java.lang.InstantiationException：类COM.E没有无参数的构造

Question

我收到此错误

java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.e.www.i/com.e.www.i.Search}: java.lang.InstantiationException: class com.e.www.i.Search has no zero argument constructor 

这是下面的类：

public class Search extends Activity { 
    private RecyclerView mRecyclerView; 
    private RecyclerView.Adapter mAdapter; 

    private RecyclerView mRecyclerView1; 
    private RecyclerView.Adapter mAdapter1; 
    Context mContext; 

    public Search(Context context) { 

     mContext = context; // I guess the error is here, but I need to define context for below MyAdapter 
    } 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_recycler_view); 

     mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view); 
     mRecyclerView.setHasFixedSize(true); 
     mRecyclerView.setLayoutManager(
       new LinearLayoutManager(this,LinearLayoutManager.HORIZONTAL, false)); 
     mAdapter = new MyAdapter(getDataSet(),mContext); 
     mRecyclerView.setAdapter(mAdapter); 

     } 

private ArrayList<String> getDataSet() { 
     ArrayList results = new ArrayList<DataObject>(); 
     for (int index = 0; index < 5; index++) { 
      String obj = new String("User " + index); 
      results.add(index, obj); 
     } 
     return results; 
    } 

Answer 1

您需要定义一个没有-args构造，就像错误说：

public Search() { 
    // No args constructor 
} 

的context你需要的适配器是Activity本身，你不需要通过构造函数来获取它。只要使用this，因为你已经在一个活动的背景下：

mAdapter = new MyAdapter(getDataSet(), this); 

然后你就可以丢弃您的自定义活动中定义的重载构造函数。

Answer 2

删除Search(..) constructor，只是通过conetext到adapter像

mAdapter = new MyAdapter(getDataSet(),Search.this); 

因为你已经在Search Activity

Answer 3

在搜索时，您所创建的构造

public Search(Context context) { 
    mContext = context; 
} 

现在，既然你有用户定义的构造函数，你的编译器不提供任何默认的构造函数，所以你需要定义ap你自己也没有参数的构造函数。

public Search() { 
    // Constructor body 
}