Java 为什么Todo应用程序不显示添加的任务？_Java_Android_Sqlite

Java 为什么Todo应用程序不显示添加的任务？

java android sqlite

Java 为什么Todo应用程序不显示添加的任务？,java,android,sqlite,Java,Android,Sqlite,Todo应用程序不显示添加的任务…就像不刷新添加的任务一样当我再次关闭并打开应用程序时，它会显示。我是初学者，所以我猜不出问题所在这里是MainActivity.java package com.ashtiv.dooo; import androidx.appcompat.app.AlertDialog; import androidx.appcompat.app.AppCompatActivity; import android.content.ContentValues; import

Todo应用程序不显示添加的任务…就像不刷新添加的任务一样当我再次关闭并打开应用程序时，它会显示。我是初学者，所以我猜不出问题所在

这里是MainActivity.java

package com.ashtiv.dooo;

import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;

import android.content.ContentValues;
import android.content.DialogInterface;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;

import com.ashtiv.dooo.db.TaskContract;
import com.ashtiv.dooo.db.TaskDbHelper;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";
    private TaskDbHelper mHelper;
    private ListView mTaskListView;
    private ArrayAdapter<String> mAdapter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mHelper = new TaskDbHelper(this);
        mTaskListView = (ListView) findViewById(R.id.list_todo);

        updateUI();
    }
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main_menu, menu);
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.action_add_task:
                final EditText taskEditText = new EditText(this);
                AlertDialog dialog = new AlertDialog.Builder(this)
                        .setTitle("Add a new task")
                        .setMessage("What do you want to do next?")
                        .setView(taskEditText)
                        .setPositiveButton("Add", new DialogInterface.OnClickListener() {


                            @Override
                            public void onClick(DialogInterface dialog, int which) {
                                String task = String.valueOf(taskEditText.getText());
                                
                                SQLiteDatabase db = mHelper.getWritableDatabase();
                                ContentValues values = new ContentValues();
                                values.put(TaskContract.TaskEntry.COL_TASK_TITLE, task);
                                db.insertWithOnConflict(TaskContract.TaskEntry.TABLE,
                                        null,
                                        values,
                                        SQLiteDatabase.CONFLICT_REPLACE);
                                db.close();
                            }
                        })
                        .setNegativeButton("Cancel", null)
                        .create();
                dialog.show();
                return true;

            default:
                return super.onOptionsItemSelected(item);
        }
    }
    public void deleteTask(View view) {
        View parent = (View) view.getParent();
        TextView taskTextView = (TextView) parent.findViewById(R.id.task_title);
        String task = String.valueOf(taskTextView.getText());
        SQLiteDatabase db = mHelper.getWritableDatabase();
        db.delete(TaskContract.TaskEntry.TABLE,
                TaskContract.TaskEntry.COL_TASK_TITLE + " = ?",
                new String[]{task});
        db.close();
        updateUI();
    }
    private void updateUI() {
        ArrayList<String> taskList = new ArrayList<>();
        SQLiteDatabase db = mHelper.getReadableDatabase();
        Cursor cursor = db.query(TaskContract.TaskEntry.TABLE,
                new String[]{TaskContract.TaskEntry._ID, TaskContract.TaskEntry.COL_TASK_TITLE},
                null, null, null, null, null);
        while (cursor.moveToNext()) {
            int idx = cursor.getColumnIndex(TaskContract.TaskEntry.COL_TASK_TITLE);
            taskList.add(cursor.getString(idx));
        }

        if (mAdapter == null) {
            mAdapter = new ArrayAdapter<>(this,
                    R.layout.item_todo,
                    R.id.task_title,
                    taskList);
            mTaskListView.setAdapter(mAdapter);
        } else {
            mAdapter.clear();
            mAdapter.addAll(taskList);
            mAdapter.notifyDataSetChanged();
        }

        cursor.close();
        db.close();
    }
}

下面是TaskDbHelper.java

package com.ashtiv.dooo.db;

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

public class TaskDbHelper extends SQLiteOpenHelper {

    public TaskDbHelper(Context context) {
        super(context, TaskContract.DB_NAME, null, TaskContract.DB_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String createTable = "CREATE TABLE " + TaskContract.TaskEntry.TABLE + " ( " +
                TaskContract.TaskEntry._ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
                TaskContract.TaskEntry.COL_TASK_TITLE + " TEXT NOT NULL);";

        db.execSQL(createTable);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + TaskContract.TaskEntry.TABLE);
        onCreate(db);
    }
}

