Android开发中使用static变量应该注意的问题

package com.highxin.launcher01;



import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import android.app.Activity;
import android.content.ComponentName;
import android.content.ContentResolver;
import android.content.Context;
import android.content.Intent;
import android.content.pm.ApplicationInfo;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.content.pm.ResolveInfo;
import android.database.Cursor;
import android.graphics.drawable.Drawable;
import android.net.Uri;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.provider.ContactsContract;
import android.provider.ContactsContract.CommonDataKinds;
import android.provider.ContactsContract.PhoneLookup;
import android.provider.MediaStore;
import android.util.Log;
import android.view.KeyEvent;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.Window;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.TextView;

public class MainActivity extends Activity implements Runnable,OnItemClickListener{
    String name = "";
    String phoneNO = "";
    public static  List<Map<String, Object>>  contacts_list = new ArrayList<Map<String, Object>>();
    public static  List<Map<String, Object>>  gv_applist = new ArrayList<Map<String,Object>>();
    public static boolean switch_flag = false;
    public static boolean click_flag = false;
    public static boolean firstload_flag = false;//判断桌面是否是第一次加载
    public static List<Integer> click_position = new ArrayList<Integer>();
    private Intent serviceIntent;

    public static List<ResolveInfo> appInfos;
    public static List<ResolveInfo> showappInfos;
    public static  List<Map<String, Object>>  lv_applist = new ArrayList<Map<String,Object>>();
    public static  List<Map<String, Object>>  lv_addapplist = new ArrayList<Map<String,Object>>();
    public static  List<Map<String, Object>>  lv_delapplist = new ArrayList<Map<String,Object>>();
    
    static int []clickinfo;

    static GridView gv_app;
    
    String []appname ={"联系人","相机","电话","收音机","手电筒","更多"};
    int []appicon = {R.drawable.contact,R.drawable.camera,R.drawable.dial,R.drawable.fm,R.drawable.light_off,R.drawable.shop};
    
    private Handler mHandler = new Handler() {

        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            
             showappInfos = appInfos;
                
             
             for(int i=0; i<appInfos.size();i++) {
                 if((appInfos.get(i).loadLabel(getPackageManager()).equals("相机") &&
                     appInfos.get(i).activityInfo.packageName.equals("com.android.camera")) ||
                    (appInfos.get(i).loadLabel(getPackageManager()).equals("收音机") &&
                    appInfos.get(i).activityInfo.packageName.equals("com.miui.fmradio"))  ||
                    (appInfos.get(i).loadLabel(getPackageManager()).equals("老人桌面") &&
                     appInfos.get(i).activityInfo.packageName.equals("com.highxin.launcher01")) ){
                     showappInfos.remove(i);
                 }
             }
             clickinfo = new int[showappInfos.size()];
             gv_app.setAdapter(new GridViewAdapter(MainActivity.this,gv_applist));
        }     
    };

    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.activity_main);
        Drawable drawable_appicon = null;
        String s_appname = null;
        serviceIntent = new Intent(this, LightService.class);
//        if(!firstload_flag) {
            for(int i=0; i<appname.length;i++) {
                drawable_appicon = getResources().getDrawable(appicon[i]);
                s_appname = appname[i];
                Map<String, Object> map = new HashMap<String, Object>();
                map.put("appname", s_appname);
                map.put("drawable", drawable_appicon);
                
                gv_applist.add(map); 
             }
//            firstload_flag = true;
//        }   
        gv_app = (GridView) findViewById(R.id.gv_apps);
        
        gv_app.setOnItemClickListener(this);

        Thread t = new Thread(this);
        t.start();
    }
    
    
     private List<Map<String, Object>> fillMaps() {
         List<Map<String, Object>> items = new ArrayList<Map<String, Object>>();
         
         ContentResolver cr = getContentResolver();
         HashMap<String,ArrayList<String>> hashMap = new HashMap<String,ArrayList<String>>();
         Cursor phone = cr.query(CommonDataKinds.Phone.CONTENT_URI, 
           new String[] {
           CommonDataKinds.Phone.CONTACT_ID,
           CommonDataKinds.Phone.DISPLAY_NAME,      
           CommonDataKinds.Phone.NUMBER, 
           CommonDataKinds.Phone.DATA1
           //CommonDataKinds.StructuredPostal.DATA3,
           }, 
           null, null, null);
         while (phone.moveToNext()) {
          String contactId = phone.getString(phone.getColumnIndex(CommonDataKinds.Phone.CONTACT_ID));         
          String displayName = phone.getString(phone.getColumnIndex(CommonDataKinds.Phone.DISPLAY_NAME));
          String PhoneNumber = phone.getString(phone.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER));      
          String address = phone.getString(phone.getColumnIndex(CommonDataKinds.Phone.DATA1)); 
          
