android - 如何在 fragment 中使用切换按钮

Question

这是我的类代码，我想在其中访问切换按钮但出现空指针异常。我使用 ViewHolder 类从布局获取 View 并在此处访问它们。但无法找到错误，为什么我在 < br/> holder.stateOnOff.setText();行

 public class ColorSchemeFragment extends Fragment {

public  class ViewHolder {
    public  ToggleButton toggleButton;
    public TextView stateOnOff;
}
ViewHolder holder = new ViewHolder();

@Override
public View onCreateView(LayoutInflater inflater, 
 ViewGroup container,Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.colorscheme, container, false);
    holder.toggleButton = ((ToggleButton) container.findViewById(R.id.toggle));
    holder.stateOnOff=(TextView)container.findViewById(R.id.tvstate);
    holder.stateOnOff.setText("OFF");
    holder.toggleButton.setOnCheckedChangeListener(new OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(CompoundButton buttonView,boolean isChecked) {
            if(isChecked){
                holder.stateOnOff.setText("On");
            }else{
                holder.stateOnOff.setText("Off");
            }
                }
            });
        return view;
        }
       }

Answer 1

无需使用 ViewHolder。它们用于通过 ListView 或其他可 ScrollView 回收 View 。

此外，container 对象包含父布局，而不是您正在膨胀的布局。因此它不包含您正在查找的 View 并返回 null。

public class ColorSchemeFragment extends Fragment {

public ToggleButton toggleButton;
public TextView stateOnOff;

@Override
public View onCreateView(LayoutInflater inflater, 
 ViewGroup container,Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.colorscheme, container, false);
    toggleButton = (ToggleButton) view.findViewById(R.id.toggle);
    stateOnOff=(TextView) view.findViewById(R.id.tvstate);
    stateOnOff.setText("OFF");
    toggleButton.setOnCheckedChangeListener(new OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(CompoundButton buttonView,boolean isChecked) {
            if(isChecked){
                stateOnOff.setText("On");
            }else{
                stateOnOff.setText("Off");
            }
                }
            });
        return view;
        }
     }