蛋疼的Android BaseAdapter

蛋疼的Android BaseAdapter
```
 1 package com.moniter.helperclasses;
 2 
 3 import java.util.List;
 4 
 5 import android.content.Context;
 6 import android.view.LayoutInflater;
 7 import android.view.View;
 8 import android.view.ViewGroup;
 9 import android.widget.BaseAdapter;
10 import android.widget.ImageView;
11 import android.widget.TextView;
12 
13 import com.hanvon.moniter.R;
14 
15 public class SiteListAdapter extends BaseAdapter {
16 
17     // 地点列表
18     private List<SiteInformation> sites = null;
19     private LayoutInflater mInflater;
20 
21     // Constructor
22     public SiteListAdapter(Context context, List<SiteInformation> sites) {
23         this.sites = sites;
24         this.mInflater = LayoutInflater.from(context);
25     }
26 
27     // 返回列表项数
28     @Override
29     public int getCount() {
30         return sites.size();
31     }
32 
33     @Override
34     public Object getItem(int position) {
35         return sites.get(position);
36     }
37 
38     @Override
39     public long getItemId(int position) {
40         return position;
41     }
42 
43     @SuppressWarnings("null")
44     @Override
45     public View getView(int position, View convertView, ViewGroup parent) {
46         // 取得位置position对应的site信息
47         SiteInformation siteInfo = sites.get(position);
48 
49         //取得ListView的布局文件
50         convertView = mInflater.inflate(R.layout.site_list_item, null);
51         
52         //初始化viewHolder
53         ViewHolder viewHolder = null;
54         
55         //View的绑定
56         if (convertView == null) {
57             viewHolder = new ViewHolder();
58             viewHolder.site_name = (TextView) convertView
59                     .findViewById(R.id.name_site);
60             viewHolder.value_noise = (TextView) convertView
61                     .findViewById(R.id.noise);
62             viewHolder.value_dust = (TextView) convertView
63                     .findViewById(R.id.dust);
64             viewHolder.status_noise = (ImageView) convertView
65                     .findViewById(R.id.color_indicator_noise);
66             viewHolder.status_dust = (ImageView) convertView
67                     .findViewById(R.id.color_indicator_dust);
68             
69             convertView.setTag(viewHolder);
70         } else {
71             viewHolder = (ViewHolder) convertView.getTag();
72         }
73 
74         //取得相应的值：抱错！！！！！为什么？？？？
75         viewHolder.site_name.setText("123");  //???siteInfo.getSiteName()
76         viewHolder.value_noise.setText(siteInfo.getNoiseValue());
77         viewHolder.value_dust.setText(siteInfo.getDustValue());
78         viewHolder.status_noise.setBackgroundResource(siteInfo.getNoiseStatus());
79         viewHolder.status_dust.setBackgroundResource(siteInfo.getDustStatus());
80         
81         //返回Poistion对应的view
82         return convertView;
83     }
84     
85     static class ViewHolder {
86         public TextView site_name;
87         public TextView value_noise;
88         public TextView value_dust;
89         public ImageView status_noise;
90         public ImageView status_dust;
91     }
92 }
```
老是在第75行报错。搞了一天了没有发现原因。

06-16 18:09:50.232: E/AndroidRuntime(10487): FATAL EXCEPTION: main
06-16 18:09:50.232: E/AndroidRuntime(10487): java.lang.NullPointerException
06-16 18:09:50.232: E/AndroidRuntime(10487): at com.moniter.helperclasses.SiteListAdapter.getView(SiteListAdapter.java:75)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.AbsListView.obtainView(AbsListView.java:2040)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.ListView.makeAndAddView(ListView.java:1772)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.ListView.fillDown(ListView.java:672)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.ListView.fillFromTop(ListView.java:732)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.ListView.layoutChildren(ListView.java:1625)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.AbsListView.onLayout(AbsListView.java:1870)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.view.View.layout(View.java:11418)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.view.ViewGroup.layout(ViewGroup.java:4328)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1652)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1510)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.LinearLayout.onLayout(LinearLayout.java:1415)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.view.View.layout(View.java:11418)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.view.ViewGroup.layout(ViewGroup.java:4328)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1652)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1510)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.LinearLayout.onLayout(LinearLayout.java:1415)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.view.View.layout(View.java:11418)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.view.ViewGroup.layout(ViewGroup.java:4328)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1652)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1510)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.LinearLayout.onLayout(LinearLayout.java:1415)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.view.View.layout(View.java:11418)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.view.ViewGroup.layout(ViewGroup.java:4328)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.RelativeLayout.onLayout(RelativeLayout.java:930)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.view.View.layout(View.java:11418)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.view.ViewGroup.layout(ViewGroup.java:4328)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.FrameLayout.onLayout(FrameLayout.java:443)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.view.View.layout(View.java:11418)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.view.ViewGroup.layout(ViewGroup.java:4328)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1652)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1510)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.LinearLayout.onLayout(LinearLayout.java:1415)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.view.View.layout(View.java:11418)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.view.ViewGroup.layout(ViewGroup.java:4328)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.widget.FrameLayout.onLayout(FrameLayout.java:443)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.view.View.layout(View.java:11418)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.view.ViewGroup.layout(ViewGroup.java:4328)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1489)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2442)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.os.Handler.dispatchMessage(Handler.java:99)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.os.Looper.loop(Looper.java:137)
06-16 18:09:50.232: E/AndroidRuntime(10487): at android.app.ActivityThread.main(ActivityThread.java:4441)
06-16 18:09:50.232: E/AndroidRuntime(10487): at java.lang.reflect.Method.invokeNative(Native Method)
06-16 18:09:50.232: E/AndroidRuntime(10487): at java.lang.reflect.Method.invoke(Method.java:511)
06-16 18:09:50.232: E/AndroidRuntime(10487): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
06-16 18:09:50.232: E/AndroidRuntime(10487): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
06-16 18:09:50.232: E/AndroidRuntime(10487): at dalvik.system.NativeStart.main(Native Method)

最后只好求助.Stackoverflow发问题时网页经常出问题，只好改加QQ群，最后得到android学习交流群的“成都-Young”提点，终于解决问题：

第50行的
```
convertView
```
```
//取得ListView的布局文件
50         convertView = mInflater.inflate(com.hanvon.moniter.R.layout.site_list_item, null);

放到56行的if语句里面进行初始化，这样convertView在为Null的时候就能正常初始化，而不是每次都提前初始化一个值，就直接运行71行的代码。

55         //View的绑定
```
```
56         if (convertView == null) {convertView = mInflater.inflate(com.hanvon.moniter.R.layout.site_list_item, null);
```
```
}
```
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原文地址：https://www.cnblogs.com/rockylearnstodevelop/p/NullPointerException.html