Question

无法想出这个，我搜索了很多。无法模拟我的任何测试设备上的错误，但偶尔会发生在我的某些用户身上。

我有一个自定义列表视图适配器，从在线数据库中提取了6个项目并添加到列表中。我还在列表的底部添加了一个额外的静态页脚。

据我所知，当发生此错误时，listview中没有任何内容，它为0，因此app无法获取位置 - 因为从在线数据库中拉出字符串。

我试图通过if / else但仍然得到indexoutofbounds错误来解决这个问题。在线：

if(mCategoryAdapter.getItem(position)!=null)

或

Category category = mCategoryAdapter.getItem(position);

我的问题是 - 我假设用户在完全填充之前点击了列表？有什么想法如何制止这个？

public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    //assigning XML view
    setContentView(R.layout.activity_category);

    //fill the list view from data from parse.com using custom CategoryAdapter
    mCategoryAdapter = new CategoryAdapter(this, new ArrayList<Category>());
    //assigning ListView to XML ListView
    mListView = (ListView)findViewById(R.id.category_list);
    mListView.setAdapter(mCategoryAdapter);
    customExercisesView = getLayoutInflater().inflate(R.layout.category_custom_exercises_row_item,mListView,false);

    //make items in list clickable
    mListView.setOnItemClickListener(this);
    //parse query to retrieve the categories
    getCategoryList();
}

public void getCategoryList()
{

    //parse query to pull all the current available exercises from the db
    ParseQuery<Category> query = ParseQuery.getQuery(Category.class).fromLocalDatastore();
    //call to parse.com to start the query
    query.findInBackground(new FindCallback<Category>() {
        @Override
        public void done(List<Category> categories, ParseException error) {
            if(categories !=null)
            {
                //add all the categories into the list
                mCategoryAdapter.addAll(categories);
                //add the custom exercises footer after we have added the rest
                mListView.addFooterView(customExercisesView);
                //sort the list alphabetically
                mCategoryAdapter.sort(new Comparator<Category>() {
                    @Override
                    public int compare(Category category, Category t1) {
                        return category.getName().compareTo(t1.getName());
                    }
                });
            }
        }
    });
}


 @Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
    //to make phone vibrate for 20 milliseconds when clicking an item in the list
    Vibrator v = (Vibrator) this.getApplicationContext().getSystemService(Context.VIBRATOR_SERVICE);
    v.vibrate(20);
    //users are selecting one of the 6 main exercise categories
    if(position<=5) {
        if(mCategoryAdapter.getItem(position)!=null) {
            //giving the listed exercises in the list view the ability to be clicked on
            Category category = mCategoryAdapter.getItem(position);
            //Get category ID and name to pass to Exercise List
            mCategoryID = category.getObjectId();
            mCategoryName = category.getName();
            Intent exercise_intent = new Intent(this, ExerciseList.class);
            exercise_intent.putExtra("categoryID", mCategoryID);
            exercise_intent.putExtra("categoryName", mCategoryName);
            startActivity(exercise_intent);
        }
        else
            Toast.makeText(this, "Categories are still loading, please try again", Toast.LENGTH_SHORT).show();
    }else
    {

                    //user is selecting custom exercises
                    Intent custom_exercise_intent = new Intent(this, CustomExerciseList.class);
                    startActivity(custom_exercise_intent);


    }

异常java.lang.IndexOutOfBoundsException：索引0无效， size is 0 java.util.ArrayList.throwIndexOutOfBoundsException （ArrayList.java:255)java.util.ArrayList.get（ArrayList.java:308） android.widget.ArrayAdapter.getItem（ArrayAdapter.java:337） adam.exercisedictionary.CategoryList.onItemClick（CategoryList.java:139） android.widget.AdapterView.performItemClick （AdapterView.java:308）android.widget.AbsListView.performItemClick （AbsListView.java:1154）android.widget.AbsListView $ PerformClick.run （AbsListView.java:3074）android.widget.AbsListView $ 3.run （AbsListView.java:3905）android.os.Handler.handleCallback （Handler.java:739）android.os.Handler.dispatchMessage （Handler.java:95）android.os.Looper.loop（Looper.java:135） android.app.ActivityThread.main（ActivityThread.java:5595） java.lang.reflect.Method.invoke（Method.java） java.lang.reflect.Method.invoke（Method.java:372） com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run （ZygoteInit.java:960）com.android.internal.os.ZygoteInit.main （ZygoteInit.java:755）

Answer 1

您是否检查过6个项目的数据集是空的还是在该代码点不可用？首先，检查并访问数据集中的单个项目。

我不知道它是否会起作用。试试看。 DB可能会返回空列表。

Answer 2

mCategoryAdapter = new CategoryAdapter(this, new ArrayList<Category>());

在此行中，您传递的ArrayList没有值，表示其大小为zero。在这里你必须通过已经填充了一些项目的ArrayList。赞：

List<Category> list = new ArrayList<Category>();
list.add(category1);
list.add(category2);
list.add(category3);
mCategoryAdapter = new CategoryAdapter(this, list);

Answer 3

非常感谢你们，

我明白了。我确定在用户点击并启动onclick方法时填写了列表视图。

我意识到我的查询是从本地数据存储区检索的，我在启动应用程序时加载了类别，同时显示了初始屏幕。问题是如果这些类别在启动时没有加载，那么此查询将无法从本地数据存储中检索。

解决方案是通过重新尝试从Internet检索值来处理本地数据存储区查询为空，并且解决了问题，此后没有崩溃。

用户连接到网络并下载类别后，无需再次连接，因为它们已永久固定在设备上。

    public void getCategoryList()
{
    //parse query to pull all the current available exercises from the db
    ParseQuery<Category> query = ParseQuery.getQuery(Category.class).fromLocalDatastore();
    //call to parse.com to start the query
    query.findInBackground(new FindCallback<Category>() {
        @Override
        public void done(List<Category> categories, ParseException error) {
            if(categories !=null)
            {
                mCategoryAdapter.clear();
                //add all the categories into the list
                mCategoryAdapter.addAll(categories);
            }
            else
            {
                //check we have internet
                if(DetectConnection.isConnected(getApplicationContext())) {
                    //backup get categories from net
                    getCategoryListFromParse();
                }
                else
                {
                    //no internet and issues getting categories, let user know
                    Toast.makeText(getApplicationContext(),"Please check your internet connection", Toast.LENGTH_SHORT).show();
                }
            }
        }
    });
}

 public void getCategoryListFromParse()
{
    //parse query to pull all the current available exercises from the db
    ParseQuery<Category> query = ParseQuery.getQuery(Category.class);
    //call to parse.com to start the query
    query.findInBackground(new FindCallback<Category>() {
        @Override
        public void done(List<Category> categories, ParseException error) {
            if(categories !=null)
            {
                Category.pinAllInBackground(categories);
                //add all the categories into the list
                mCategoryAdapter.addAll(categories);
            }
        }
    });
}

Android间歇性错误onitemclick java.lang.IndexOutOfBoundsException：索引0无效，大小为0

3 个答案: