用于图像获取的AsyncTask不断被调用

Question

我有一个小应用程序来保存学生名单。

添加新学生记录时，从我自己的10个地址池中选择一个随机图像URL（字符串），使用AsyncTask在图像视图中提取和设置。

我使用自定义CursorAdapter作为列表，并使用自定义SQLiteOpenHelper DB来处理数据库（包含id，name，grade，image url str）。

我正在使用AsyncTask来从互联网上获取图像

我的问题是我的AsyncTask不断被一遍又一遍地调用，每次点击屏幕时，都会获取之前已经获取的相同图像。

我想我正在使用我的AsyncTask错误（通过bindView），但不确定。

我的目标是只为每一行获取一次图像

主要内容：

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    /* Fields for adding new student to the list */
    private EditText mEtName;
    private EditText mEtGrade;
    private ListView mLvStudents;

    /* Our DB model to store student objects */
    private SqlDbHelper mDB;

    /* Custom SQL-Adapter to connect our SQL DB to the ListView */
    private SQLAdapter mAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        /* Init fields & needed views */
        mEtName = findViewById(R.id.et_name);
        mEtGrade = findViewById(R.id.et_grade);
        mLvStudents = findViewById(R.id.lv_students);
        mDB = new SqlDbHelper(getApplicationContext());
        mAdapter = new SQLAdapter(this, mDB.getAllRows(), false);

        /* Set click listeners and adapter to our list */
        mLvStudents.setAdapter(mAdapter);
        findViewById(R.id.button_add).setOnClickListener(this);
    }

    @Override
    public void onClick(View view) {
        final String name = mEtName.getText().toString();
        final int gradeInt = AidUtils.getGradeInt(mEtGrade.getText().toString());

        mDB.addStudent(name, gradeInt, AidUtils.randImageUrl());
        mAdapter.changeCursor(mDB.getAllRows());
        mEtName.setText("");
        mEtGrade.setText("");
    }
}

SQLAdapter：

final class SQLAdapter extends CursorAdapter {
    private LayoutInflater mInflater;

    public SQLAdapter(Activity context, Cursor c, boolean autoRequery) {
        super(context, c, autoRequery);
        mInflater = LayoutInflater.from(context);
    }

    @Override
    public View newView(Context context, Cursor cursor, ViewGroup viewGroup) {
        return mInflater.inflate(R.layout.lv_line, viewGroup, false);
    }

    @Override
    public void bindView(final View view, Context context, Cursor cursor) {
        /* Set name */
        ((TextView)view.findViewById(R.id.tv_name)).setText(
                cursor.getString(cursor.getColumnIndex(SqlDbHelper.KEY_NAME)));

        /* Set the image URL for it and fetch the image */
        final String imageUrlStr = cursor.getString(cursor.getColumnIndex(SqlDbHelper.KEY_IMG));
        ((TextView)view.findViewById(R.id.tv_image_url)).setText(imageUrlStr);

        new AsyncImageSet(imageUrlStr, (ImageView)view.findViewById(R.id.iv_pic)).execute();

        /* Set grade and color for it */
        final int grade = cursor.getInt(cursor.getColumnIndex(SqlDbHelper.KEY_GRADE));
        ((TextView)view.findViewById(R.id.tv_grade)).setText(String.valueOf(grade));
    }
}

SqlDbHelper：

final class SqlDbHelper extends SQLiteOpenHelper {
    private static final String TAG = "SqlDbHelper";

    /* Database version */
    public static final int VERSION = 1;

    /* Relevant string names, keys represent columns */
    public static final String DB_NAME = "StudentsDB";
    public static final String TABLE_NAME = "students";
    public static final String KEY_ID = "_id";
    public static final String KEY_NAME = "Name";
    public static final String KEY_GRADE = "Grade";
    public static final String KEY_IMG = "Image";

    public SqlDbHelper(Context context) {
        super(context, DB_NAME, null, VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
        StringBuilder createQuery = new StringBuilder();
        createQuery.append("CREATE TABLE " + TABLE_NAME + " (")
                .append(KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT,")
                .append(KEY_NAME + " TEXT,")
                .append(KEY_GRADE + " INT,")
                .append(KEY_IMG + " TEXT")
                .append(")");

        Log.d(TAG, "Create table query: " + createQuery.toString());
        sqLiteDatabase.execSQL(createQuery.toString());
    }

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {}

    public void addStudent(final String name, final int grade, final String imageUrl) {
        ContentValues cv = new ContentValues();
        cv.put(KEY_NAME, name);
        cv.put(KEY_GRADE, grade);
        cv.put(KEY_IMG, imageUrl);
        getWritableDatabase().insert(TABLE_NAME, null, cv);
    }

    public Cursor getAllRows() {
        return (getReadableDatabase().
                rawQuery("SELECT * FROM " + TABLE_NAME, null));
    }
}

AsyncImageSet：

public class AsyncImageSet extends AsyncTask<Void, Void, Bitmap> {
    private String mImageUrl;
    private ImageView mImageView;

    public AsyncImageSet(String imageUrl, ImageView imageView) {
        mImageUrl = imageUrl;
        mImageView = imageView;
    }

    @Override
    protected Bitmap doInBackground(Void... voids) {
        Log.v("AsyncImageSet", "New Async Task launched!");
        Bitmap image = null;
        try {
            image = AidUtils.getBitmapFromUrl(AidUtils.buildUrl(mImageUrl));
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            return image;
        }
    }

    @Override
    protected void onPostExecute(Bitmap image) {
        if(image != null) {
            mImageView.setImageBitmap(image);
        }
    }
}

我在这做错了什么？

谢谢

Answer 1

另一答案