Question

我需要为ListView中的每一行存储隐藏的ID值。基本上是一个变量，包含代码所需的字符串值以及用户不需要查看的内容。

用户输入nameField EditText
点击saveName Button
值将保存到ViewHolder
打印

注意：请注意，每行都有String值存储。每行都有一个String值存储在ViewHolder中。这就是我想要实现的目标。

我的方法是在String类中声明一个ViewHolder变量，希望它将保留该特定行的值。但是我注意到，当适配器回收该行时，字符串值将重置为空字符串。

适配器：

@Override
public View getView(final int position, View convertView, ViewGroup parent) {

        final ViewHolder holder;

        if (convertView == null) {
            inflater = (LayoutInflater) activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = inflater.inflate(R.layout.custom_row, null);
            holder = new ViewHolder();
            holder.saveName = (Button) convertView.findViewById(R.id.saveName);
            holder.nameField = (EditText) convertView.findViewById(R.id.nameField);
            convertView.setTag(holder);
        }
        else {
            holder = (ViewHolder) convertView.getTag();
        }

        //Button That saves what the user entered in the nameField to the String variable
        holder.saveName.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                  holder.hidden_value = nameField.getText().toString();
            }
        });

        //Just to check whether the value is saved when I recycle listview when scrolling
        Log.d("test", holder.hidden_value);
        //It logs an empty string. The value from the editext was not saved! 
}

static class ViewHolder {
        EditText nameField;
        Button saveName;
        String hidden_value = "";
}

为什么值不会保存在字符串中？当我尝试记录它时，它会记录一个空字符串！我做错了什么？

Answer 1

您无法在ViewHolder中存储价值。您使用holder = (ViewHolder) convertView.getTag();获取ViewHolder。此ViewHolder是其他视图的表单标记，而不是您在此位置存储的ViewHolder。

private SparseArray<String> values = new SparseArray<>();
@Override
public View getView(final int position, View convertView, ViewGroup parent) {

        final ViewHolder holder;

        if (convertView == null) {
            inflater = (LayoutInflater) activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = inflater.inflate(R.layout.custom_row, null);
            holder = new ViewHolder();
            holder.saveName = (Button) convertView.findViewById(R.id.saveName);
            holder.nameField = (EditText) convertView.findViewById(R.id.nameField);
            convertView.setTag(holder);
        }
        else {
            holder = (ViewHolder) convertView.getTag();
        }

        //Button That saves what the user entered in the nameField to the String variable
        holder.saveName.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                  values.put(position,nameField.getText().toString());
            }
        });

        //Just to check whether the value is saved when I recycle listview when scrolling
        Log.d("test", values.get(position,"null"));
        //It logs an empty string. The value from the editext was not saved! 
}

static class ViewHolder {
        EditText nameField;
        Button saveName;
        String hidden_value = "";
}

Answer 2

问题是，ViewHolder应该包含“视图”而不是“数据”。您需要在此处更改您的实施。将值存储在要传递给适配器的数组中。这是实际保存“数据”的数组。

因此，您的自定义适配器的构造函数将是，

public CategoryListViewAdapter(Context c, ArrayList<MyData> al) {
    mContext = c;
    mArrayList = al;
    ....
}

MyData将有您的ID字段

class Mydata{
    String ID;
    ....
}

有关此主题的完整教程，请参阅this。它有你需要知道的一切。

在Android ListView适配器中存储String变量

2 个答案: