Java 在Android中访问ListView复选框

我正在android上制作一个待办事项列表应用程序。除了在ListView中有无法以编程方式设置的复选框外，其他一切都运行得很好。我正在使用一个SQLite数据库来存储我的任务以及它们是否被标记为已完成。当我选中复选框时，它会成功地在我的数据库中保存一个“1”。我有一个updateUI方法，可以从数据库中读取任务的文本并显示它。我创建了一个新的“updateUICheckBox”方法来处理复选框的UI更新。现在我只是想把我所有的复选框都设置为选中，但是当我调用setChecked（true）时，我得到了一个nullpointerexception

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由于要设置复选框的是ListView项，因此必须在ListView本身的适配器中设置它。并操纵数据模型以选中或取消选中复选框

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通过扩展用于填充ListView的BaseAdapter创建新类。如果要管理的自定义布局包含多个UI对象，请不要使用ArrayAdapter

尝试在列表中添加标志

public class Country {
    public String name;
    public String code;
    public String abbreviation;
    public boolean selected = false;   //--> example this flag
    public int image;
}

适配器

public class CountryCodeAdapter extends BaseAdapter {
    private Context context;
    private List<Country> countryList;


    public CountryCodeAdapter(Context context, List<Country> countryList) {
        this.context = context;
        this.countryList = countryList;
    }

    @Override
    public int getCount() {
        return countryList.size();
    }

    @Override
    public Object getItem(int position) {
        return countryList.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder viewHolder;
        if (convertView == null) {
            convertView = LayoutInflater.from(context).inflate(R.layout.adapter_country_code, parent, false);
            viewHolder = new ViewHolder(convertView);
            convertView.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) convertView.getTag();
        }

        Country country = countryList.get(position);
        viewHolder.tv_item_country_name.setText(country.getName());

        String plus = context.getResources().getString(R.string.plus);
        viewHolder.tv_item_country_code.setText(plus.concat(country.getCode()));
        int image = country.getImage();
        if (image != -1) {
            viewHolder.iv_item_country.setImageResource(image);
        }

        return convertView;
    }

    public void updateList(List<Country> countryList) {
        this.countryList = countryList;
        notifyDataSetChanged();
    }

    static class ViewHolder {
        @Bind(R.id.iv_item_country)
        ImageView iv_item_country;
        @Bind(R.id.tv_item_country_name)
        TextView tv_item_country_name;
        @Bind(R.id.tv_item_country_code)
        TextView tv_item_country_code;

        public ViewHolder(View view) {
            ButterKnife.bind(this, view);
        }
    }
}

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使用此标志在适配器内设置复选框。

我添加了一个扩展BaseAdapter的内部类（请参见上面的编辑）。我填写了getView方法。我如何在updateUICheckBox方法中利用它根据数据库值设置复选框？请检查此实现

public class CountryCodeAdapter extends BaseAdapter {
    private Context context;
    private List<Country> countryList;


    public CountryCodeAdapter(Context context, List<Country> countryList) {
        this.context = context;
        this.countryList = countryList;
    }

    @Override
    public int getCount() {
        return countryList.size();
    }

    @Override
    public Object getItem(int position) {
        return countryList.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder viewHolder;
        if (convertView == null) {
            convertView = LayoutInflater.from(context).inflate(R.layout.adapter_country_code, parent, false);
            viewHolder = new ViewHolder(convertView);
            convertView.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) convertView.getTag();
        }

        Country country = countryList.get(position);
        viewHolder.tv_item_country_name.setText(country.getName());

        String plus = context.getResources().getString(R.string.plus);
        viewHolder.tv_item_country_code.setText(plus.concat(country.getCode()));
        int image = country.getImage();
        if (image != -1) {
            viewHolder.iv_item_country.setImageResource(image);
        }

        return convertView;
    }

    public void updateList(List<Country> countryList) {
        this.countryList = countryList;
        notifyDataSetChanged();
    }

    static class ViewHolder {
        @Bind(R.id.iv_item_country)
        ImageView iv_item_country;
        @Bind(R.id.tv_item_country_name)
        TextView tv_item_country_name;
        @Bind(R.id.tv_item_country_code)
        TextView tv_item_country_code;

        public ViewHolder(View view) {
            ButterKnife.bind(this, view);
        }
    }
}

CountryCodeAdapter adapter = new CountryCodeAdapter(activity, countryList);
//eg. you may change the 1st element in countryList selected flag into true and //call updateList 
        if (adapter != null) {
            adapter.updateList(countryList);
        }