下面是Activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:tools="http://schemas.android.com/tools"
    tools:context="com.ashtiv.dooo.MainActivity">

    <ListView
        android:id="@+id/list_todo"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</RelativeLayout>

这里是item_todo.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_gravity="center_vertical">

    <TextView
        android:id="@+id/task_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:text="Hello"
        android:textSize="20sp" />                                      

    <Button
        android:id="@+id/task_delete"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentEnd="true"
        android:layout_alignParentRight="true"
        android:text="Done"
        android:onClick="deleteTask"/>

</RelativeLayout>

您看到的问题是因为函数

updateUI（）

仅在创建活动时才会被调用。您必须设计一种方法，每次更新表时都会调用

updateUI（）

无论何时添加或删除某些任务，都可以尝试调用

updateUI（）

。例如：

@Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.action_add_task:
                final EditText taskEditText = new EditText(this);
                AlertDialog dialog = new AlertDialog.Builder(this)
                        .setTitle("Add a new task")
                        .setMessage("What do you want to do next?")
                        .setView(taskEditText)
                        .setPositiveButton("Add", new DialogInterface.OnClickListener() {


                            @Override
                            public void onClick(DialogInterface dialog, int which) {
                                String task = String.valueOf(taskEditText.getText());
                                
                                SQLiteDatabase db = mHelper.getWritableDatabase();
                                ContentValues values = new ContentValues();
                                values.put(TaskContract.TaskEntry.COL_TASK_TITLE, task);
                                db.insertWithOnConflict(TaskContract.TaskEntry.TABLE,
                                        null,
                                        values,
                                        SQLiteDatabase.CONFLICT_REPLACE);
                                db.close();
                           //NEW LINE
                            updateUI();
                            }
                        })
                        .setNegativeButton("Cancel", null)
                        .create();
                dialog.show();
                return true;

            default:
                return super.onOptionsItemSelected(item);
        }
    }

问题是您在添加新Todo后没有更新UI。要解决此问题，请按如下方式修改代码

编辑您的onOptions ItemSelected以

 @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.action_add_task:
                addTodo();
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }

并添加此函数

private void addTodo() {
    final EditText taskEditText = new EditText(this);
    AlertDialog dialog = new AlertDialog.Builder(this)
        .setTitle("Add a new task")
        .setMessage("What do you want to do next?")
        .setView(taskEditText)
        .setPositiveButton("Add", new DialogInterface.OnClickListener() {
                @Override
                    public void onClick(DialogInterface dialog, int which) {
                        String task = String.valueOf(taskEditText.getText());
                        
                        SQLiteDatabase db = mHelper.getWritableDatabase();
                        ContentValues values = new ContentValues();
                        values.put(TaskContract.TaskEntry.COL_TASK_TITLE, task);
                        db.insertWithOnConflict(TaskContract.TaskEntry.TABLE,
                                null,
                                values,
                                SQLiteDatabase.CONFLICT_REPLACE);
                        db.close();
                    }
                })
                .setNegativeButton("Cancel", null)
                .create();
        dialog.show();
        updateUI();
}

private void addTodo() {
    final EditText taskEditText = new EditText(this);
    AlertDialog dialog = new AlertDialog.Builder(this)
        .setTitle("Add a new task")
        .setMessage("What do you want to do next?")
        .setView(taskEditText)
        .setPositiveButton("Add", new DialogInterface.OnClickListener() {
                @Override
                    public void onClick(DialogInterface dialog, int which) {
                        String task = String.valueOf(taskEditText.getText());
                        
                        SQLiteDatabase db = mHelper.getWritableDatabase();
                        ContentValues values = new ContentValues();
                        values.put(TaskContract.TaskEntry.COL_TASK_TITLE, task);
                        db.insertWithOnConflict(TaskContract.TaskEntry.TABLE,
                                null,
                                values,
                                SQLiteDatabase.CONFLICT_REPLACE);
                        db.close();
                    }
                })
                .setNegativeButton("Cancel", null)
                .create();
        dialog.show();
        updateUI();
}