Android GridView 回收问题

Question

当我每次尝试使用回收的 gridview 时，如果 convertView != null 那么我得到一个错误，这是我的源代码。它会在 text = (TextView) convertView; 处给我一个错误在 else 语句中。我真的迷失在这里，我会停止回收 View ，但它会占用大量内存和不稳定的滚动

$ 这里是 imageadapter.java

public View getView(int position, View convertView, ViewGroup parent) {
    RelativeLayout lay;

    ImageView image;
    TextView text;
    if (convertView == null) {
        Log.d("height", "Width = " + width);

        lay = new RelativeLayout(mContext);
        image = new ImageView(mContext);
        text = new TextView(mContext);


        //text.setText("This is a test");
        text.setTextSize(14);
        text.setTextColor(Color.WHITE);
        text.setGravity(Gravity.LEFT | Gravity.TOP);
        text.setPadding(2, 2, 2, 2);
        text.setBackgroundColor(Color.parseColor("#80000000"));
        RelativeLayout.LayoutParams textLayout = new RelativeLayout.LayoutParams(
                (int) Math.round(width / 2.0),
                (int) Math.round(width / 8.3));

        textLayout.addRule(RelativeLayout.ALIGN_PARENT_BOTTOM);
        text.setLayoutParams(textLayout);

        MarginLayoutParams textMarginFix = (ViewGroup.MarginLayoutParams) text
                .getLayoutParams();
        textMarginFix.setMargins(0, 0, 0, (int) Math.round(width / 45.0));
        text.setLayoutParams(textMarginFix);

        image.setLayoutParams(new LayoutParams((int) Math
                .round(width / 2.0), (int) Math.round(width /              2.0)));

        image.setScaleType(ImageView.ScaleType.CENTER_CROP);
        //image.setImageResource(mThumbIds[position]);

        lay.setLayoutParams(new GridView.LayoutParams((int) Math
                .round(width / 2.0), (int) Math.round(width / 2.0)));
        lay.setBackgroundResource(R.drawable.shadowimage);
        lay.setPadding(5, 5, 15, 15);
        //lay.setId(mThumbIds[position]);

        //lay.addView(image);
        //lay.addView(text);

    } 
    else
    {
        text = (TextView) convertView;
        image = (ImageView) convertView;
        lay = (RelativeLayout) convertView;
    }

    image.setImageResource(mThumbIds[position]);
    text.setText("This is a test");

    lay.addView(image);
    lay.addView(text);

     return lay;

}
$here is where i call the imageadapter from another class

    @Override
public Object instantiateItem(View container, int position) {
   View contentView;        
   switch (position) {
    case 0:
        LayoutInflater mInflater = LayoutInflater.from(mContext);
        View contentView = mInflater.inflate(R.layout.image_grid_view,   null);
        Display display = mContext.getWindowManager().getDefaultDisplay();
        final int width = display.getWidth();
        int height = display.getHeight();
        float scale = mContext.getResources().getDisplayMetrics().density;
        GridView gridview = (GridView) contentView.findViewById(R.id.gridview);
        gridview.setAdapter(new ImageAdapter(mContext, width, height, scale));
        gridview.setFocusable(true);
        gridview.requestFocus();
        gridview.setOnItemClickListener(itemClickListener);

        ((ViewPager) container).addView(contentView, 0);
        break;
...return contentView

Answer 1

convertView 是完全代表您的 GridView 中的一个 项目的 View 。如果那是一个 TextView，它将是一个 TextView，如果它是一个完整的布局，您将收到整个布局等等。

那么您如何知道和定义什么是“表示一个项目的 View ”？很简单，它是您在 convertView == null 然后从 getView return 时创建的任何内容。

只是您收到了一件用过的元素，您只是对其进行修改以将其更新为适当的内容。因此，您应该利用类型转换来以您想要的格式获取您收到的此 View。

像下面这样的代码会让你得到你想要的，而不需要重做你不需要做的事情(也就是你不需要从 convertView 重新添加子 Views >，只有一个新 View ):

public View getView(int position, View convertView, ViewGroup parent) {
    RelativeLayout lay;
    ImageView image;
    TextView text;

    if (convertView == null) {
        // Setup your 'item view'
        lay = new RelativeLayout(mContext);
        image = new ImageView(mContext);
        text = new TextView(mContext);

        // Do all your customizing stuff (aka size, color, format, padding layout params)

        lay.addView(image, 0);
        lay.addView(text, 1);
    } else {
        lay = (RelativeLayout) convertView;
        image = (ImageView) lay.getChildAt(0);
        text = (TextView) lay.getChildAt(1);
    }

    // Set content for your image and text

    return lay;
}