当我尝试初始化一个 class 以调用其方法之一时，出现错误，如何解决？

Question

我正在制作一个需要自定义数组适配器的 android 应用程序。在此 class 中，扩展数组适配器由媒体播放器初始化组成。我在此 class 下创建了另一种方法，以便在与单词适配器相关联的 activity 停止后立即释放媒体播放器。当我在 activity 中创建停止方法并尝试初始化自定义数组适配器 class 时出现错误，提示 "Constructor cannot be applied to ()"，或者当我尝试 WordAdapter w=null 并调用该方法时我不想出错，但在运行时应用程序强制关闭！ 这是 activity 代码：

public class ColorsActivity extends AppCompatActivity {

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

    // Create a list of words
    ArrayList<Word> words = new ArrayList<Word>();
    words.add(new Word("red", "weṭeṭṭi",R.drawable.color_red,R.raw.color_red));
    words.add(new Word("mustard yellow", "chiwiiṭә",R.drawable.color_mustard_yellow,R.raw.color_mustard_yellow));
    words.add(new Word("dusty yellow", "ṭopiisә",R.drawable.color_dusty_yellow,R.raw.color_dusty_yellow));
    words.add(new Word("green", "chokokki",R.drawable.color_green,R.raw.color_green));
    words.add(new Word("brown", "ṭakaakki",R.drawable.color_brown,R.raw.color_brown));
    words.add(new Word("gray", "ṭopoppi",R.drawable.color_gray,R.raw.color_gray));
    words.add(new Word("black", "kululli",R.drawable.color_black,R.raw.color_black));
    words.add(new Word("white", "kelelli",R.drawable.color_white,R.raw.color_white));

    // Create an {@link WordAdapter}, whose data source is a list of {@link Word}s. The
    // adapter knows how to create list items for each item in the list.
    WordAdapter adapter = new WordAdapter(this, words,R.color.category_colors);

    // Find the {@link ListView} object in the view hierarchy of the {@link Activity}.
    // There should be a {@link ListView} with the view ID called list, which is declared in the
    // word_list.xml layout file.
    ListView listView = (ListView) findViewById(R.id.list);

    // Make the {@link ListView} use the {@link WordAdapter} we created above, so that the
    // {@link ListView} will display list items for each {@link Word} in the list.
    listView.setAdapter(adapter);
}

@Override
protected void onStop()
{
    WordAdapter w= new WordAdapter();
    w.terminate();
    super.onStop();


    // TODO: Implement this method

}

}

自定义适配器代码：

public class WordAdapter extends ArrayAdapter<Word> {
    int b;
    MediaPlayer mp;


    /**
     * Create a new {@link WordAdapter} object.
     *
     * @param context is the current context (i.e. Activity) that the adapter is being created in.
     * @param words is the list of {@link Word}s to be displayed.
     */
    private int mbgcolor;
    public WordAdapter(Context context, ArrayList<Word> words, int BgColor)
    {
        super(context, 0, words);
        mbgcolor = BgColor;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent)
    {
        // Check if an existing view is being reused, otherwise inflate the view
        View listItemView = convertView;
        if (listItemView == null)
        {
            listItemView = LayoutInflater.from(getContext()).inflate(
                R.layout.list_item, parent, false);
        }

        // Get the {@link Word} object located at this position in the list
        Word currentWord = getItem(position);

        // Find the TextView in the list_item.xml layout with the ID miwok_text_view.
        TextView miwokTextView = (TextView) listItemView.findViewById(R.id.miwok_text_view);
        // Get the Miwok translation from the currentWord object and set this text on
        // the Miwok TextView.
        miwokTextView.setText(currentWord.getMiwokTranslation());

