java - 如何将数据从 Activity 传递到 Java 类

Question

我已经到达下面的墙了。我尝试将变量从我的主要 Activity 传递到生成数据库的 java 类，因为我想在该数据库的一个查询中使用此变量来获取结果，然后将其传递给主要 Activity 。这是我的代码:

//MainActivity

public class MainActivity extends AppCompatActivity {

    private static RadioGroup selectedAvgStds;
     ...... //rest of the code/// 


    public void onClickListenerButton(){


    selectedAvgStds = (RadioGroup)findViewById(R.id.controlAverageOfLiving);

    showResults.setOnClickListener(


        int avgStdLiving        = selectedAvgStds.getCheckedRadioButtonId();
        selectedAvgStdsRb       = (RadioButton) findViewById(avgStdLiving);

        //variable that  I want to pass 
        String avgStdLivingText = (String) selectedAvgStdsRb.getText();

        switch (option) {
           case "one":
               Intent intent = new Intent(MainActivity.this,DatabaseHelper.class);
               Intent.putExtra("values",avgStdLivingText);
               startActivity(intent);
           break;

          }
    );
}

我的数据库的一段代码

//DatabaseHelper
public class DatabaseHelper extends SQLiteOpenHelper{

public Cursor showResults(){

    SQLiteDatabase db = this.getWritableDatabase();

    //the intent does NOT work
    Bundle bundle = getIntent().getExtras();

    Cursor results = db.rawQuery("select * from "+TEMP_TABLE+"where value = " + selectedAvgStds , null);
    return results;
     }
}

尽管我已经导入了 Activity 和类中的所有 Intent 库，但 Intent 不起作用。我怎样才能实现我的目标？为什么 Intent 在这里不起作用？

任何建议和想法都将受到极大的赞赏。

Answer 1

根据您的评论，为什么不简单地将 DatabaseHelper 设为实例变量并参数化您的 showResults 方法，如下所示:

public class MyActivity extends Activity {

    private DatabaseHelper myDatabaseHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //initialise your helper here
        myDatabaseHelper = ...
    }

    public void onClickListenerButton(){

        // All your other stuff here...

        // variable that  I want to pass
        String avgStdLivingText = selectedAvgStdsRb.getText().toString();
        myDatabaseHelper.showResults(avgStdLivingText);
    }

}

然后在助手类中您可以简单地执行以下操作:

public Cursor showResults(String selectedAvgStds){
        SQLiteDatabase db = this.getWritableDatabase();

        Cursor results = db.rawQuery("select * from "+TEMP_TABLE+"where value = " + selectedAvgStds , null);
        return results;
     }
}