          //以contactId为主键，把同一人的所有电话都存到一起。
         ArrayList<String> ad = hashMap.get(contactId);
          if(ad == null){
           ad = new ArrayList<String>();
           ad.add(displayName);
           ad.add(PhoneNumber);
           //ad.add(address);
           
           hashMap.put(contactId, ad);
          }
          else{
           ad.add(PhoneNumber);
          }
          
         }
         phone.close();  
         
         ArrayList<String> tmpList;
         String tmpStr = "";
         int k;        
         Iterator iter = hashMap.entrySet().iterator();
         while (iter.hasNext()) {
          HashMap.Entry entry = (HashMap.Entry) iter.next();
             Object key = entry.getKey();
             Object val = entry.getValue();
             
             tmpList = (ArrayList) val;
             tmpStr =  tmpList.get(1);
             //注释掉的为读取多个联系人的方法
//             for(k = 1; k < tmpList.size(); k++){
//              tmpStr = tmpStr + tmpList.get(k) + ',' ;
//             }
             
             HashMap<String, Object> tmpMap = new HashMap<String, Object>();        
             tmpMap.put("name", tmpList.get(0));
             tmpMap.put("phoneNO", tmpStr);
             tmpMap.put("img", R.drawable.image);
             
             items.add(tmpMap);            
         }                   
         return items;        
     }


    class GridViewAdapter extends BaseAdapter{

        LayoutInflater inflater;
        List<Map<String, Object>> gvlist;
        public GridViewAdapter(Context context,List<Map<String, Object>> locallist) {
            inflater = LayoutInflater.from(context);
            gvlist = locallist;
        }
        @Override
        public int getCount() {
            // TODO Auto-generated method stub
            return gvlist.size();
        }

        @Override
        public Object getItem(int position) {
            // TODO Auto-generated method stub
            return gvlist.get(position);
        }

        @Override
        public long getItemId(int position) {
            // TODO Auto-generated method stub
            return position;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            // TODO Auto-generated method stub
        
                View view = inflater.inflate(R.layout.gv_item, null);
                TextView name = (TextView)view.findViewById(R.id.gv_item_appname);
                ImageView iv = (ImageView)view.findViewById(R.id.gv_item_icon);
                name.setText((CharSequence) gvlist.get(position).get("appname"));
                iv.setImageDrawable((Drawable) gvlist.get(position).get("drawable"));
                
            return view;
        }
        
    }
    

    @Override
    protected void onResume() {
        super.onResume();
         gv_app.setAdapter(new GridViewAdapter(MainActivity.this,gv_applist));
    }

    @Override
    public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
        // TODO Auto-generated method stub
        switch(arg2) {
        
            case 0:{
                    contacts_list = fillMaps();
                    Intent contact  = new Intent(MainActivity.this, Contacts.class);
                    startActivity(contact);
                    }break;
            case 1:{
               Intent imageCaptureIntent = new Intent("android.media.action.STILL_IMAGE_CAMERA"); 
               startActivityForResult(imageCaptureIntent,1);
            }break;
            case 2:{
                Intent i = new Intent();
                String packageName = "com.android.contacts";
                String mainActivityName = "com.android.contacts.activities.TwelveKeyDialer";
                i.setComponent(new ComponentName(packageName,mainActivityName));
                startActivity(i);
            }break;
            case 3:{
                Intent intent = new Intent();
                intent.setPackage("com.miui.fmradio");        
                startActivityForResult(intent, 3);
                }break;
            case 4:{
                    switch_flag = !switch_flag;
                    if(switch_flag) {
                        startService(serviceIntent);
                         ImageView iv = (ImageView) arg1.findViewById(R.id.gv_item_icon);
                         iv.setImageResource(R.drawable.light);
                        
                    }else {
                        stopService(serviceIntent);
                         ImageView iv = (ImageView) arg1.findViewById(R.id.gv_item_icon);
                         iv.setImageResource(R.drawable.light_off);
                    }
                }break;
            case 5:{
                Intent applist  = new Intent(MainActivity.this, AppList.class);
                startActivityForResult(applist,5);
                }break;
            default:{
                Intent i = new Intent();
                String packageName = (String) MainActivity.gv_applist.get(arg2).get("pkgname");
                String mainActivityName = (String) MainActivity.gv_applist.get(arg2).get("activityname");
                i.setComponent(new ComponentName(packageName,mainActivityName));
                startActivity(i);
                
