【Android笔记】listview加载性能优化及有多种listitem布局处理方式 – Fion_安

在android开发中Listview是一个很重要的组件,它以列表的形式根据数据的长自适应展示具体内容。

用户可以自由的定义listview每一列的布局,但当listview有大量的数据需要加载的时候,会占据大量内存,影响性能,这时候就需要按需填充并重新使用view来减少对象的创建。

 

ListView加载数据都是在

1 public View getView(int position, View convertView, ViewGroup parent) {
2
3   。。。。。。
4
5 }

方法中进行的(要自定义listview都需要重写listadapter:如 BaseAdapter,SimpleAdapter,CursorAdapter的等的getvView方法),

优化listview的加载速度就要让 convertView匹配列表类型,并最大程度上的重新使用convertView

 

其中,getview的加载方法一般有以下三种加载方式:

1、最慢的加载方式是每一次都重新定义一个View载入布局,再加载数据

1 public View getView(int position, View convertView, ViewGroup parent) {
2
3 View item = mInflater.inflate(R.layout.list_item_icon_text, null);
4
5 ((TextView) item.findViewById(R.id.text)).setText(DATA[position]);
6
7 ((ImageView) item.findViewById(R.id.icon)).setImageBitmap((position & 1) == 1 ? mIcon1 : mIcon2);
8
9 return item;
10
11 }

 

2、正确的加载方式是当convertView不为空的时候直接重新使用convertView从而减少了很多不必要的View的创建,然后加载数据

1 public View getView(int position, View convertView, ViewGroup parent) {
2
3 if (convertView == null) {
4
5 convertView = mInflater.inflate(R.layout.item, parent, false);
6
7 }
8
9 ((TextView) convertView.findViewById(R.id.text)).setText(DATA[position]);
10
11 ((ImageView) convertView.findViewById(R.id.icon)).setImageBitmap((position & 1) == 1 ? mIcon1 : mIcon2);
12
13 14
15 return convertView;
16
17 }

3、最快的方式是定义一个ViewHolder,将convetView的tag设置为ViewHolder,不为空时重新使用即可

1 static class ViewHolder {
2
3 TextView text;
4
5 ImageView icon;
6
7 }
8
9
10
11 public View getView(int position, View convertView, ViewGroup parent) {
12
13 ViewHolder holder;
14
15 if (convertView == null) {
16
17 convertView = mInflater.inflate(R.layout.list_item_icon_text,parent, false);
18
19 holder = new ViewHolder();
20
21 holder.text = (TextView) convertView.findViewById(R.id.text);
22
23 holder.icon = (ImageView) convertView.findViewById(R.id.icon);
24
25 convertView.setTag(holder);
26
27 } else {
28
29 holder = (ViewHolder) convertView.getTag();
30
31 }
32
33 holder.text.setText(DATA[position]);
34
35 holder.icon.setImageBitmap((position & 1) == 1 ? mIcon1 :mIcon2);
36
37 return convertView;
38
39 }

三种方式加载效率对比如下图所示:

说明:上述三个例子代码摘自google 2010 I/O大会

 

当处理一些耗时的资源加载的时候需要做到以下几点,以使你的加载更快更平滑:

1.   适配器在界面主线程中进行修改

2.   可以在任何地方获取数据但应该在另外一个地方请求数据

3.   在主界面的线程中提交适配器的变化并调用notifyDataSetChanged()方法

 

===============================分割线=========================================

 

那么如果存在多个item样式如何处理呢??

大致思路就是创建多个viewholder,在getViewType的时候设置不同位置的item用不同的viewholder

以下直接上代码:

1 class MyAdapter extends BaseAdapter{
2
3 Context mContext;
4 LinearLayout linearLayout = null;
5 LayoutInflater inflater;
6 TextView tex;
7 final int VIEW_TYPE = 3;
8 final int TYPE_1 = 0;
9 final int TYPE_2 = 1;
10 final int TYPE_3 = 2;
11
12 //各个布局的控件资源
13 class viewHolder1{
14 CheckBox checkBox;
15 TextView textView;
16 }
17 class viewHolder2{
18 TextView textView;
19 }
20 class viewHolder3{
21 ImageView imageView;
22 TextView textView;
23 }
24
25 public MyAdapter(Context context) {
26 // TODO Auto-generated constructor stub
27 mContext = context;
28 inflater = LayoutInflater.from(mContext);
29 }
30
31 @Override
32 public int getCount() {
33 // TODO Auto-generated method stub
34 return listString.size();
35 }
36
37 //每个convert view都会调用此方法,获得当前所需要的view样式
38 @Override
39 public int getItemViewType(int position) {
40 // TODO Auto-generated method stub
41 int p = position%6;
42 if(p == 0)
43 return TYPE_1;
44 else if(p < 3)
45 return TYPE_2;
46 else if(p < 6)
47 return TYPE_3;
48 else
49 return TYPE_1;
50 }
51
52 //返回样式的数量
53 @Override
54 public int getViewTypeCount() {
55 // TODO Auto-generated method stub
56 return 3;
57 }
58
59 @Override
60 public Object getItem(int arg0) {
61 // TODO Auto-generated method stub
62 return listString.get(arg0);
63 }
64
65 @Override
66 public long getItemId(int position) {
67 // TODO Auto-generated method stub
68 return position;
69 }
70
71 @Override
72 public View getView(int position, View convertView, ViewGroup parent) {
73 // TODO Auto-generated method stub
74 viewHolder1 holder1 = null;
75 viewHolder2 holder2 = null;
76 viewHolder3 holder3 = null;
77 int type = getItemViewType(position);
78
79
80 //无convertView,需要new出各个控件
81 if(convertView == null)
82 {
83 Log.e(“convertView = “, ” NULL”);
84
85 //按当前所需的样式,确定new的布局
86 switch(type)
87 {
88 case TYPE_1:
89 convertView = inflater.inflate(R.layout.listitem1, parent, false);
90 holder1 = new viewHolder1();
91 holder1.textView = (TextView)convertView.findViewById(R.id.textview1);
92 holder1.checkBox = (CheckBox)convertView.findViewById(R.id.checkbox);
93 Log.e(“convertView = “, “NULL TYPE_1”);
94 convertView.setTag(holder1);
95 break;
96 case TYPE_2:
97 convertView = inflater.inflate(R.layout.listitem2, parent, false);
98 holder2 = new viewHolder2();
99 holder2.textView = (TextView)convertView.findViewById(R.id.textview2);
100 Log.e(“convertView = “, “NULL TYPE_2”);
101 convertView.setTag(holder2);
102 break;
103 case TYPE_3:
104 convertView = inflater.inflate(R.layout.listitem3, parent, false);
105 holder3 = new viewHolder3();
106 holder3.textView = (TextView)convertView.findViewById(R.id.textview3);
107 holder3.imageView = (ImageView)convertView.findViewById(R.id.imageview);
108 Log.e(“convertView = “, “NULL TYPE_3”);
109 convertView.setTag(holder3);
110 break;
111 }
112 }
113 else
114 {
115 //有convertView,按样式,取得不用的布局
116 switch(type)
117 {
118 case TYPE_1:
119 holder1 = (viewHolder1) convertView.getTag();
120 Log.e(“convertView !!!!!!= “, “NULL TYPE_1”);
121 break;
122 case TYPE_2:
123 holder2 = (viewHolder2) convertView.getTag();
124 Log.e(“convertView !!!!!!= “, “NULL TYPE_2”);
125 break;
126 case TYPE_3:
127 holder3 = (viewHolder3) convertView.getTag();
128 Log.e(“convertView !!!!!!= “, “NULL TYPE_3”);
129 break;
130 }
131 }
132
133 //设置资源
134 switch(type)
135 {
136 case TYPE_1:
137 holder1.textView.setText(Integer.toString(position));
138 holder1.checkBox.setChecked(true);
139 break;
140 case TYPE_2:
141 holder2.textView.setText(Integer.toString(position));
142 break;
143 case TYPE_3:
144 holder3.textView.setText(Integer.toString(position));
145 holder3.imageView.setBackgroundResource(R.drawable.icon);
146 break;
147 }
148
149
150 return convertView;
151 }
152
153 }

参考原文:listview加载性能优化ViewHolder

参考原文:listView中多个listItem布局时,convertView缓存及使用

本文链接:【Android笔记】listview加载性能优化及有多种listitem布局处理方式,转载请注明。



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