GridView 位图图像在刷新时翻倍

Question

我正在关注此Android tutorial 以修复在我的GridView 中使用Bitmap 图像时不断出现的“内存不足”错误。本教程解决了这个问题，但是现在当我单击活动中的其他选项卡时，然后返回到我的照片选项卡，那里的照片会翻倍。例如，当我第一次加载选项卡时，它会从我的 SD 卡中提取 3 张照片，并用占位符图像填充其余部分。但是当我浏览其他标签（总共 4 个）时，我回来在我的照片标签 GridView 中找到 6 张图片，其余的都是占位符。

背景信息：每次我的标签可见时，它都会从 SD 卡加载图像，将它们更改为位图，然后我的适配器将这些图像放入 GridView 内的每个 ImageView 中。在我遇到内存问题之前，它加载得很好，当我浏览其他选项卡然后回到照片选项卡时，它没有加倍图像。然而，它最终确实因内存问题而崩溃，所以我不得不修复它。

如何在刷新标签时不加载双倍？感谢您的帮助。

PhotoTab.java

package org.azurespot.cutecollection;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.os.Environment;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.GridView;

import org.azurespot.R;

import java.io.File;
import java.util.ArrayList;

/**
 * Created by mizu on 2/8/15.
 */
public class PhotoTab extends Fragment {

    private GridView gridView;
    File[] files;
    ArrayList<PhotoGridItem> photoList = new ArrayList<>();
    ArrayAdapter<PhotoGridItem> adapter;
    Bitmap bitmap;

    public PhotoTab() {
        super();
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        // Inflate the layout for this fragment
        View v = inflater.inflate(R.layout.photo_tab, container, false);

        // with fragments, make sure you include the rootView when finding id
        gridView = (GridView) v.findViewById(R.id.photo_grid);
        adapter = new GridViewPhotoAdapter(getActivity(), R.layout.photo_grid_item);
        // Set the Adapter to GridView
        gridView.setAdapter(adapter);
        adapter.addAll(loadSDCard());

        // add the default icons remaining, to GridView, if less than 24 files on SD card
        for (int i = 0; i < (24 - photoList.size()); i++) {

            adapter.add(new PhotoGridItem(BitmapFactory.decodeResource(getResources(),
                    R.drawable.ic_photo_placeholder)));

        }

        adapter.notifyDataSetChanged();

        return v;
    }

    private ArrayList<PhotoGridItem> loadSDCard() {

        try {
            // gets directory CutePhotos from sd card
            File cutePhotosDir = new File(Environment.getExternalStoragePublicDirectory
                    (Environment.DIRECTORY_PICTURES), "CutePhotos");
            // lists all files in CutePhotos, loads in Files[] array
            files = cutePhotosDir.listFiles();

            for (File singleFile : files) {
                String filePath = singleFile.getAbsolutePath();

                bitmap = decodeSampledBitmap(filePath, 270, 270);

                photoList.add(new PhotoGridItem(bitmap));
            }

        } catch (Exception e) {
            e.printStackTrace();
        }

        return photoList;
    }

    public static int calculateInSampleSize(
            BitmapFactory.Options options, int reqWidth, int reqHeight) {
        // Raw height and width of image
        final int height = options.outHeight;
        final int width = options.outWidth;
        int inSampleSize = 1;

        if (height > reqHeight || width > reqWidth) {

            final int halfHeight = height / 2;
            final int halfWidth = width / 2;

            // Calculate the largest inSampleSize value that is a power of 2 and keeps both
            // height and width larger than the requested height and width.
            while ((halfHeight / inSampleSize) > reqHeight
                    && (halfWidth / inSampleSize) > reqWidth) {
                inSampleSize *= 2;
            }
        }

        return inSampleSize;
    }

    public static Bitmap decodeSampledBitmap(String path, int reqWidth, int reqHeight) {

        // First decode with inJustDecodeBounds=true to check dimensions
        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        BitmapFactory.decodeFile(path, options);

        // Calculate inSampleSize
        options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

        // Decode bitmap with inSampleSize set
        options.inJustDecodeBounds = false;

        return BitmapFactory.decodeFile(path, options);
    }
}

GridViewPhotoAdapter

package org.azurespot.cutecollection;

/**
* Created by mizu on 2/5/15.
*/
// package org.azurespot.cutecollection;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.LinearLayout;

import org.azurespot.R;

/**
 * Created by mizu on 2/5/15.
 */
public class GridViewPhotoAdapter extends ArrayAdapter<PhotoGridItem> {

    public Context context;
    private int resourceId;
    Bitmap bm;

    public GridViewPhotoAdapter(Context context, int layoutResourceId) {
        super(context, layoutResourceId);
        this.context = context;
        this.resourceId = layoutResourceId;
    }

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

        View row = convertView;
        final ViewHolder holder;

        if (row == null) {

            LayoutInflater inflater = ((Activity) context).getLayoutInflater();
            row = inflater.inflate(resourceId, parent, false);

            holder = new ViewHolder();
            holder.imageView = (ImageView) row.findViewById(R.id.photo_grid_view);
            // stores holder with view
            row.setTag(holder);

        } else {

            holder = (ViewHolder)convertView.getTag();
        }

        PhotoGridItem photoGridItem = getItem(position);

        if (photoGridItem != null) {
            bm = photoGridItem.getImage();
            holder.imageView.setImageBitmap(bm);

            // positioning the image in the GridView slot
            holder.imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
            holder.imageView.setLayoutParams(new LinearLayout.LayoutParams
                    (270, 270));
        }

        return row;

    }

    public class ViewHolder{
        ImageView imageView;
    }
}

Answer 1

试试这个：

adap = null;
if (adap == null) {

                            adap = new Grid_View_Adatper(activity, arrayList);
                            gridView.setAdapter(adap);

                        }
                        adap.notifyDataSetChanged();