        // Find the TextView in the list_item.xml layout with the ID default_text_view.
        TextView defaultTextView = (TextView) listItemView.findViewById(R.id.default_text_view);
        // Get the default translation from the currentWord object and set this text on
        // the default TextView.
        defaultTextView.setText(currentWord.getDefaultTranslation());
        // Find the ImageView in the list_item.xml layout with the ID list_item_icon

        if (currentWord.hasImage())
        {
            ImageView iconView = (ImageView) listItemView.findViewById(R.id.miwok_image_view);
            // Get the image resource ID from the current AndroidFlavor object and
            // set the image to iconView
            iconView.setImageResource(currentWord.getImageResourceId());
            iconView.setVisibility(View.VISIBLE);
        }
        else
        {
            ImageView iconView = (ImageView) listItemView.findViewById(R.id.miwok_image_view);
            iconView.setVisibility(View.GONE);

        }
        View text_container=listItemView.findViewById(R.id.text_container);
        int bgc=ContextCompat.getColor(getContext(), mbgcolor);
        text_container.setBackgroundColor(bgc);
        // Return the whole list item layout (containing 2 TextViews) so that it can be shown in
        // the ListView.
        int song= currentWord.getSongResourceId();
        mp=MediaPlayer.create(getContext(),song);
         text_container.setOnClickListener(new OnClickListener(){
             public void onClick(View v)
             {
                mp.start(); 

             }
         });

        return listItemView;

    }
    public void terminate()
    {
        mp.release();
    }
}

如何解决这个问题？

Answer 1

您每次都在 onStop 中实例化一个新的适配器，而不是使用现有的适配器。

ColorsActivity extends AppCompatActivity {

private WordAdapter mAdapter;

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

    // Create a list of words
    ArrayList<Word> words = new ArrayList<Word>();
    words.add(new Word("red", "weṭeṭṭi",R.drawable.color_red,R.raw.color_red));
    words.add(new Word("mustard yellow", "chiwiiṭә",R.drawable.color_mustard_yellow,R.raw.color_mustard_yellow));
    words.add(new Word("dusty yellow", "ṭopiisә",R.drawable.color_dusty_yellow,R.raw.color_dusty_yellow));
    words.add(new Word("green", "chokokki",R.drawable.color_green,R.raw.color_green));
    words.add(new Word("brown", "ṭakaakki",R.drawable.color_brown,R.raw.color_brown));
    words.add(new Word("gray", "ṭopoppi",R.drawable.color_gray,R.raw.color_gray));
    words.add(new Word("black", "kululli",R.drawable.color_black,R.raw.color_black));
    words.add(new Word("white", "kelelli",R.drawable.color_white,R.raw.color_white));

    // Create an {@link WordAdapter}, whose data source is a list of {@link Word}s. The
    // adapter knows how to create list items for each item in the list.
    mAdapter = new WordAdapter(this, words,R.color.category_colors);

    // Find the {@link ListView} object in the view hierarchy of the {@link Activity}.
    // There should be a {@link ListView} with the view ID called list, which is declared in the
    // word_list.xml layout file.
    ListView listView = (ListView) findViewById(R.id.list);

    // Make the {@link ListView} use the {@link WordAdapter} we created above, so that the
    // {@link ListView} will display list items for each {@link Word} in the list.
    listView.setAdapter(mAdapter);
}

@Override
protected void onStop()
{
    mAdapter.terminate();
    super.onStop();


    // TODO: Implement this method

}

}

Answer 2

首先，这与Android无关，这是一个通用的编程问题！

---

你的class(WordAdapter)的构造函数是这样定义的：

public WordAdapter(Context context, ArrayList<Word> words, int BgColor)
{
    super(context, 0, words);
    mbgcolor = BgColor;
}

问题是：

1- 你说错了！ WordAdapter w= new WordAdapter();

您正在调用 class 中不存在的空构造函数！所以这当然会告诉你错误

2- 即使这个构造函数（空构造函数）存在，你的代码仍然是错误的，因为在 onStop 中你调用了 terminate() class 的新对象，而不是您在 onCreate 中使用的对象（您将其命名为 adapter）。

因此，作为此解决方案，使 adapter 对象成为所有 Activity 方法的全局变量，如下所示：

private WordAdapter adapter;

和在onCreate和onStop

中使用