java - 错误: incompatible types: MainFragment cannot be converted to Activity

Question

Java 类“MainFragment”

package com.example.licenta23;

import android.Manifest;
import android.app.AppComponentFactory;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.AutoCompleteTextView;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.core.app.ActivityCompat;
import androidx.fragment.app.Fragment;

import java.util.ArrayList;
import java.util.List;

public class MainFragment extends Fragment {

EditText actv1, edtModel, actv2, actv3, actv4, edtFabricatie, edtPret;
Button btnChoose, btnAdd, btnList;
ImageView imageView3;

final int REQUEST_CODE_GALLERY = 999;

public static SQLiteHelper sqLiteHelper;

private static final String[] CAROSERIE = new String[] {
        "Cabrio", "Berlina", "Coupe", "Pick-up", "Hatchback", "Break", "Off-road", "Minibus", "Monovolum", "SUV"
};

private static final String[] COMBUSTIBIL = new String[] {
        "Benzina", "Diesel", "GPL", "Electric", "Hibrid"
};

private static final String[] CULOARE = new String[] {
        "Alb", "Negru", "Gri", "Argintiu", "Albastru", "Rosu", "Verde", "Auriu", "Galben", "Portocaliu", "Maro", "Bej", "Alta culoare"
};


private List<MarcaItem> marcaList;


@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_main, container, false);


    fillMarcaList();


    AutoCompleteTextView editText = view.findViewById(R.id.actv1);
    AutoCompleteMarcaAdapter adapter = new AutoCompleteMarcaAdapter(getActivity(), marcaList);
    editText.setAdapter(adapter);

    AutoCompleteTextView editText2 = view.findViewById(R.id.actv2);
    ArrayAdapter<String> adapter2 = new ArrayAdapter<String>(getActivity(),
            android.R.layout.simple_list_item_1, CAROSERIE);
    editText2.setAdapter(adapter2);

    AutoCompleteTextView editText3 = view.findViewById(R.id.actv3);
    ArrayAdapter<String> adapter3 = new ArrayAdapter<String>(getActivity(),
            android.R.layout.simple_list_item_1, COMBUSTIBIL);
    editText3.setAdapter(adapter3);

    AutoCompleteTextView editText4 = view.findViewById(R.id.actv4);
    ArrayAdapter<String> adapter4 = new ArrayAdapter<String>(getActivity(),
            android.R.layout.simple_list_item_1, CULOARE);
    editText4.setAdapter(adapter4);



    return view;
}

private void fillMarcaList() {
    marcaList = new ArrayList<>();
    marcaList.add(new MarcaItem("Alfa Romeo", R.drawable.alfa_romeo));
    marcaList.add(new MarcaItem("Audi", R.drawable.audi));
    marcaList.add(new MarcaItem("Bmw", R.drawable.bmw));
    marcaList.add(new MarcaItem("Chevrolet", R.drawable.chevrole));
    marcaList.add(new MarcaItem("Citroen", R.drawable.citroen));
    marcaList.add(new MarcaItem("Dacia", R.drawable.dacia));
    marcaList.add(new MarcaItem("Dodge", R.drawable.dodge));
    marcaList.add(new MarcaItem("Fiat", R.drawable.fiat));
    marcaList.add(new MarcaItem("Ford", R.drawable.ford));
    marcaList.add(new MarcaItem("Honda", R.drawable.honda));
    marcaList.add(new MarcaItem("Hyundai", R.drawable.hyundai));
    marcaList.add(new MarcaItem("Jaguar", R.drawable.jaguar));
    marcaList.add(new MarcaItem("Jeep", R.drawable.jeep));
    marcaList.add(new MarcaItem("Kia", R.drawable.kia));
    marcaList.add(new MarcaItem("Land Rover", R.drawable.landrover));
    marcaList.add(new MarcaItem("Lexus", R.drawable.lexus));
    marcaList.add(new MarcaItem("Mazda", R.drawable.mazda));
    marcaList.add(new MarcaItem("Mercedes-Benz", R.drawable.mercedes));
    marcaList.add(new MarcaItem("Mini Cooper", R.drawable.minicooper));
    marcaList.add(new MarcaItem("Mitsubishi", R.drawable.mitsubishi));
    marcaList.add(new MarcaItem("Nissan", R.drawable.nissan));
    marcaList.add(new MarcaItem("Opel", R.drawable.opel));
    marcaList.add(new MarcaItem("Peugeot", R.drawable.peugeot));
    marcaList.add(new MarcaItem("Pontiac", R.drawable.pontiac));
    marcaList.add(new MarcaItem("Porche", R.drawable.porche));
    marcaList.add(new MarcaItem("Renault", R.drawable.renault));
    marcaList.add(new MarcaItem("Rover", R.drawable.rover));
    marcaList.add(new MarcaItem("Seat", R.drawable.seat));
    marcaList.add(new MarcaItem("Skoda", R.drawable.skoda));
    marcaList.add(new MarcaItem("Smart", R.drawable.smart));
    marcaList.add(new MarcaItem("Subaru", R.drawable.subaru));
    marcaList.add(new MarcaItem("Suzuki", R.drawable.suzuki));
    marcaList.add(new MarcaItem("Toyota", R.drawable.toyota));
    marcaList.add(new MarcaItem("Voltwagen", R.drawable.voltwagen));
    marcaList.add(new MarcaItem("Volvo", R.drawable.volvo));

    init();

    sqLiteHelper = new SQLiteHelper(this, "CarDB.sqlite", null, 1);

    sqLiteHelper.queryData("CREATE TABLE IF NOT EXISTS CAR (Id INTEGER PRIMARY KEY AUTOINCREMENT, 
    alegemarca VARCHAR, model VARCHAR, caroserie VARCHAR, combustibil VARCHAR, culoare VARCHAR, 
    fabricatie VARCHAR, pret VARCHAR image BLOG)");

    btnChoose.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            ActivityCompat.requestPermissions(
                    MainFragment.this,
                    new String[] {Manifest.permission.READ_EXTERNAL_STORAGE},
                    REQUEST_CODE_GALLERY
            );

        }
    });

}

@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
    super.onRequestPermissionsResult(requestCode, permissions, grantResults);
}

private void init(){
    actv1 = (EditText) getView().findViewById(R.id.actv1);
    edtModel = (EditText) getView().findViewById(R.id.edtModel);
    actv2 = (EditText) getView().findViewById(R.id.actv2);
    actv3 = (EditText) getView().findViewById(R.id.actv3);
    actv4 = (EditText) getView().findViewById(R.id.actv4);
    edtFabricatie = (EditText) getView().findViewById(R.id.edtFabricatie);
    edtPret = (EditText) getView().findViewById(R.id.edtPret);
    btnChoose = (Button) getView().findViewById(R.id.btnChoose);
    btnAdd = (Button) getView().findViewById(R.id.btnAdd);
    btnList = (Button) getView().findViewById(R.id.btnList);
    imageView3 = (ImageView) getView().findViewById(R.id.imageView3);
 }

}

SQL 数据库“SQLiteHelper.java”

package com.example.licenta23;

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteStatement;

import androidx.annotation.Nullable;

public class SQLiteHelper extends SQLiteOpenHelper {

public SQLiteHelper(@Nullable MainFragment context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {
    super(context, name, factory, version);
}

public void queryData(String sql){
    SQLiteDatabase database = getWritableDatabase();
    database.execSQL(sql);
}

public void insertData(String alegemarca, String model, String caroserie, String combustibil, String culoare, String fabricatie, String pret, byte[] image) {
    SQLiteDatabase database = getWritableDatabase();
    String sql = "INSERT INTO CAR VALUES (NULL, ?, ?, ?)";

    SQLiteStatement statement = database.compileStatement(sql);
    statement.clearBindings();

    statement.bindString(1, alegemarca);
    statement.bindString(2, model);
    statement.bindString(3, caroserie);
    statement.bindString(4, combustibil);
    statement.bindString(5, culoare);
    statement.bindString(6, fabricatie);
    statement.bindString(7, pret);
    statement.bindBlob(8, image);

    statement.executeInsert();
}

public Cursor getData(String sql){
    SQLiteDatabase database = getReadableDatabase();
    return database.rawQuery(sql, null);

}

@Override
public void onCreate(SQLiteDatabase db) {

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

 }
}

而且，我的错误是:

C:\Users\tibim\AndroidStudioProjects\licenta23\app\src\main\java\com\example\licenta23\MainFragment.java:130: error: incompatible types: MainFragment cannot be converted to Activity
                    MainFragment.this,

Answer 1

首先像这样更改构造函数助手(删除 MainFragment 并设置 Context):

 public SQLiteHelper(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {
    super(context, name, factory, version);
 }

接下来在 fragment 中初始化 Activity ，如下所示:

   private AppCompatActivity activity;


    @Override
    public void onAttach(@NonNull Context context) {
       super.onAttach(context);
       if (context instanceof AppCompatActivity) {
          activity = (AppCompatActivity) context;
      }
    }

接下来更改您的帮助程序和点击监听器以获得权限:

  //...
    sqLiteHelper = new SQLiteHelper(activity, "CarDB.sqlite", null, 1);




 //...
     btnChoose.setOnClickListener(new View.OnClickListener() {
     @Override
     public void onClick(View view) {
        ActivityCompat.requestPermissions(
              //this change
                activity,
                new String[] {Manifest.permission.READ_EXTERNAL_STORAGE},
                REQUEST_CODE_GALLERY
             );

         }
    });