[listview] listview优化 - Android 4.0 Documentation

1、复用convertView
2、缓存findViewById(),static viewHolder
3、软引用、弱引用
用LruCache替换
4、图片缩放

1、复用convertView

2、ViewHolder缓存查找到的组件的引用，防止多次查找，浪费内存和耗时

private static class ViewHolder {

private TextView tv;

private ImageView iv;

}
......

View view = null;

ViewHolder viewHolder = null;

if (convertView != null && convertView instanceof LinearLayout) {

System.out.println("复用以前的convertView:" + position);

view = convertView;

viewHolder = (ViewHolder) view.getTag();

}else {

System.out.println("新创建View:" + position);

view = View.inflate(getApplicationContext(), R.layout.bitmap_list, null);

viewHolder = new ViewHolder();

viewHolder.tv = (TextView) view.findViewById(R.id.tv);

viewHolder.iv = (ImageView) view.findViewById(R.id.iv);

view.setTag(viewHolder);

}

3、软引用和弱引用

// TODO 1:软引用、虚引用

// SoftReference<ImageView> softReferenceBitmap = new SoftReference<ImageView>(iv);

WeakReference<Bitmap> softReferenceBitmap = new WeakReference<Bitmap>(bitmap);

bitmap.recycle();

bitmap = null;
......

WeakReference<Bitmap> softReferenceBitmap = softReferenceImages.get(position);

Bitmap refBitmap = softReferenceBitmap.get();

if (refBitmap == null) {

// System.gc();

System.out.println("被GC回收：" + position);

refBitmap = scaleBitmap(imagesIds[position]);

}

4、图片缩放

/**

* //TODO 2：图片缩放

* @param resId 要缩放的图片的id

* @return 缩放后的图片的bitmap

*/

@SuppressLint("NewApi")

// api13

private Bitmap scaleBitmap(int resId) {

Options opts = new Options();

opts.inJustDecodeBounds = true;// 不是真正的去解析图片，而是解析图片的头

BitmapFactory.decodeResource(getResources(), resId, opts);

int outWidth = opts.outWidth;

int outHeight = opts.outHeight;

System.out.println("图片宽度：" + outWidth);

System.out.println("图片高度：" + outHeight);

// 获取屏幕尺寸

Display display = wm.getDefaultDisplay();

Point screenSize = new Point();

display.getSize(screenSize);

int window_width = screenSize.x;

int window_height = screenSize.y;

System.out.println("屏幕宽度：" + window_width);

System.out.println("屏幕高度：" + window_height);

int scale = 1;

int scaleX = outWidth / window_width;

int scaleY = outHeight / window_height;

if (scaleX < scaleY) {// 按照最大的缩放

scale = scaleY;

} else if (scaleX >= scaleY) {

scale = scaleX;

}

opts.inSampleSize = scale;// 缩放比例,如果大于0，缩放比例为x和y轴各缩放1/scale,小于0，原图

System.out.println("缩放比例：" + scale);

opts.inJustDecodeBounds = false;// 重新设置为解析全图

return BitmapFactory.decodeResource(getResources(), resId, opts);

}

全部核心代码：

package cn.zengfansheng.softreferencetest;

import java.lang.ref.WeakReference;

import java.util.ArrayList;

import android.annotation.SuppressLint;

import android.app.Activity;

import android.content.Context;

import android.graphics.Bitmap;

import android.graphics.BitmapFactory;

import android.graphics.BitmapFactory.Options;

import android.graphics.Point;

import android.os.Bundle;

import android.view.Display;

import android.view.View;

import android.view.ViewGroup;

import android.view.WindowManager;

import android.widget.BaseAdapter;

import android.widget.ImageView;

import android.widget.LinearLayout;

import android.widget.ListView;

import android.widget.TextView;

public class MainActivity extends Activity {

private ListView lv;

private int[] imagesIds;

// private ArrayList<SoftReference<ImageView>> softReferenceImages;

private ArrayList<WeakReference<Bitmap>> softReferenceImages;

private WindowManager wm;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

wm = (WindowManager) this.getSystemService(Context.WINDOW_SERVICE);

initData();

lv = (ListView) this.findViewById(R.id.lv);

MyAdapter adapter = new MyAdapter();

lv.setAdapter(adapter);

// VMRuntime

}

@SuppressLint("NewApi")

public void initData() {

imagesIds = LoadRes.loadResId();

// softReferenceImages = new ArrayList<SoftReference<ImageView>>();

softReferenceImages = new ArrayList<WeakReference<Bitmap>>();

for (int i : imagesIds) {

Bitmap bitmap = scaleBitmap(i);

// TODO 1:软引用、虚引用

// SoftReference<ImageView> softReferenceBitmap = new SoftReference<ImageView>(iv);

WeakReference<Bitmap> softReferenceBitmap = new WeakReference<Bitmap>(bitmap);

bitmap.recycle();

bitmap = null;

System.gc();

softReferenceImages.add(softReferenceBitmap);

}

/**

* //TODO 2：图片缩放

* @param resId 要缩放的图片的id

* @return 缩放后的图片的bitmap

*/

@SuppressLint("NewApi")

// api13

private Bitmap scaleBitmap(int resId) {

Options opts = new Options();

opts.inJustDecodeBounds = true;// 不是真正的去解析图片，而是解析图片的头

BitmapFactory.decodeResource(getResources(), resId, opts);

int outWidth = opts.outWidth;

int outHeight = opts.outHeight;

System.out.println("图片宽度：" + outWidth);

System.out.println("图片高度：" + outHeight);

// 获取屏幕尺寸

Display display = wm.getDefaultDisplay();

Point screenSize = new Point();

display.getSize(screenSize);

int window_width = screenSize.x;

int window_height = screenSize.y;

System.out.println("屏幕宽度：" + window_width);

System.out.println("屏幕高度：" + window_height);

int scale = 1;

int scaleX = outWidth / window_width;

int scaleY = outHeight / window_height;

if (scaleX < scaleY) {// 按照最大的缩放

scale = scaleY;

} else if (scaleX >= scaleY) {

scale = scaleX;

}

opts.inSampleSize = scale;// 缩放比例,如果大于0，缩放比例为x和y轴各缩放1/scale,小于0，原图

System.out.println("缩放比例：" + scale);

opts.inJustDecodeBounds = false;// 重新设置为解析全图

return BitmapFactory.decodeResource(getResources(), resId, opts);

}

// TODO 3: ViewHolder,findViewByid() 查找id的优化

private static class ViewHolder {

private TextView tv;

private ImageView iv;

}

// TODO ：适配器

private class MyAdapter extends BaseAdapter {

@Override

public int getCount() {

return softReferenceImages.size();

}

@Override

public Object getItem(int position) {

return null;

}

@Override

public long getItemId(int position) {

return 0;

}

@Override

public View getView(int position, View convertView, ViewGroup parent) {

// TODO 4：使用convertView缓存

View view = null;

ViewHolder viewHolder = null;

if (convertView != null && convertView instanceof LinearLayout) {

System.out.println("复用以前的convertView:" + position);

view = convertView;

viewHolder = (ViewHolder) view.getTag();

}else {

System.out.println("新创建View:" + position);

view = View.inflate(getApplicationContext(), R.layout.bitmap_list, null);

viewHolder = new ViewHolder();

viewHolder.tv = (TextView) view.findViewById(R.id.tv);

viewHolder.iv = (ImageView) view.findViewById(R.id.iv);

view.setTag(viewHolder);

}

//SoftReference<ImageView> softReferenceBitmap = softReferenceImages.get(position);

WeakReference<Bitmap> softReferenceBitmap = softReferenceImages.get(position);

Bitmap refBitmap = softReferenceBitmap.get();

if (refBitmap == null) {

// System.gc();

System.out.println("被GC回收：" + position);

refBitmap = scaleBitmap(imagesIds[position]);

}

viewHolder.tv.setText("图片名称：1000" + Math.random() * 100);

viewHolder.iv.setImageBitmap(refBitmap);

return view;

}