定义构造函数

Question

“tapdb hon = new tapdb（this）;”中TapkeysActivity.java出错。它告诉定义构造函数tapdb（new View.OnClickListener（）{}）。请告诉我如何定义构造函数。相关代码如下：

TapkeysActivity.java

package com.android.tusway;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;


public class TapkeysActivity extends Activity  {


private EditText et;
private Button b1,b2,b3,b4,bspace;
private String stringDb="";
private TextView tv;


private void updateTextField() {
    tv.setText(this.stringDb);


}


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

        setContentView(R.layout.main);
        // adjusting key regarding window sizes

        et = (EditText) findViewById(R.id.editText1);

        b1 = (Button) findViewById(R.id.button1);
        b2 = (Button) findViewById(R.id.button2);
        b3 = (Button) findViewById(R.id.button3);
        b4 = (Button) findViewById(R.id.button4);
        bspace = (Button) findViewById(R.id.btspace);

        tv = (TextView) findViewById(R.id.textView1);

        b1.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                stringDb += "1";
                updateTextField();  

            }
        });


        b2.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                stringDb += "2";
                updateTextField();  

            }
        });

        b3.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                stringDb += "3";
                updateTextField();  

            }
        });

        b4.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                stringDb += "4";
                updateTextField();  

            }
        });

        bspace.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                stringDb += " ";
                updateTextField();


                long l = Long.parseLong(stringDb);
                tapdb hon = new tapdb(this);
                hon.open();
                String returnedWord = hon.getWord(l);

                hon.close();


                et.setText(returnedWord);


            }
        });

}
   }

tapdb.java

 package com.android.tusway;



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



 public class tapdb {

public static final String KEY_ROWID="_id";
public static final String KEY_CODE="key_code";
public static final String KEY_WORD="word";

public static final String DATABASE_NAME="tapdatabase";
public static final String DATABASE_TABLE="tapData";
public static final int DATABASE_VERSION=1;

private DbHelper ourHelper;
private final Context ourContext;
private SQLiteDatabase ourDatabase;

private static class DbHelper extends SQLiteOpenHelper{

    public DbHelper(Context context) {
        super(context,DATABASE_NAME, null, DATABASE_VERSION);

    }

    @Override
    public void onCreate(SQLiteDatabase db) {

        db.execSQL("CREATE TABLE" + DATABASE_TABLE + "(" +
                KEY_ROWID + "INTEGER PRIMARY KEY AUTOINCREAMENT,"+
                KEY_WORD + "TEXT NOT NULL" +
                KEY_CODE + "LONG);"

        );

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // TODO Auto-generated method stub
        db.execSQL("DROP TABLE IF EXISTS" + DATABASE_TABLE );
        onCreate(db);

    }

}
public tapdb (Context c) {
    ourContext = c;
  }


public tapdb open(){
    ourHelper = new DbHelper(ourContext);
    ourDatabase = ourHelper.getWritableDatabase();
    return this;
}

public void close(){
    ourHelper.close();

}





public String getWord(long l) {
    String[] columns = new String[] {KEY_ROWID, KEY_WORD, KEY_CODE};
    Cursor c = ourDatabase.query(DATABASE_TABLE, columns, KEY_ROWID + "=" + l, null, null, null, null);

    if (c != null) {
            c.moveToFirst();
            String hotness = c.getString(1);

            return hotness;
    }


    return null;
}

}

Answer 1

更改

tapdb hon = new tapdb(this);

到

tapdb hon = new tapdb(TapkeysActivity.this);

或

tapdb hon = new tapdb(v.getContext());

当您进入匿名内部课程时，this不会引用Actviity实例（在这种情况下，因为您在OnClickListener，this指的是您的{{ 1}}} instance）因此，您必须通过OnClickListener或TapkeysActivity.this明确地访问它。

Answer 2

更改此行，

tapdb hon = new tapdb(this);

与

tapdb hon = new tapdb(TapkeysActivity.this);