一、概述
該擴充卡主要還是對adapter和viewholder進行了抽象和封裝,使之能夠在任何item下都可以運用。
二、ViewHolder類
package com.tianzhao.myutils.adapter;
import android.content.Context;
import android.graphics.Bitmap;
import android.util.SparseArray;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
public class ViewHolder {
private final SparseArray<View> mViews;
private int mPosition;
private View mConvertView;
private ViewHolder(Context context, ViewGroup parent, int layoutId,
int position) {
this.mPosition = position;
this.mViews = new SparseArray<View>();
mConvertView = LayoutInflater.from(context).inflate(layoutId, parent,
false);
// setTag
mConvertView.setTag(this);
}
/**
* 拿到一個ViewHolder對象
*
* @param context
* @param convertView
* @param parent
* @param layoutId
* @param position
* @return
*/
public static ViewHolder get(Context context, View convertView,
ViewGroup parent, int layoutId, int position) {
if (convertView == null) {
return new ViewHolder(context, parent, layoutId, position);
}
else {
ViewHolder holder = (ViewHolder) convertView.getTag();
holder.mPosition = position;
return holder;
}
}
public View getConvertView() {
return mConvertView;
}
/**
* 通過控件的Id擷取對于的控件,如果沒有則加入views
*
* @param viewId
* @return
*/
@SuppressWarnings("unchecked")
public <T extends View> T getView(int viewId) {
View view = mViews.get(viewId);
if (view == null) {
view = mConvertView.findViewById(viewId);
mViews.put(viewId, view);
}
return (T) view;
}
/**
* 為TextView設定字元串
*
* @param viewId
* @param text
* @return
*/
public ViewHolder setText(int viewId, String text) {
TextView view = getView(viewId);
view.setText(text);
return this;
}
/**
* 為ImageView設定圖檔
*
* @param viewId
* @param drawableId
* @return
*/
public ViewHolder setImageResource(int viewId, int drawableId) {
ImageView view = getView(viewId);
view.setImageResource(drawableId);
return this;
}
/**
* 為ImageView設定圖檔
*
* @param viewId
* @param drawableId
* @return
*/
public ViewHolder setImageBitmap(int viewId, Bitmap bm) {
ImageView view = getView(viewId);
view.setImageBitmap(bm);
return this;
}
public int getPosition() {
return mPosition;
}
}
三、通用Adapter的CommonAdapter類
package com.tianzhao.myutils.adapter;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import java.util.List;
public abstract class CommonAdapter<T> extends BaseAdapter {
protected LayoutInflater mInflater;
protected Context mContext;
protected List<T> mDatas;
protected final int mItemLayoutId;
public CommonAdapter(Context context, List<T> mDatas, int itemLayoutId) {
this.mContext = context;
this.mInflater = LayoutInflater.from(mContext);
this.mDatas = mDatas;
this.mItemLayoutId = itemLayoutId;
}
@Override
public int getCount() {
return mDatas == null ? 0 : mDatas.size();
}
@Override
public T getItem(int position) {
return mDatas.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
final ViewHolder viewHolder = getViewHolder(position, convertView,
parent);
convert(viewHolder, getItem(position));
return viewHolder.getConvertView();
}
public abstract void convert(ViewHolder helper, T item);
public void setDatas(List<T> mDatas) {
this.mDatas = mDatas;
notifyDataSetChanged();
}
private ViewHolder getViewHolder(int position, View convertView,
ViewGroup parent) {
return ViewHolder.get(mContext, convertView, parent, mItemLayoutId,
position);
}
}
四、MainActivity中的使用
package com.tianzhao.myutils;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.ListView;
import android.widget.Toast;
import com.tianzhao.myutils.adapter.CommonAdapter;
import com.tianzhao.myutils.adapter.ViewHolder;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity {
private List<UserBean> mDatas;
private ListView lv;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
lv = (ListView) findViewById(R.id.lv);
initDatas();
lv.setAdapter(new CommonAdapter<UserBean>(MainActivity.this, mDatas, R.layout.item) {
@Override
public void convert(final ViewHolder holder, UserBean u) {
CheckBox cb = holder.getView(R.id.cb);
if (u.isChecked()) {
cb.setChecked(true);
} else {
cb.setChecked(false);
}
holder.setText(R.id.name, u.getName());
holder.setText(R.id.name, u.getNumb());
cb.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
mDatas.get(holder.getPosition()).setIsChecked(isChecked);
}
});
}
});
lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
Toast.makeText(MainActivity.this,"點選了第 "+position+" 個Item",Toast.LENGTH_SHORT).show();
}
});
}
private void initDatas() {
mDatas = new ArrayList<>();
for (int i = 0; i < 60; i++) {
UserBean user = new UserBean("姓名 : " + i + "", "号碼 :" + i + "" + i + "" + i + "" + i + "" + i + "");
mDatas.add(user);
}
}
}
下面貼上一個效果圖
![](https://img.laitimes.com/img/_0nNw4CM6IyYiwiM6ICdiwiIyVGduV2QvwVe0lmdhJ3ZvwFM38CXlZHbvN3cpR2Lc1TPB10QGtWUCpEMJ9CXsxWam9CXwADNvwVZ6l2c052bm9CXUJDT1wkNhVzLcRnbvZ2LcZXUYpVd1kmYr50MZV3YyI2cKJDT29GRjBjUIF2LcRHelR3LcJzLctmch1mclRXY39DM5YTOyUTNxETMyITM1EDMy8CX0Vmbu4GZzNmLn9Gbi1yZtl2Lc9CX6MHc0RHaiojIsJye.jpg)
在這裡貼上Demo下載下傳位址
說道這那就再說一下ListView的優化把,在ListView中,主要就是優化View的重繪。這樣可以減少記憶體消耗,同時加快Item的加載速度。總體上來說就是以下三點:
1、在getView方法中要考慮方法傳進來的參數contentView是否為null,如果為null就建立contentView并傳回,如果不為null則直接使用。在這個方法中盡可能少建立view。
2、給contentView設定tag(setTag()),傳入一個viewHolder對象,用于緩存要顯示的資料,可以達到圖像資料異步加載的效果。
3、如果listview需要顯示的item很多,就要考慮分頁加載。比如一共要顯示100條或者更多的時候,我們可以考慮先加載20條,等使用者拉到清單底部的時候再去加載接下來的20條。