Question

我正在制作小型待办事项应用程序，但我遇到了问题这个想法是：

将数据保存到数据库中 - ＆gt;在ListView中检索它。

此刻，我的应用程序在按下“BUILD”后立即崩溃按钮，即使我认为它应该只是说“保存！” （确保将数据保存到数据库中）关于如何在ListView中显示数据的一些提示将非常受欢迎。

P.S。：这是我的第一个应用，所以不要苛刻

代码：

Mainactivity

package com.example.mrti.todo2;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.Toast;
import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {

TaskDbHelper taskDbHelper;
SQLiteDatabase SQLdb;
ArrayAdapter<String> itemsAdapter;
Context context;

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

    ListView lvItems = (ListView) findViewById(R.id.listView);
    ArrayList<String> items = new ArrayList<String>();

    itemsAdapter = new ArrayAdapter<String>(this,
            android.R.layout.simple_list_item_1, items);
    lvItems.setAdapter(itemsAdapter);


}

// ADDING YOUR FUTURE GOALS!
public void onBuildButton (View view){
    EditText dreamText = (EditText) findViewById(R.id.dreamText);
    String task = dreamText.getText().toString();

    //db
    taskDbHelper = new TaskDbHelper(context);
    SQLdb = taskDbHelper.getWritableDatabase();
    taskDbHelper.insertData(task, SQLdb);
    Toast.makeText(getBaseContext(), "Saved!", Toast.LENGTH_LONG).show();
    taskDbHelper.close();
}


}

TaskDBHelper.java

public class TaskDbHelper extends SQLiteOpenHelper {

private static final String DATABASE_NAME = "TASKS.db";
private static final int DB_VERSION = 1;
private static final String CREATE_QUERY =
                        "CREATE TABLE " +         TaskContract.newTaskInfo.TABLE_NAME + " ( " +
                        TaskContract.newTaskInfo.TASK_NAME + " TEXT NOT NULL);";


public TaskDbHelper(Context context) {
    super(context, DATABASE_NAME, null, DB_VERSION);
}

@Override
public void onCreate(SQLiteDatabase db) {
    db.execSQL(CREATE_QUERY);
    Log.e("DB Operations", "Table created...");
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    db.execSQL("DROP TABLE IF EXISTS " + TaskContract.newTaskInfo.TABLE_NAME);
    onCreate(db);
}
// For adding new data to database
public void insertData(String task, SQLiteDatabase db){
    ContentValues contentValues = new ContentValues();
    contentValues.put(TaskContract.newTaskInfo.TASK_NAME, task);
    db.insert(TaskContract.newTaskInfo.TABLE_NAME, null, contentValues);
        Log.e("DB Operations", "1 record added...");

}
}

TaskContract.java

public class TaskContract {

public static abstract class newTaskInfo{
    public static final String TASK_NAME = "task_name"; // Table field
    public static final String TABLE_NAME = "task_info"; // Name of the table
}

Answer 1

您的context变量为null且不必要。

活动是上下文，所以请改用

taskDbHelper = new TaskDbHelper(MainActivity.this);

将数据保存到数据库并在ListView中检索它

1 个答案: