Android_ListView适配器
ListView如何优化
- 复用convertView缓存(减少ListView绘制).
- 自定义静态类ViewHolder(减少findViewById次数)，通过setTag()、getTag()获取holder实例.
- 使用分页加载.
- 使用软引用WeakReference引用ImageView对象：当item划出屏幕，可以释放对大图片的引用，节省内存，提高效率.
- 另外对图片还可以使用LruCache和三级缓存来优化.
正常使用方式
public class MyAdapter extends BaseAdapter {
private LayoutInflater mInflater;
private Context ctx;
private List<String> mDatas;
public MyAdapter(Context ctx, List<String> mDatas) {
mInflater = LayoutInflater.from(ctx);
this.ctx = ctx;
this.mDatas = mDatas;
}
@Override
public int getCount() {
return mDatas.size(); // 固定
}
@Override
public Object getItem(int position) {
return mDatas.get(position); // 固定
}
@Override
public long getItemId(int position) {
return position; // 固定
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder = null;
if (convertView == null) { // 复用convertView缓存
convertView = mInflater.inflate(R.layout.item_str, null); // 条目布局
holder = new ViewHolder();
holder.tv = (TextView) convertView.findViewById(R.id.tv); // holder存储控件
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
holder.tv.setText(mDatas.get(position));
return convertView;
}
private final class ViewHolder {
TextView tv;
}
}
上述代码大家都很熟悉，基本遇到就是一套，都写烂了，分析一下
- 复写的三个方法都是固定的，很好抽取.
- getView中通过set、get处理ViewHolder对象可以抽取.
- holder中的findViewById可以抽取.
提炼
PART_A：Adapter
package com.catface.cadapter;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import java.util.List;
/** * @desc 使用泛型，接收不同类型的对象 */
public abstract class CAdapter<T> extends BaseAdapter {
protected Context ctx;
protected List<T> datas;
protected LayoutInflater inflater;
private int layoutId;
// arg1-3：上下文 | 集合<泛型bean> | 条目布局
public CAdapter(Context ctx, List<T> datas, int layoutId) {
this.ctx = ctx;
this.datas = datas;
this.inflater = LayoutInflater.from(ctx);
this.layoutId = layoutId;
}
@Override public int getCount() {
return datas == null ? 0 : datas.size();
}
@Override public T getItem(int position) {
return datas == null ? null : datas.get(position);
}
@Override public long getItemId(int position) {
return position;
}
/** * @desc 1.获取ViewHolder对象(上下文、复用缓存、父布局、条目布局) */
@Override public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder = ViewHolder.get(ctx, convertView, parent, layoutId, position);
convert(holder, getItem(position)); // ------>> 暴露抽象方法
return holder.getConvertView(); // 设置结束各个组件，返回ViewHolder对象方便继续设置控件值
}
/** * @desc 暴露出去并传入holder与bean：拿着控件设置值 */
public abstract void convert(ViewHolder holder, T t);
}
PART_B：ViewHolder
package com.catface.cadapter;
import android.annotation.SuppressLint;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Paint;
import android.graphics.Typeface;
import android.graphics.drawable.Drawable;
import android.os.Build;
import android.text.util.Linkify;
import android.util.SparseArray;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.animation.AlphaAnimation;
import android.widget.Checkable;
import android.widget.ImageView;
import android.widget.ProgressBar;
import android.widget.RatingBar;
import android.widget.TextView;
/** * @desc 待修复问题： * * 1.CheckBox选中错位(复用convertView所致) √ * a.在Bean中添加isChecked字段 * b.在ListView中用ArrayList数组记录holder中当前选中的CheckBox * * 2.图片显示错位 × * * 3.上拉刷新 + 下拉加载 × */
public class ViewHolder {
private Context ctx; // 上下文
private View convertView; // 复用缓存
private int mLayoutId; // 条目布局
private SparseArray<View> views; // 各组件及对应id(SparseArray代替HashMap，提高效率)
private int position;
public ViewHolder(Context ctx, ViewGroup parent, int layoutId, int position) {
this.ctx = ctx;
this.convertView = LayoutInflater.from(ctx).inflate(layoutId, parent, false);
this.mLayoutId = layoutId;
this.views = new SparseArray<View>();
this.position = position;
this.convertView.setTag(this);
}
/** * @desc 通过setTag()和getTag()来获取ViewHolder对象 */
public static ViewHolder get(Context ctx, View convertView, ViewGroup parent, int layoutId, int position) {
if (convertView == null) {
return new ViewHolder(ctx, parent, layoutId, position);
} else {
ViewHolder holder = (ViewHolder) convertView.getTag();
holder.position = position;
return holder;
}
}
/** * @desc 获取当前holder的position */
public int getPosition() {
return position;
}
public int getLayoutId() {
return mLayoutId;
}
/** * @desc 通过viewId获取控件 */
@SuppressWarnings("unchecked")
public <T extends View> T getViewByViewId(int viewId) {
View view = views.get(viewId);
if (view == null) {
view = convertView.findViewById(viewId);
views.put(viewId, view);
}
return (T) view;
}
public View getConvertView() {
return convertView;
}
/************************************************ PS：图片可以使用第三方工具类加载图片 ************************************************/
/** 设置TextView文本 */
public ViewHolder setText(int viewId, String text) {
((TextView) getViewByViewId(viewId)).setText(text);
return this;
}
/** 设置TextView颜色 */
public ViewHolder setTextColor(int viewId, int textColor) {
((TextView) getViewByViewId(viewId)).setTextColor(textColor);
return this;
}
/** 设置TextView颜色 */
public ViewHolder setTextColorRes(int viewId, int textColorRes) {
((TextView) getViewByViewId(viewId)).setTextColor(ctx.getResources().getColor(textColorRes));
return this;
}
/** 设置文本字体 */
public ViewHolder setTypeface(Typeface typeface, int... viewIds) {
for (int viewId : viewIds) {
TextView view = getViewByViewId(viewId);
view.setTypeface(typeface);
view.setPaintFlags(view.getPaintFlags() | Paint.SUBPIXEL_TEXT_FLAG);
}
return this;
}
/** 设置图片：资源id */
public ViewHolder setImageResource(int viewId, int resId) {
((ImageView) getViewByViewId(viewId)).setImageResource(resId);
return this;
}
/** 设置图片：Bitmap */
public ViewHolder setImageBitmap(int viewId, Bitmap bitmap) {
((ImageView) getViewByViewId(viewId)).setImageBitmap(bitmap);
return this;
}
/** 设置图片：Drawable */
public ViewHolder setImageDrawable(int viewId, Drawable drawable) {
((ImageView) getViewByViewId(viewId)).setImageDrawable(drawable);
return this;
}
/** 设置背景色 */
public ViewHolder setBackgroundColor(int viewId, int color) {
getViewByViewId(viewId).setBackgroundColor(color);
return this;
}
/** 设置背景色 */
public ViewHolder setBackgroundRes(int viewId,