Question

我创建测试空片段。它没有任何元素，返回 null 。然后我运行应用程序。在最初的方向，一切都很好。

static FragmentTransaction fragment_trans;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    TableClassFragment tableFragment = new TableClassFragment(12);

    fragment_trans = getFragmentManager().beginTransaction();
    fragment_trans.add(R.id.tableFragment, tableFragment);
    fragment_trans.commit();

}

static class TableClassFragment extends Fragment {

    int table_size;
    String[] sequence_letters_in_table = {};

    public TableClassFragment(int _size){
        table_size = _size;
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)     {
        return null;
    }
}

当我改变方向时 - 得到错误

FATAL EXCEPTION: main
Process: bairro.lettersgenerator, PID: 2885
java.lang.RuntimeException: Unable to start activity ComponentInfo{bairro.lettersgenerator/bairro.lettersgenerator.MainActivity}: 
android.app.Fragment$InstantiationException: Unable to instantiate fragment bairro.lettersgenerator.MainActivity$TableClassFragment: make sure class name exists, is public, 
and has an empty constructor that is public
Caused by: java.lang.InstantiationException: can't instantiate class bairro.lettersgenerator.MainActivity$TableClassFragment; 
no empty constructor

请帮忙

Answer 1

InstantiationException：[...] TableClassFragment; 没有空构造函数

你TableClassFragment应该有＃34;空构造函数＆＃34;：

static class TableClassFragment extends Fragment {

    int table_size;
    String[] sequence_letters_in_table = {};

    public TableClassFragment() {
        // ...
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)     {
        return null;
    }
}

使用Fragment.setArguments()将参数传递给它。

Answer 2

您的片段中需要一个空的构造函数，这就是您收到此错误的原因。

像：

public TableClassFragment(){
}

Answer 3

将table_size传递给TableClassFragment作为Bundle

TableClassFragment tableFragment = new TableClassFragment();
Bundle bunble =new Bundle();
bunble.putInt(TableClassFragment.ARG_TABLESIZE , 12);
tableFragment setArguments(bundle);

更改TableClassFragment

public class FaceScanExampleFragment extends Fragment{
final static String ARG_TABLESIZE = "table_size";
 int table_size;


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
    Bundle savedInstanceState) {
    ......
    if (savedInstanceState != null) {
        table_size = savedInstanceState.getInt(ARG_TABLESIZE);
    }
   ......

}

@Override
public void onStart() {
    super.onStart();


    Bundle args = getArguments();
    if (args != null) {
        // Set article based on argument passed in
        updateArticleView(args.getInt(ARG_TABLESIZE));
    } else
    }
}

public void updateArticleView(int position) {

    table_size = position;
}

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);

    // Save the current article selection in case we need to recreate the fragment
    outState.putInt(ARG_TABLESIZE, table_size);
}

Answer 4

试试这个：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

View rootView = inflater.inflate(R.layout.your_layout, container, false);
Toast.makeText(getActivity(), "FirstFragment.onCreateView()",
                Toast.LENGTH_LONG).show();
return rootView;
    }
}

用班级改变方向错误

4 个答案: