("Position",position); 
67                   startActivity(i); 
68    
69                   //Toast.makeText(getApplicationContext(),itemName[position],Toast.LENGTH_LONG).show(); 
70                   Toast.makeText(getApplicationContext(),itemName[position],Toast.LENGTH_LONG).show(); 
71    
72               } 
73           });*/ 
74       } 
75    
76       public void fetchData(DataSnapshot ds) { 
77           items.clear(); 
78    
79           for (DataSnapshot data : ds.getChildren()) { 
80               //i = new Item(); 
81               //i = data.getValue(Item.class); 
82               i = (Item) data.getValue(Item.class); 
83               //i = (Item)data.getValue(Item.class); 
84    
85    
86               items.add(i); 
87               //System.out.println(i.getName()); 
88               //items.add(i.getName().toString(),i.getPrice().toString()); 
89           } 
90           itemadapter.notifyDataSetChanged(); 
91    
92       } 
93    
94       public ArrayList<Item> getItems() { 
95           mRef.addChildEventListener(new ChildEventListener() { 
96               @Override 
97               public void onChildAdded(DataSnapshot dataSnapshot, String previousChildName) { 
98    
99                   fetchData(dataSnapshot); 
100                  itemadapter.notifyDataSetChanged(); 
101              } 
102   
103              @Override 
104              public void onChildChanged(DataSnapshot dataSnapshot, String s) { 
105   
106                  fetchData(dataSnapshot); 
107                  itemadapter.notifyDataSetChanged(); 
108   
109              } 
110   
111              @Override 
112              public void onChildRemoved(DataSnapshot dataSnapshot) { 
113   
114              } 
115   
116              @Override 
117              public void onChildMoved(DataSnapshot dataSnapshot, String s) { 
118   
119              } 
120   
121              @Override 
122              public void onCancelled(FirebaseError firebaseError) { 
123   
124              } 
125          }); 
126          return items; 
127      } 
128   
129   
130  } 
131

Item.java

1    package com.example.digesh.divinecart; 
2     
3    import com.fasterxml.jackson.annotation.JsonIgnoreProperties; 
4     
5    /** 
6     * Created by Digesh on 26-10-16. 
7     */ 
8    @JsonIgnoreProperties(ignoreUnknown = true) 
9    public class Item { 
10       //private int image; 
11       private String name; 
12       private String price; 
13    
14       public Item() { 
15    
16    
17       } 
18    
19       public Item(String name, String price){ 
20           //this.image = image; 
21           super(); 
22           this.name = name; 
23           this.price = price; 
24    
25       } 
26    
27    
28    
29       /* public int getImage(){ 
30               return image; 
31           } 
32           public void setImage(int image){ 
33               this.image = image; 
34           } 
35       */ 
36       public String getName(){ 
37           return name; 
38       } 
39       public void setName(String name){ 
40           this.name = name; 
41       } 
42    
43       public String getPrice(){ 
44           return price; 
45       } 
46       public void setPrice(String price){ 
47           this.price = price; 
48       } 
49   } 
50

Answer 1

您似乎最初使用了新的9.x.x SDK，然后将大部分代码注释掉，现在使用的是旧版2.5.x SDK。但是您必须在build.gradle文件中保留对新SDK的引用，例如com.google.firebase.database.FirebaseDatabase，因为您的代码包含id_token的声明。旧版SDK和新SDK不兼容，不能在同一版本中使用。这可能是您正在观察的问题的原因。选择一个SDK或另一个SDK并更新build.gradle和代码以仅使用一个。有关详细信息，请参阅Firebase Upgrade Guide。

Answer 2

您的问题出在您的Item类中。您请求的值必须完全匹配数据库中的值，该类应更改如下

public class Item { 
10       //private int image; 
11       private String itemName; 
12       private String itemPrice; 
13    
14       public Item() { 
15    
16    
17       } 
18    
19       public Item(String itemName, String itemPrice){ 
20           //this.image = image; 
21           super(); 
22           this.itemName = itemName; 
23           this.itemPrice = itemPrice; 
24    
25       } 
26    
27    
28    
29       /* public int getImage(){ 
30               return image; 
31           } 
32           public void setImage(int image){ 
33               this.image = image; 
34           } 
35       */ 
36       public String getItemName(){ 
37           return itemName; 
38       } 
39       public void setName(String name){ 
40           this.itemName = itemName; 
41       } 
42    
43       public String getItemPrice(){ 
44           return itemPrice; 
45       } 
46       public void setItemPrice(String itemPrice){ 
47           this.itemPrice = itemPrice; 
48       } 
49   }

这应该使数据快照起作用。当该Item Class从数据库中提取数据时，名称必须完全相同，以便知道要拉什么。

我能够检索Firebase数据但无法添加到ArrayList

2 个答案: