Question

我有FirstscreenActivity，其中我使用RecyclerView，（在此RecyclerView中显示由用户创建的项目的图片），然后用户转到下一个Activity，在那里他创建新项目并在那里添加图片。当用户返回到FirstScreenActivity时，旧项目会再次下载，然后再下载新项目。如何让旧项目在更改活动后不再下载一次（因此不会重复）？

public class FirstscreenActivity extends AppCompatActivity implements RecyclerItemClickListener.OnItemClickListener {

    private MyAdapter mAdapter;
    private LinearLayoutManager mLayoutManager;
    public static String mCurrentProject = null;

    RecyclerView list;

    static File[] listFile;
    static File[] listFolders;

    static int newpressed = 0;

    public static ArrayList<Folder> FOLDERS = new ArrayList<>();
    public static LruCache<String, Bitmap> mMemoryCache;

    public static File[] listFile2;


    public void getFromSdcardFolders() {
        File file = new File(Environment.getExternalStorageDirectory() +
                "/Audio_Recorder_Picture", "Previews");
        if (file.isDirectory()) {
            listFolders = file.listFiles();
            for (int i = 0; i < listFolders.length; i++) {

                Folder folderobject = new Folder();
                folderobject.setName(listFolders[i].getName());
                Log.i("List of FOLDERS: ", String.valueOf(listFolders[i].getName()));

                File picturelist = new File(Environment.getExternalStorageDirectory() +
                        "/Audio_Recorder_Picture/Previews", listFolders[i].getName());
                if (picturelist.isDirectory()) {
                    listFile = picturelist.listFiles();
                    for (int j = 0; j < listFile.length; j++) {
                        folderobject.addFile(listFile[j].getAbsolutePath());
                    }
                }
                FOLDERS.add(folderobject);
                Log.wtf("TAG", "Folders size inside the getFRom:" + FOLDERS.size());
            }
        }
    }


    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.front);
        Toolbar myToolbar = (Toolbar) findViewById(R.id.my_toolbar);
        setSupportActionBar(myToolbar);
        getSupportActionBar().setTitle("");

        list = (RecyclerView) findViewById(R.id.list);

        list.setHasFixedSize(true);

        mLayoutManager = new LinearLayoutManager(getApplicationContext());
        mLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
        list.addOnItemTouchListener(new RecyclerItemClickListener(this, this));

        getFromSdcardFolders();

        list.setLayoutManager(mLayoutManager);

        mAdapter = new MyAdapter(this, FOLDERS);
        list.setAdapter(mAdapter);
        mAdapter.notifyDataSetChanged();

        final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);

        // Use 1/8th of the available memory for this memory cache.
        final int cacheSize = maxMemory / 4;

        mMemoryCache
                = new LruCache<String, Bitmap>(cacheSize) {
            @Override
            protected int sizeOf(String key, Bitmap bitmap) {
                // The cache size will be measured in kilobytes rather than
                // number of items.
                return bitmap.getByteCount() / 1024;
            }
        };
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        getMenuInflater().inflate(R.menu.menu, menu);
        return super.onPrepareOptionsMenu(menu);
    }


    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.addItem:
                SimpleDateFormat formatter = new SimpleDateFormat("yyyy_MM_dd_hh_mm_ss");
                Date now = new Date();
                mCurrentProject = String.valueOf(formatter.format(now));
                Log.d("newpressed: ", String.valueOf(newpressed));
                Intent nextScreen = new Intent(getApplicationContext(), AudioRecord.class);
                startActivity(nextScreen);
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }

    @Override
    public void onItemClick(View childView, int position) {

        File picturelist2 = new File(Environment.getExternalStorageDirectory() +
                "/Audio_Recorder_Picture/Pictures", listFolders[position].getName());
        if (picturelist2.isDirectory()) {
            listFile2 = picturelist2.listFiles();
            for (int i = 0; i < listFile2.length; i++) {
                Log.i("LIST OF PICTURES: ", String.valueOf(listFile2[i]));
            }

        }
        Intent viewScreen = new Intent(getApplicationContext(), ViewActivity.class);
        viewScreen.putExtra("FILE_TAG", listFile2);
        startActivity(viewScreen);
    }

    @Override
    public void onItemLongPress(View childView, int position) {

    }
}

适配器代码：

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder>` {

    public final Activity context;
    public final ArrayList<Folder> FOLDERS;
    View view;

    public long getItemId(int position) {
        return position;
    }

    @Override
    public int getItemCount() {
        Log.wtf("TAG", "Folders size: " + FOLDERS.size());
        return FOLDERS.size();
    }

    // optimisation of bitmap

    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 decodeSampledBitmapFromResource(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);
    }

    public void loadBitmap(String path, ImageView imageView, int position) {
        final String imageKey = String.valueOf(path);

