如何访问 GridView / 数组中的特定项目（在 Android 应用中）

Question

在 Android Studio 中编写一个 Android 应用时，我有一个 GridView 来显示一组图像/文本，但我无法确定如何访问列表中的特定项目。

如果我点击一个项目，我可以对它做一些事情（在下面的代码中，我更改了显示的图像），但我不知道如何以编程方式访问特定项目（例如更改显示的图像） .

最初我使用了一个示例中的 ImageAdapter，但后来我发现如果我将其更改为使用 TextView，我可以为每个文本以及一个图像分配文本，并且它可以很好地与 Talkback（Android 屏幕阅读器）一起使用.

我最初也将 OnTouchListener 添加到活动中，但我认为我现在不需要它，因为我只需要在适配器中实现它。

最后，我对究竟需要在这里访问什么感到有点困惑——我是想从​​ GridView 中取出项目，还是从 ImageAdapter 中取出项目？我认为 GridView 设置布局并定义在集合中放置每个项目的位置，而 ImageAdapter 是用于定义集合中每个项目的属性的项目数组的容器，对吗？

亲切的问候

昆汀。

public class multitap extends Activity implements View.OnTouchListener {

    private GridView myGridView;
    public int numRows;
    public int numCols;
    public int currentChoice;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_multitap);
        if (savedInstanceState == null) {
            Bundle extras = getIntent().getExtras();
            if (extras == null) {
                numRows = 1;
                numCols = 1;
            } else {
                numRows = extras.getInt("NUMBER_OF_GAME_ROWS");
                numCols = extras.getInt("NUMBER_OF_GAME_COLS");
            }
        } else {
            numRows = (int) savedInstanceState.getSerializable("NUMBER_OF_GAME_ROWS");
            numCols = (int) savedInstanceState.getSerializable("NUMBER_OF_GAME_COLS");
        }

        myGridView = (GridView)
                findViewById(R.id.myGridView);
        myGridView.setNumColumns(numCols);
        myGridView.setAdapter(new ImageAdapter(this));

        // now that everything is initialised, choose a random image tile.
        Random r = new Random();
        choice = r.nextInt(numCols*numRows);

    // This is the main thing I can't figure out - what do I need to replace "DoSomethingToFindItem" with?
    chosenItem = DoSomethingToFindItem(choice);
        // change the image of the chosen tile.
        chosenItem.setBackgroundResource(R.drawable.newImage);


    }

    @Override
    public boolean onTouch(View v, MotionEvent event) {

        // turns out I don't need this as onTouch in adapter collects touch event
        return false;

    }


    public class ImageAdapter extends BaseAdapter {
        private Context mContext;

    //not really sure what mConext is?
        public ImageAdapter(Context c) {
            mContext = c;
        }

        public int getCount() { return numCols*numRows; }

        public Object getItem(int position) {
        // Is this right? All of the examples on the net use "return null" claiming they it's not needed (for their example)
            return this;
        }

        public long getItemId(int position) {
            // I know I should return something other than position here, but don't know what?
            // again every example doesn't feel the need for this function.
            return position;
        }

        // create a new TextView for each item referenced by the Adapter
        public View getView(int position, View convertView, ViewGroup parent) {
            TextView textView;

            if (convertView == null) {  // if it's not recycled, initialize some attributes
                textView = new TextView(mContext);

            } else {
                textView = (TextView) convertView;
            }

            textView.setBackgroundResource(R.drawable.blankcell);
            textView.setText("" + (position + 1));
            textView.setTextColor(getResources().getColor(android.R.color.transparent));
            textView.setId(position);
            textView.setMaxHeight(parent.getHeight() / numRows);
            textView.setMinimumHeight(parent.getHeight() / numRows);


            textView.setOnTouchListener(new View.OnTouchListener() {
                public boolean onTouch(View v, MotionEvent event) {
                    int position;
                    position = v.getId();

                    // looking to get the first touch of any finger - this part works.
                    if ((event.getAction() == MotionEvent.ACTION_DOWN) || (event.getAction() == MotionEvent.ACTION_POINTER_DOWN)) {
                        TextView textView;
                        if (v == null) {  // if it's not recycled, initialize some attributes
                            textView = new TextView(mContext);

                        } else {
                            textView = (TextView) v;
                        }

                        // I can set a specific image by clicking on it.
                        textView.setBackgroundResource(R.drawable.clickedImage);

                        return true;
                    } else return false;
                }

                ;});
            return textView;
        }

    }
}

Answer 1

好的，通常情况下，我最初遇到了几个问题。一个是访问 GridView 中的项目，Rami 的回答（来自How to find element inside a gridview in Android? 的回答）是正确的：

// newChoice is an int set to something in the range 0...myGridView.getChildCount()

v = (TextView) myGridView.getChildAt(newChoice);
v.setBackgroundResource(themeImages[ACTIVE1]);

一开始我没有意识到的第二个问题是，我试图从视图中获取的信息中的逻辑在视图被绘制后就会起作用，但是因为这段代码设法在视图被执行之前被执行所有完成的绘图，值不是我预期的，这意味着标记为可见的项目的高度为 0 等。我发现这段代码有帮助：getWidth() and getHeight() of View returns 0

final View theParent = parent;
final TextView theText = textView;
textView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
    @Override
    public void onGlobalLayout() {
        theText.post(new Runnable() {
            public void run() {
                // Now height is ready
                theText.setLayoutParams(new GridView.LayoutParams(GridView.AUTO_FIT, (theParent.getHeight() / numRows)));
            }
        });
    }
});

感谢拉米的帮助和建议！ （我还按照您的建议将直接引用图像文件更改为使用数组）。