对于评论功能SQLite数据库

Question

有一个与代码没有任何错误。不过，我想建立一个注释部分，其中的名称和注释将被保存在数据库中（SQLite的）。

1）它不会停留在TextView中后，我来自另一个页面回来。 2）实施例，我评论一次，和注释显示。我再次发表评论，它实际上重新显示以前的和新的评论意见。

public class BuyerHome extends AppCompatActivity {
DatabaseHelper2 myDB;
//EditText name,comment;

EditText nameIn;
EditText commentIn;
TextView viewComment;

Button postComment;



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

    nameIn = (EditText) findViewById(R.id.nameInput);
    commentIn = (EditText) findViewById(R.id.commentText);
    viewComment = (TextView) findViewById(R.id.viewCommentText);
    myDB = new DatabaseHelper2(this);



    postComment = (Button) findViewById(R.id.buttonComment);

    postComment.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            String name = nameIn.getText().toString();
            String comment = commentIn.getText().toString();

            if(nameIn.length()!=0 && commentIn.length()!=0){
                AddData(name,comment);
                nameIn.setText("");
                commentIn.setText("");
            }else{
                Toast.makeText(BuyerHome.this, "Insert fields", 
Toast.LENGTH_SHORT).show();
            }

            Cursor data = myDB.getContents();

            if(data.getCount()==0){
                Toast.makeText(BuyerHome.this, "Database empty", 
Toast.LENGTH_SHORT).show();
            }
            else{

                while(data.moveToNext()){
                    viewComment.append(data.getString(1));
                    viewComment.append(data.getString(2)+"\n");
                }
            }

            //viewComment.append("\n"+name+":"+comment);




    }
});
}
    public void AddData(String name,String comment){
    boolean insertData = myDB.insertData(name,comment);

    if(insertData==true){
        Toast.makeText(this, "Success", Toast.LENGTH_SHORT).show();
    }else{
        Toast.makeText(this, "Fail", Toast.LENGTH_SHORT).show();
    }
      }
}

1）我想在过去的意见，只要页面可以在那里。 2）我只想显示（在过去的评论顶部的最新评论），而不是过去的评论（又重新显示）与新的评论。

Answer 1

我想也许是使用了较旧评论的第二图建议。您还需要确定最新的，而不是旧的评论的一种手段。

在第二视图下面的例子是一个ListView（这将让你点击一个特定的消息，也许引用它，或许提取名）。

该示例迎合用于确定经由id列的最后发布的评论的两种方法（实际使用作为列名音符_id因为这然后允许用于可以是有利ListView的一个光标适配器）。

为了便于显示返回的onResume方法之后的评论已被重写旅馆的活动。

下面的代码： -

database helper2.Java

public class DatabaseHelper2 extends SQLiteOpenHelper {

    private final static String DBNAME = "buyerdb";
    private final static int DBVERSION = 1;

    public final static String TBL_COMMENT = "comment";
    public final static String COL_COMMENT_ID = BaseColumns._ID;
    public final static String COL_COMMENT_NAME = "name";
    public final static String COL_COMMENT_COMMENT = "comment";
    public final static String COl_COMMENT_TIMESTAMP = "timestamp";

    private String crt_tbl_comment = "CREATE TABLE IF NOT EXISTS " + TBL_COMMENT + "(" +
            COL_COMMENT_ID + " INTEGER PRIMARY KEY, " +
            COL_COMMENT_NAME + " TEXT," +
            COL_COMMENT_COMMENT + " TEXT, " +
            COl_COMMENT_TIMESTAMP + " TEXT DEFAULT CURRENT_TIMESTAMP" +
            ")";

    SQLiteDatabase mDB;

    public DatabaseHelper2(Context context) {
        super(context, DBNAME, null, DBVERSION);
        mDB = this.getWritableDatabase();
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(crt_tbl_comment);
    }

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

    }

    public long addData(String name, String comment) {
        ContentValues cv = new ContentValues();
        cv.put(COL_COMMENT_NAME,name);
        cv.put(COL_COMMENT_COMMENT,comment);
        return mDB.insert(TBL_COMMENT,null,cv);
    }

    public Cursor getLatestComment() {
        return mDB.query(TBL_COMMENT,null,null,null,null,null,COl_COMMENT_TIMESTAMP + " DESC","1");
    }

    public Cursor getAllButLatestComment() {
        String whereclause = COL_COMMENT_ID + " < (SELECT max(" +
                COL_COMMENT_ID +
                ") FROM " + TBL_COMMENT +
                ")";
        return mDB.query(TBL_COMMENT,null,whereclause,null,null,null,COl_COMMENT_TIMESTAMP + " DESC");
    }
}

• 需要注意的是时间戳列并没有被利用，但可能是，当添加了行（评论）当前时间戳就会自动被用来设置列。
• 注意getLatestComment和getAllButLatestComment方法返回游标与相应的行。

buyer home.Java

public class BuyerHome extends AppCompatActivity {

    EditText nameIn;
    EditText commentIn;
    TextView viewComment;
    Button postComment;
    ListView olderComments; //<<<<<<<<<< Added (Listview needs to be added to the layout)

    DatabaseHelper2 myDB;
    Cursor oldermessages, latestmessage; //<<<<<<<<<< Added
    SimpleCursorAdapter sma; //<<<<<<<<<< Added adapter for the ListView

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

        nameIn = (EditText) findViewById(R.id.nameInput);
        commentIn = (EditText) findViewById(R.id.commentText);
        viewComment = (TextView) findViewById(R.id.viewCommentText);
        olderComments = (ListView) findViewById(R.id.olderComments); //<<<<<<<<<< Added

        myDB = new DatabaseHelper2(this);
        postComment = (Button) findViewById(R.id.buttonComment);
        postComment.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String name = nameIn.getText().toString();
                String comment = commentIn.getText().toString();

                if (nameIn.length() != 0 && commentIn.length() != 0) {
                    myDB.addData(name, comment); //<<<<<<<<<< method starts changed lower case a
                    nameIn.setText("");
                    commentIn.setText("");
                } else {
                    Toast.makeText(BuyerHome.this, "Insert fields",
                            Toast.LENGTH_SHORT).show();
                }
                displayComments(); //<<<<<<<<<< added to refresh the display according to the latest comments
            }
        });
    }

    //<<<<<<<<<< ADDED so will display comments whenever called including returning from another activity
    @Override
    protected void onResume() {
        super.onResume();
        displayComments();
    }

    //<<<<<<<<<< ADDED entire method for displaying comments
    private void displayComments() {
        latestmessage = myDB.getLatestComment();
        if (latestmessage.moveToFirst()) {
            viewComment.setText(latestmessage.getString(latestmessage.getColumnIndex(DatabaseHelper2.COL_COMMENT_NAME)) +
                    " said :- " +
                    latestmessage.getString(latestmessage.getColumnIndex(DatabaseHelper2.COL_COMMENT_COMMENT)));
        } else {
            viewComment.setText("");
        }
        oldermessages = myDB.getAllButLatestComment();
        if (sma == null) {
            sma = new SimpleCursorAdapter(
                    this,
                    android.R.layout.simple_list_item_2,oldermessages,
                    new String[]{DatabaseHelper2.COL_COMMENT_NAME,DatabaseHelper2.COL_COMMENT_COMMENT},
                    new int[]{android.R.id.text1,android.R.id.text2},
                    0
            );
            olderComments.setAdapter(sma);
        } else {
            sma.swapCursor(oldermessages);
        }
    }
}

Result

• 该亮的行是最新的评论。
• 最新的评论之后是其他所有意见的列表。