        Bitmap bitmap = getBitmapFromMemCache(imageKey);
        if (bitmap != null) {
            imageView.setImageBitmap(bitmap);
        } else {

            bitmap = decodeSampledBitmapFromResource(path, 100, 100);
            imageView.setImageBitmap(bitmap);
           // BitmapWorkerTask task = new BitmapWorkerTask(imageView, position);
           // task.execute(path);
        }
    }


    public static class ViewHolder extends RecyclerView.ViewHolder {
        public TextView mTextView;
        public TextView title;
        public ImageView image1;
        ImageView image2;
        ImageView image3;
        ImageView image4;
        ImageView image5;
        TextView slides;

        public ViewHolder(View v) {
            super(v);
            title = (TextView) v.findViewById(R.id.item);
            image1 = (ImageView) v.findViewById(R.id.icon1);
            image2 = (ImageView) v.findViewById(R.id.icon2);
            image3 = (ImageView) v.findViewById(R.id.icon3);
            image4 = (ImageView) v.findViewById(R.id.icon4);
            image5 = (ImageView) v.findViewById(R.id.icon5);
            slides = (TextView) v.findViewById(R.id.textView1);

        }
    }

    public MyAdapter(Activity context, ArrayList<Folder> FOLDERS) {
        this.context = context;
        this.FOLDERS = FOLDERS;
        getItemCount();
    }

    @Override
    public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent,
                                                   int viewType) {

        Log.wtf("TAG", "OnCreateViewHolder works!!!");
        view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.mylist, parent, false);
        ViewHolder vh = new ViewHolder(view);
        return vh;
    }


    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        Folder folder = FOLDERS.get(position);

        holder.image1.setImageResource(R.drawable.placeholder);
        holder.image2.setImageResource(R.drawable.placeholder);
        holder.image3.setImageResource(R.drawable.placeholder);
        holder.image4.setImageResource(R.drawable.placeholder);
        holder.image5.setImageResource(R.drawable.placeholder);

        ArrayList<String> imgs = folder.getPicturelist();

        holder.title.setText(folder.getName());

        BitmapFactory.Options options = new BitmapFactory.Options();
        options.inPreferredConfig = Bitmap.Config.RGB_565;
        options.inSampleSize = 10;


        for (int i = 0; i < 5; i++) {
            switch (i) {
                case 0:
                    if (imgs.size() > i && imgs.size() != 0) {
                        loadBitmap(imgs.get(i), holder.image1, position);
                    } else {
                        holder.image1.setImageBitmap(null);
                        // holder.image1.setImageResource(R.drawable.placeholder);
                    }
                    break;
                case 1:
                    if (imgs.size() > i && imgs.size() != 0) {
                        loadBitmap(imgs.get(i), holder.image2, position);
                    } else {
                        holder.image2.setImageBitmap(null);
                        // holder.image2.setImageResource(R.drawable.placeholder);
                    }
                    break;
                case 2:
                    if (imgs.size() > i && imgs.size() != 0) {
                        loadBitmap(imgs.get(i), holder.image3, position);
                    } else {
                        holder.image3.setImageBitmap(null);
                        // holder.image3.setImageResource(R.drawable.placeholder);
                    }
                    break;
                case 3:
                    if (imgs.size() > i && imgs.size() != 0) {
                        loadBitmap(imgs.get(i), holder.image4, position);
                    } else {
                        holder.image4.setImageBitmap(null);
                        // holder.image4.setImageResource(R.drawable.placeholder);
                    }
                    break;
                case 4:
                    if (imgs.size() > i && imgs.size() != 0) {
                        loadBitmap(imgs.get(i), holder.image5, position);
                    } else {
                        holder.image5.setImageBitmap(null);
                        // holder.image5.setImageResource(R.drawable.placeholder);
                    }
                    break;
            }
        }

        holder.slides.setText("Количество слайдов: " + imgs.size());
        view.setTag(holder);
    }

    public Bitmap getBitmapFromMemCache(String key) {
        return com.example.attracti.audiorecorderpicture.FirstscreenActivity.mMemoryCache.get(key);

    }
}

的AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.myproject">

    <uses-permission android:name="android.permission.CAMERA"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.RECORD_AUDIO" />
    <uses-feature android:name="android.hardware.camera" />


    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/Theme.AppCompat.Light.NoActionBar"
        android:name=".model.App"
        >

        <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

        <activity android:name=".activities.AudioRecord"
            android:screenOrientation="portrait"
            android:configChanges="orientation|keyboardHidden">
        </activity>
        <activity android:name=".activities.FirstscreenActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".activities.ViewActivity">
    </activity>
    </application>

</manifest>

Answer 1

解决方案

如果您使用 intent 返回第一个活动，它将按预期再次创建活动。为防止这种情况，您可以将其添加到清单：

<activity android:name=".activities.FirstscreenActivity"
          android:launchMode= "singleInstance"
          ...

singleInstance只会创建一次活动。

解决方案

如果您想返回，请使用finish()。

更新RecyclerView中的数据

1 个答案: