ListView、処理の高速化

findViewByIdを一度だけ実行する。

setTagを使用する。

********************　　MainActivity.java　　********************

package jp.lesson.studyandroid;

import java.util.ArrayList;

import android.os.Bundle;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.ListAdapter;
import android.widget.TextView;
import android.app.ListActivity;
import android.content.Context;

public class MainActivity extends ListActivity {

    @Override

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
       
        ValueItem data1 = new ValueItem();
        data1.setMsg("Sample data0");
        ValueItem data2 = new ValueItem();
        data2.setMsg("Sample data1");
        ValueItem data3 = new ValueItem();
        data3.setMsg("Sample data2");
       
        ArrayList<ValueItem> list = new ArrayList<ValueItem>();
        list.add(data1);
        list.add(data2);
        list.add(data3);
       
        ListAdapter adapter = new ValueItemAdapter(getApplicationContext(),list);
       
        setListAdapter(adapter);
    }
   
    public class ValueItemAdapter extends ArrayAdapter<ValueItem> {
        Context context;
        LayoutInflater inflater;

        public ValueItemAdapter(Context context, ArrayList<ValueItem> objects) {

            super(context, 0, objects);
            this.context = context;
            this.inflater = LayoutInflater.from(context);
        }

        @Override

        public View getView(int position, View convertView, ViewGroup parent) {
            ValueItem item = (ValueItem)getItem(position);
           
            ViewHolder holder =null;
           if (convertView == null) {
                convertView = inflater.inflate(R.layout.row, null);
               
                holder = new ViewHolder();
                holder.chkbox = (CheckBox)convertView.findViewById(R.id.checkBox1);
                holder.txtview = (TextView)convertView.findViewById(R.id.textView1);
                holder.button = (Button)convertView.findViewById(R.id.button1);
                convertView.setTag(holder);
            }
            else {
                holder = (ViewHolder)convertView.getTag();
            }
           
            holder.chkbox.setChecked(item.isChecked());
            holder.txtview.setText(item.getTextmsg());

            return convertView;

        }
    }
   
    static class ViewHolder {
        CheckBox chkbox;
        TextView txtview;
        Button button;
    }
}

********************　　ValueItem.java　　********************
package jp.lesson.studyandroid;

public class ValueItem {

    private String strmsg = "";
   
    public boolean isChecked() {
        return true;
    }

    public CharSequence getTextmsg() {

        return strmsg;
    }

    public void setMsg(String string) {

        this.strmsg = string;
    }

}

********************　　activity_main.java　　********************

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/LinearLayout1"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <ListView

        android:id="@+id/android:list"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" >
    </ListView>

    <TextView

        android:id="@+id/android:empty"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="empty" />

</LinearLayout>