                
            }break;
        }
    }

    @Override
    public void run() {

         appInfos = getResolveInfoLists();
         mHandler.sendEmptyMessage(0);
    }
    
    
    /**
     * @Title: getResolveInfoLists
     * @Description: 它是通过解析< Intent-filter>标签得到有 　　< action
     *               android:name=”android.intent.action.MAIN”/> 　　< action
     *               android:name=”android.intent.category.LAUNCHER”/>
     * @param ：
     * @return List<ResolveInfo>
     * @throws
     */
    private List<ResolveInfo> getResolveInfoLists() {

        // TODO Auto-generated method stub
        PackageManager packageManager = this.getPackageManager();

        Intent intent = new Intent(Intent.ACTION_MAIN);
        intent.addCategory(Intent.CATEGORY_LAUNCHER);

        return packageManager.queryIntentActivities(intent, 0);
    }

    @Override
    protected void onDestroy() {
        // TODO Auto-generated method stub
        super.onDestroy();
//        gv_applist.clear();
    }

//    @Override
//    public boolean onKeyDown(int keyCode, KeyEvent event) {
//        if (keyCode == KeyEvent.KEYCODE_BACK){
//            return true;
//        }
//        if(keyCode == KeyEvent.KEYCODE_HOME) {
//            gv_applist.clear();
//        }
//    
//    return super.onKeyDown(keyCode, event);
//
//    }
}

每次按返回键，重新进入程序gv_applist.add(map)，会在原来的基础上不断增加。

找到一篇文章是描述的大概也是这个问题：

突然想到了一个问题，因为我在这两个Activity中使用了不一样的结束方式，一个为System.exit(0);一种为finishi();感觉可能是这两个方式造成的，后来经过测试，确实是这两个方式造成的，如果是使用System.exit（0）；的方式的话，等于把这个Acitvity结束了，因此他所操作过的数据都不会再存在了，系统也许认为没有存在的必要了吧，使用finishi();的话，虽然也是退出，但是这个并不是释放资源，只是把当前的Activity推向后台，不再显示，但是他不释放资源，具体资源什么时候释放，由系统决定，当然System.exit（0）；这种形式，也并不是真正的退出系统，因为我们还可能有别的Activity在运行，但是他确实把资源释放了！这个是为什么，不太明白！

的确重写onDestroy(),调用finish方法还是有这个问题，但是调用System.exit(0)就不存在这个问题啦。如果仅仅就是解决这个问题，当然可以继续坚持使用static变量，要么在destroy方法中对gv_applist清零,要么设置变量判断是不是第一次启动。

 @Override
 protected void onDestroy() {
  // TODO Auto-generated method stub
  super.onDestroy();
//  System.exit(0);
  finish();
  
//  gv_applist.clear();
 }

但当把这个程序变成桌面程序时,又有一个问题出现啦

         <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
                 <category android:name="android.intent.category.HOME" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>        

 

MainActivity中还有一个变量：static int []clickinfo;这个变量只在点击应用程序后面的按钮时值才会发生改变，为+号时，点击会将图标添加到主屏幕，添加完成之后立即变成-号

gv_applist决定主屏幕上加载哪些图标，但当添加完一个图标之后，立即按home键，（桌面程序被推入后台，但是不释放资源，重启桌面程序）会发现主屏幕仍然存在这个图标，但是原来应用列表里面的-号却变成了加号。

if (MainActivity.clickinfo[position] == 0) {
                ibt_operate.setImageDrawable(getResources().getDrawable(
                        R.drawable.add));
            } else {
                ibt_operate.setImageDrawable(getResources().getDrawable(
                        R.drawable.del));
            }

但应用列表里的图标仅仅依据clickinfo变量加载，所以可以断定clickinfo被初始化成全零啦。

static int []clickinfo;
public static  List<Map<String, Object>>  lv_applist = new ArrayList<Map<String,Object>>();

原来定义时，clickinfo没有使用new方法，这种变量进入后台后值是不能够保存的。

如果使用全局变量：

1、尽量减少对代码的同步计算

例如：

for(int i =0;i<list.size;i++){
 }

应替换为：

for(int i = 0, int len= list.size();i<len;i++){
   }

2、尽量采用lazy loading的策略，在需要的时候才开始创建

例如：

String str = "aaa";
    if(i==1){
     list.add(str)
    }

应替换为：

 if(i ==1){
     String str = "aaa"
      list.add(str)
    }