ListView的優化

ListView的優化：

（前兩點都是利用ListView的自身優化機制優化【緩存優化】）

1.利用ListView自身的緩存機制，他會緩存條目中的一個條目item，當listview第一屏顯示完成之后，就會出現一個緩存條目，其實就是BaseAdapter里面的public View getView(int position, View convertView, ViewGroup parent)。

2.減少findViewById()的次數，findViewById是一個相對比較耗性能的操作，因為這個操作每次都需要到布局中去查找文件。把item里面的控件封裝成一個javaBean，當item條目被加載的時候就去找到對應的控件。

3.利用時間去換取時間，比如開機優化，把一些重要的程序先啟動了，啟動完系統之后再啟動其他程序。

4.利用空間去換取時間，把要獲取的數據先加載到內存里面，再處理數據的時候，直接從內存中獲取。

   例如：減少數據庫的頻繁打開和關閉和減少查詢的次數。

 

Demo：需求： 程序鎖，將手機中所有的應用顯示出來，是否是帶鎖的應用用數據庫進行存儲，通過ListView顯示。

import java.util.List;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.animation.TranslateAnimation;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.RelativeLayout;
import android.widget.TextView;

import com.android.hzy.mobilesafe.R;
import com.android.hzy.mobilesafe.dao.AppLockDao;
import com.android.hzy.mobilesafe.domain.AppInfo;
import com.android.hzy.mobilesafe.engine.AppInfoService;

public class AppLockManagerActivity extends Activity {

    protected static final int SUCCESS_GET_APPLICATION = 0;
    private ListView lv_applockmanager;
    private RelativeLayout rl_loading;
    private AppInfoService appInfoService;
    private List<AppInfo> appInfos;
    
    private List<String> appLocks; // 程序鎖應用集合
    
    private AppLockManagerAdapter mAdapter;
    private AppLockDao appLockDao;
    private Handler mHandler = new Handler(){

        public void handleMessage(Message msg) {
            switch (msg.what) {
            case SUCCESS_GET_APPLICATION:
                appLocks = appLockDao.findAll();
                mAdapter = new AppLockManagerAdapter();
                lv_applockmanager.setAdapter(mAdapter);
                rl_loading.setVisibility(View.GONE);
                break;

            default:
                break;
            }
        }
        
    };
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.app_lock_manager);
        
        lv_applockmanager = (ListView) findViewById(R.id.lv_applockmanager);
        rl_loading = (RelativeLayout) findViewById(R.id.rl_loading);
        appInfoService = new AppInfoService(this);
        
        new Thread() {
            public void run() {
                appInfos = appInfoService.getAppInfos();
                Message msg = new Message();
                msg.what = SUCCESS_GET_APPLICATION;
                mHandler.sendMessage(msg);
            };
        }.start();
        
        appLockDao = new AppLockDao(this);
        
        lv_applockmanager.setOnItemClickListener(new MyOnItemClickListener());
    }
    
    /**********listview條目點擊事件*************************/
    private final class MyOnItemClickListener implements OnItemClickListener{

        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position,
                long id) {
            // TODO Auto-generated method stub
            // 通過ViewHolder的iv_lock 減少findViewById
            ImageView iv_lock = ((ViewHolder)view.getTag()).iv_lock;
            AppInfo appInfo = (AppInfo) mAdapter.getItem(position);
//            boolean isLockApp = appLockDao.isLockApp(appInfo.getPackagename()); 減少數據庫的查詢
            boolean isLockApp = appLocks.contains(appInfo.getPackagename());
            if (isLockApp) {
                // 如果有鎖  就解鎖
                appLockDao.delete(appInfo.getPackagename());
                // 解鎖需要將集合中帶鎖應用的移除
                appLocks.remove(appInfo.getPackagename());
                iv_lock.setImageResource(R.drawable.unlock);
            } else {
                // 如果沒有鎖  就加鎖
                appLockDao.add(appInfo.getPackagename());
                // 加鎖需要將有鎖的集合中添加該應用
                appLocks.add(appInfo.getPackagename());
                iv_lock.setImageResource(R.drawable.lock);
            }
            
            // 設置動畫
            TranslateAnimation animation = new TranslateAnimation(0, 80, 0, 0);
            animation.setDuration(300);
            view.startAnimation(animation);
        }
        
    }
    
    /**
     * 適配器
     */
    public final class AppLockManagerAdapter extends BaseAdapter{
        
        private LayoutInflater mInflater;
        
        public AppLockManagerAdapter() {
            // TODO Auto-generated constructor stub
            mInflater = getLayoutInflater();
        }
        
        @Override
        public int getCount() {
            // TODO Auto-generated method stub
            return appInfos.size();
        }

        @Override
        public Object getItem(int position) {
            // TODO Auto-generated method stub
            return appInfos.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 = null;
            ViewHolder holder = null;
            if (convertView != null) {
                view = convertView;
                holder = (ViewHolder) view.getTag();
                Log.i("i", " convertView != null  緩存不等於空  使用緩存");
                
            } else {
                Log.i("i", " convertView == null  緩存等於空");
                view = mInflater.inflate(R.layout.app_lock_manager_item, null);
                holder = new ViewHolder();
                holder.iv_appicon = (ImageView) view.findViewById(R.id.iv_appicon);
                holder.tv_appname = (TextView) view.findViewById(R.id.tv_appname);
                holder.iv_lock = (ImageView) view.findViewById(R.id.iv_lock);
                view.setTag(holder);
            }
            AppInfo appInfo = appInfos.get(position);
            
            ImageView iv_appicon = holder.iv_appicon;
            TextView tv_appname = holder.tv_appname;
            ImageView iv_lock = holder.iv_lock;
            
            iv_appicon.setImageDrawable(appInfo.getApp_icon());
            tv_appname.setText(appInfo.getApp_name());
            
//            boolean isLockApp = appLockDao.isLockApp(appInfo.getPackagename());
            boolean isLockApp = appLocks.contains(appInfo.getPackagename()); // 此功能優化后  不用每次查詢數據庫 直接將所有有鎖的程序都放入集合中存儲
            if(isLockApp){
                iv_lock.setImageResource(R.drawable.lock);
            }else{
                iv_lock.setImageResource(R.drawable.unlock);
            }
            
            return view;
        }
        
    }
    
    static class ViewHolder{
        ImageView iv_appicon;
        TextView tv_appname;
        ImageView iv_lock;
    }
}

 

效果如上圖，當第一次加載ListView里面條目時，我們所能看見的都是沒有緩存的，當我們往下滑動后，控件都是使用緩存中的控件，減少了findViewById的次數