Question

listContent.setOnItemClickListener(new AdapterView.OnItemClickListener()
    {

        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

            for(int i=0;i<showLists.size();i++){
              //
                TextView v=(TextView)listContent.getChildAt(i).findViewById(R.id.txtDes);
                v.setTextColor(Color.BLACK);

            }

            TextView v=(TextView)listContent.getChildAt(position).findViewById(R.id.txtDes);
            v.setTextColor(Color.RED);
            Toast.makeText(context,"POS "+showLists.get(position).getDes(),Toast.LENGTH_SHORT).show();

        }
    });

我一直是listview的get position项的问题。当我点击listview上的另一个项目（我的列表视图中有30个项目）显示错误时，Android刚刚在devide的creen中显示了大约12行。这是错误： ＆＃34;尝试调用虚拟方法＆＃39; android.view.View android.view.View.findViewById（int）＆＃39;在null对象引用＆＃34; 。感谢您的阅读。

Answer 1

你的问题确实是关于Null Pointer Exception，但更难确定为什么会发生这种情况。问题可以在这里找到：

for(int i=0;i<showLists.size();i++){ <-- this line actually causes the crash
//
    the crash is in the next line, at the findViewById
    TextView v=(TextView)listContent.getChildAt(i).findViewById(R.id.txtDes); 
    v.setTextColor(Color.BLACK);
}

由于recycling机制，您的for上限错误，并且由于此机制，您的列表视图永远不会具有相同的行数需要显示的数据量（阅读有关回收的内容以了解这一点）。鉴于此事实，我们确信列表视图（listContent.getChildCount()）中的观看次数将小于showLists.size()，从而使调用listContent.getChildAt(i)返回NULL当索引等于创建崩溃的listContent.getChildCount()时的值。

现在您可能想用showLists.size()更改listContent.getChildCount()并看到应用程序不再崩溃，但是如果您单击一行，那么当您滚动时其他行也会被着色清单（再循环再次成为问题）。要真正解决问题，您应该保存所选行的索引并调用notifyDatasetChanged，因此在适配器中调用getView时，只需检查当前位置以显示所选位置。如果相等，则将文本颜色更改为红色，否则更改为黑色。下面，您将找到示例的某些部分：

int currentPosition = -1;

// Just a basic adapter. The getView method is the key here
final ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1) {
        @NonNull
        @Override
        public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
            View view = super.getView(position, convertView, parent);
            if (position == currentPosition) {
                ((TextView) view).setTextColor(Color.RED);
            } else {
                ((TextView) view).setTextColor(Color.BLACK);
            }
            return  view;
        }
    };

// and here is the onItemClick
listView.setOnItemClickListener(new AdapterView.OnItemClickListener()
    {

        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            currentPosition = position;
            adapter.notifyDataSetChanged();
        }
    });

Answer 2

listContent.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            for (int i = 0; i < showLists.size(); i++) {

                TextView v = (TextView) view.findViewById(R.id.txtDes);
                v.setTextColor(Color.BLACK);

            }

            TextView v = (TextView) view.findViewById(R.id.txtDes);
            v.setTextColor(Color.RED);
            Toast.makeText(context, "POS " + showLists.get(position).getDes(), Toast.LENGTH_SHORT).show();

        }
    });

Answer 3

public View getView(int position, View convertView, ViewGroup parent)
{
    LayoutInflater inflater= (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View viewRow=convertView;
    if(viewRow==null){
        viewRow=inflater.inflate(layout,parent,false);
        viewHolder viewHolder=new viewHolder();
        viewHolder.imgIcon    = (ImageView) viewRow.findViewById(R.id.imgIcon);
        viewHolder.txtDes     = (TextView) viewRow.findViewById(R.id.txtDes);

        viewRow.setTag(viewHolder);
    }

    viewHolder  holder= (viewHolder) viewRow.getTag();
    holder.imgIcon.setImageResource(listMoiNhat.get(position).getIcon());
    holder.txtDes.setText(listMoiNhat.get(position).getDes());
    if(position==currentpos){
        holder.txtDes.setTextColor(Color.RED);
    }
    else {
        holder.txtDes.setTextColor(Color.RED);

    }
    return viewRow;
}

//这里是创建customListMoiNhat对象 final customListMoiNhat customListMoiNhat = new customListMoiNhat（context，R.layout.moinhat_customlistview，showLists，currentpos）; customListMoiNhat.notifyDataSetChanged（）; listContent.setAdapter（customListMoiNhat）;

    listContent.setOnItemClickListener(new AdapterView.OnItemClickListener()
    {

        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {



            currentpos=position;
            customListMoiNhat.notifyDataSetChanged();


        }
    });

获取列表视图错误的位置项

3 个答案: