Question

我在android.developer.com上阅读了关于“使ListView滚动平滑”的文章，但有一点我不明白：放置或获取“位置”的值，因为我的eclipse说：“不能参考到在不同方法中定义的内部类中的非最终变量位置“。我把这段代码放在getView方法的适配器类中。

package com.example.filemanager;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Formatter.BigDecimalLayoutForm;

import android.content.Context;
import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.drawable.Drawable;
import android.os.AsyncTask;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.webkit.DateSorter;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.ProgressBar;
import android.widget.TextView;

public class ItemAdapter extends ArrayAdapter<Item> {
private final Context context;
private final ArrayList<Item> values;
public int position;

public ItemAdapter(Context context, ArrayList<Item> values) {
    super(context, R.layout.item, values);
    this.context = context;
    this.values = values;
}

@Override
public Item getItem(int position) {
    // TODO Auto-generated method stub
    return super.getItem(position);
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    // TODO Auto-generated method stub



    LayoutInflater inflater = (LayoutInflater) context
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View rowView = inflater.inflate(R.layout.item, parent, false);
    TextView title = (TextView) rowView.findViewById(R.id.title);
    TextView info = (TextView) rowView.findViewById(R.id.info);
    ImageView icon = (ImageView) rowView.findViewById(R.id.icon);
    ImageView menu = (ImageView) rowView.findViewById(R.id.menu);

    title.setText(values.get(position).getName());
    info.setText(sizeString(position) + " " + dateString(position) + " "
            + rightsString(position));

    if (values.get(position).isisDir()) {
        icon.setImageResource(R.drawable.dir);
    } else if (!values.get(position).isisDir()) {

        if (values.get(position).getPath().endsWith(".jpg")
                || values.get(position).getPath().endsWith(".png")) {

            final BitmapFactory.Options options = new BitmapFactory.Options();
            options.inSampleSize = 50;
            options.inDensity = 100;
            options.inScreenDensity = 1;

            Bitmap myBitmap = BitmapFactory.decodeFile(values.get(position).getPath(), options);                
            icon.setImageBitmap(myBitmap);
        }else{

            icon.setImageResource(R.drawable.file);
        }

    }

    menu.setImageResource(R.drawable.menu);



    ViewHolder holder = new ViewHolder();
    holder.icon = (ImageView) convertView.findViewById(R.id.icon);
    holder.menu = (ImageView) convertView.findViewById(R.id.menu);
    holder.title = (TextView) convertView.findViewById(R.id.title);
    holder.info = (TextView) convertView.findViewById(R.id.info);
    holder.progress = (ProgressBar) convertView.findViewById(R.id.progressSpinner);
    convertView.setTag(holder);



    // Using an AsyncTask to load the slow images in a background thread
            new AsyncTask<ViewHolder, Void, Bitmap>() {
                private ViewHolder v;

                @Override
                protected Bitmap doInBackground(ViewHolder... params) {
                    v = params[0];
                    //return mFakeImageLoader.getImage();



                    return null;
                }

                @Override
                protected void onPostExecute(Bitmap result) {
                    super.onPostExecute(result);
                    if (v.position == position) {
                        // If this item hasn't been recycled already, hide the
                        // progress and set and show the image
                        v.progress.setVisibility(View.GONE);
                        v.icon.setVisibility(View.VISIBLE);
                        v.icon.setImageBitmap(result);
                    }
                }
            }.execute(holder);






    return rowView;
}

private String rightsString(int position) {
    String temp = "";
    if (values.get(position).isReadable()) {
        temp += "r";
    } else {
        temp += "-";
    }
    if (values.get(position).isWritable()) {
        temp += "w";
    } else {
        temp += "-";
    }
    if (values.get(position).isExecutable()) {
        temp += "x";
    } else {
        temp += "-";
    }
    return temp;
}

private String dateString(int position) {
    DateFormat df = new SimpleDateFormat("MM/dd/yyyy HH:mm:ss");
    return df.format(values.get(position).getDate());
}

private String sizeString(int position) {

    long bytes = values.get(position).getSize();

    double kb = bytes / 1024.0;
    double mb = kb / 1024.0;
    double gb = mb / 1024.0;

    if (gb >= 1) {
        return gb + " GB";
    }
    if (mb >= 1) {
        return mb + " MB";
    }
    if (kb >= 1) {
        return kb + " KB";
    } else {
        return bytes + " bytes";
    }

}


static class ViewHolder {

    ImageView icon, menu;
    TextView title, info;
    ProgressBar progress;
    int position;

}

}

Answer 1

好的，所以你需要了解一下外部，内部和匿名类等。发生的事情是你正在创建一个带有

声明的匿名类

new AsyncTask()....

并且该类内部的任何变量都必须是final或不引用父类。

所以，你需要做的是：

final int finalPosition = position;


// Using an AsyncTask to load the slow images in a background thread
    new AsyncTask() {
    private ViewHolder v;

    @Override
    protected Bitmap doInBackground(ViewHolder... params) {
       v = params[0];
       return null;
    }

    @Override
    protected void onPostExecute(Bitmap result) {
       super.onPostExecute(result);
       if (v.position == finalPosition) {
           // If this item hasn't been recycled already, hide the
           // progress and set and show the image
           v.progress.setVisibility(View.GONE);
           v.icon.setVisibility(View.VISIBLE);
           v.icon.setImageBitmap(result);
           }
        }
    }.execute(holder);

Reference

使ListView滚动平滑位置？

1 个答案: