使用 AsyncTaskLoader 加载 JSON 时冻结 UI

Question

我想从本地数据库加载一些数据，为此我正在使用 AsynctaskLoader。但是在加载数据时，我无法与屏幕交互。整个 UI 冻结。我做了一些研究，发现应该在工作线程上初始化 AsyncTaskLoader 以将整个进程移动到工作线程上，我也尝试过这样做，但我再次得到冻结在 UI 中。

这是我的 AsyncTaskLoader 类

public class ArticleDatabaseLoader extends AsyncTaskLoader<List<Article>> {

private int code = 0;

public ArticleDatabaseLoader(Context context, int code) {
    super(context);
    this.code = code;
}

@Override
public List<Article> loadInBackground() {
    List<Article> articleList = new ArrayList<>();
    ArticleTable articleTable = new ArticleTable(getContext());
    ArticleCategory categoryTable = new ArticleCategory(getContext());
    switch (code) {
        case ArticleList:
            articleTable.open();
            categoryTable.open();
            List<String> selected_category = new ArrayList<>();
            for (int i = 0; i < 5; i++) {   /* saving all the selected categories */
                if (getCategoryStatus(getContext(), categories[i]) == 1) {
                    selected_category.add(categories[i]);
                }
            }
            StringBuilder where_query =  new StringBuilder();
            if (selected_category.size() > 0){  /* building the where query for sql */
                for (int i = 0; i < selected_category.size(); i++) {
                    if (i == selected_category.size() - 1) {
                        where_query.append(String.format("%s = '%s'",
                                DBColumn.ArticleCategoryColumn.category_id,
                                selected_category.get(i)));
                    } else {
                        where_query.append(String.format("%s = '%s' OR ",
                                DBColumn.ArticleCategoryColumn.category_id,
                                selected_category.get(i)));
                    }
                }
                Cursor selectedCursor = categoryTable.getArticles(where_query.toString());
                if (selectedCursor != null && selectedCursor.moveToFirst() && selectedCursor.getCount() > 0) {
                    do {
                        String articleId = selectedCursor.getString(selectedCursor.getColumnIndex(DBColumn.ArticleCategoryColumn.article_id));
                        Cursor articleCursor = articleTable.getArticleById(articleId);
                        if (articleCursor != null && articleCursor.moveToFirst()) {
                            articleList.add(articleTable.articleObject(getContext(),articleCursor));
                        }
                        articleCursor.close();
                    } while (selectedCursor.moveToNext());
                }
                if (selectedCursor != null)
                    selectedCursor.close();
            } else {
                Cursor articleListCursor = articleTable.getAllArticles();
                if (articleListCursor != null && articleListCursor.moveToFirst() && articleListCursor.getCount() > 0) {
                    do {
                        articleList.add(articleTable.articleObject(getContext(),articleListCursor));
                    } while (articleListCursor.moveToNext());
                }
                if (articleListCursor != null)
                    articleListCursor.close();
            }
            articleTable.close();
            categoryTable.close();
            return articleList;
    }

    return null;
}
}

这是我的 onCreateMethod

@Override
protected void onCreate(@Nullable final Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    ArticleTable articleTable = new ArticleTable(this);
    articleTable.open();
    if (articleTable.getAllArticles() != null) {
        /* load the data from local database */
        getSupportLoaderManager().initLoader(Loader_ID, null, ArticleListActivity.this).forceLoad();
    } else {
        ApiManager.getArticles(this, this);
    }
    articleTable.close();
}

Answer 1

完成设置后，创建异步任务以从数据库加载数据 适配器

MainActivity execute asynctask in oncreate and set adapter in call back method

public class MainActivity extends AppCompatActivity implements
 ArticleDatabaseLoader.ArticleDatabaseLoaderHandler{
{
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        new ArticleDatabaseLoader(MainActivity.this,0).execute();
    }

    @Override
    public void ArticleDatabaseLoaderComplete(List<Article> articleList) {
        if(articleList.size() > 0)
        {
            // refresh your adapter
        }
    }
}

创建 ArticleDatabaseLoader 类

import android.content.Context;
import android.database.Cursor;
import android.os.AsyncTask;

import java.util.ArrayList;
import java.util.List;


public class ArticleDatabaseLoader extends AsyncTask<String, String, String> {
    private int code = 0;
    List<Article> articleList = new ArrayList<>();
    protected Context mCtx;
    ArticleDatabaseLoaderHandler handler;
    public interface ArticleDatabaseLoaderHandler {
        void ArticleDatabaseLoaderComplete(List<Article> articleList);
    }

    public ArticleDatabaseLoader(Context context, int code) {
        mCtx = context;
        this.code = code;
        this.handler = (ArticleDatabaseLoaderHandler) context;
    }
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // todo display progress bar
    }
    @Override
    protected String doInBackground(String... strings) {
        ArticleTable articleTable = new ArticleTable(mCtx);
        ArticleCategory categoryTable = new ArticleCategory(mCtx);
        switch (code) {
            case ArticleList:
                articleTable.open();
                categoryTable.open();
                List<String> selected_category = new ArrayList<>();
                for (int i = 0; i < 5; i++) {   /* saving all the selected categories */
                    if (getCategoryStatus(mCtx, categories[i]) == 1) {
                        selected_category.add(categories[i]);
                    }
                }
                StringBuilder where_query = new StringBuilder();
                if (selected_category.size() > 0) {  /* building the where query for sql */
                    for (int i = 0; i < selected_category.size(); i++) {
                        if (i == selected_category.size() - 1) {
                            where_query.append(String.format("%s = '%s'",
                                    DBColumn.ArticleCategoryColumn.category_id,
                                    selected_category.get(i)));
                        } else {
                            where_query.append(String.format("%s = '%s' OR ",
                                    DBColumn.ArticleCategoryColumn.category_id,
                                    selected_category.get(i)));
                        }
                    }
                    Cursor selectedCursor = categoryTable.getArticles(where_query.toString());
                    if (selectedCursor != null && selectedCursor.moveToFirst() && selectedCursor.getCount() > 0) {
                        do {
                            String articleId = selectedCursor.getString(selectedCursor.getColumnIndex(DBColumn.ArticleCategoryColumn.article_id));
                            Cursor articleCursor = articleTable.getArticleById(articleId);
                            if (articleCursor != null && articleCursor.moveToFirst()) {
                                articleList.add(articleTable.articleObject(mCtx, articleCursor));
                            }
                            articleCursor.close();
                        } while (selectedCursor.moveToNext());
                    }
                    if (selectedCursor != null)
                        selectedCursor.close();
                } else {
                    Cursor articleListCursor = articleTable.getAllArticles();
                    if (articleListCursor != null && articleListCursor.moveToFirst() && articleListCursor.getCount() > 0) {
                        do {
                            articleList.add(articleTable.articleObject(getContext(), articleListCursor));
                        } while (articleListCursor.moveToNext());
                    }
                    if (articleListCursor != null)
                        articleListCursor.close();
                }
                articleTable.close();
                categoryTable.close();

                return null;

        }
    }
    protected void onPostExecute(String results) {
        // todo dismiss progress bar
        handler.ArticleDatabaseLoaderComplete(articleList);
    }
}