【发布时间】：2020-08-18 08:47:37
【问题描述】：
我有一个 Android Studio 程序（在 Java 中）从用户那里收集数据，然后允许他们 a) 通过按添加按钮将该数据输入到表中，或 b) 从表中删除该信息（如果它已经在那里）按删除按钮。这并不令人惊奇，但它是练习并且有效。问题是我想让这些操作发生在后台线程而不是 UI 线程中。
我似乎不知道该怎么做。我发现的所有提议的解决方案要么不适用于我的情况，要么我尝试实施它们但失败了（或者它们不起作用；我无法分辨出我目前的技能水平的区别）。帮助将不胜感激。相关文件如下。 （请注意，我在这里从代码中删除了包名，因为它们中有我的真实姓名，但它们在实际文件中）。
DataEntryForm.java（这是我的添加和删除按钮以及它们的 onClick 方法所在的位置）
import android.app.Activity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.Spinner;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
public class DataEntryForm extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_data_entry_form);
final Spinner spinner = findViewById(R.id.categorySelect);
ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this,
R.array.categories_Array, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner.setAdapter(adapter);
final DBAdapter db = new DBAdapter(this);
db.open();
final EditText recipeNameInput = findViewById(R.id.recipeNameInput);
final Spinner categorySelect = findViewById(R.id.categorySelect);
final EditText ingredientsInput = findViewById(R.id.ingredientsInput);
final EditText instructionsInput = findViewById(R.id.instructionsInput);
Button addBtn = findViewById(R.id.addBtn);
Button deleteBtn = findViewById(R.id.deleteBtn);
addBtn.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View v) {
new BackgroundThread().execute();
String editRecipeName = recipeNameInput.getText().toString();
String chooseCategory = categorySelect.getSelectedItem().toString();
String editIngredients = ingredientsInput.getText().toString();
String editInstructions = instructionsInput.getText().toString();
db.insertRecipeChoice(editRecipeName, chooseCategory, editIngredients, editInstructions);
Toast.makeText(DataEntryForm.this, "Recipe added!", Toast.LENGTH_LONG).show();
}
});
deleteBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
new BackgroundThread().execute();
if (db.deleteChoice(1))
Toast.makeText(DataEntryForm.this, "Recipe deleted!", Toast.LENGTH_LONG).show();
else
Toast.makeText(DataEntryForm.this, "Recipe deletion failed!",
Toast.LENGTH_LONG).show();
}
}
);
}
}
请注意，在我之前的一次尝试中，其中有一个“new BackgroundThread.execute()”行。我暂时把它留了下来，以防万一事实证明这是正确的想法。我不想让它溜走。
DBAdapter.java
import android.content.ContentValues;
import android.content.Context;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;
public class DBAdapter extends AppCompatActivity{
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.adapter_db);
}
static final String KEY_ROWID = "_id";
static final String KEY_RECIPENAME = "RecipeName";
static final String KEY_CATEGORY = "Category";
static final String KEY_INGREDIENTS = "Ingredients";
static final String KEY_INSTRUCTIONS = "Instructions";
static final String TAG = "DBAdapter";
static final String DATABASE_NAME = "MyDB";
static final String DATABASE_TABLE = "MyChoices";
static final int DATABASE_VERSION = 1;
static final String DATABASE_CREATE = "create table MyChoices (_id integer primary key autoincrement, " + "RecipeName text not null, category text not null, ingredients text not null, instructions text not null);";
final Context context;
DatabaseHelper DBHelper;
SQLiteDatabase db;
public DBAdapter(Context ctx) {
this.context = ctx;
DBHelper = new DatabaseHelper(context);
}
private static class DatabaseHelper extends SQLiteOpenHelper {
DatabaseHelper(Context context)
{
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
try {
db.execSQL(DATABASE_CREATE);
} catch (SQLException e) {
e.printStackTrace();
}
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Log.w(TAG, "Upgrading database from version " + oldVersion + " to " + newVersion + ", which will destroy all old data");
db.execSQL("DROP TABLE IF EXISTS MyChoices");
onCreate(db);
}
}
//---opens the database----
public DBAdapter open() throws SQLException {
db = DBHelper.getWritableDatabase();
return this;
}
//---closes the database----
public void close() {
DBHelper.close();
}
//---insert a recipe choice into the database---
public long insertRecipeChoice(String recipeName, String category, String ingredients, String instructions) {
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_RECIPENAME, recipeName);
initialValues.put(KEY_CATEGORY, category);
initialValues.put(KEY_INGREDIENTS, ingredients);
initialValues.put(KEY_INSTRUCTIONS, instructions);
return db.insert(DATABASE_TABLE, null, initialValues);
}
//---deletes a particular recipe choice---
public boolean deleteChoice(long rowId) {
return db.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0;
}
}
BackgroundThread.java 这大部分是空的，因为我只是想弄清楚我是否需要这个单独的类，如果需要，我应该在这里放什么。 p>
import android.content.Context;
import android.os.AsyncTask;
public class BackgroundThread extends AsyncTask<Void, Void, Void> {
@Override
protected Void doInBackground(Void... voids) {
return null;
}
@Override
protected void onPostExecute(Void aVoid) {
super.onPostExecute(aVoid);
}
}
如果我需要包含其他任何内容来获得此问题的答案，请告诉我，但我认为这些是相关文件。其他一切都不会触及或影响表格或数据。
【问题讨论】：
标签： java android database android-asynctask onclick