我不明白这句话试图用JAVA告诉我什么

Question

Here is the description of the problem I'm trying to solve:

The onProgressChanged method of the ToneGenerator class gets invoked whenever the user moves either of the two sliders. Verify this by running the application connected to your laptop and use the logging window to follow the onPress messages obtained from the log. What is the progress value obtained when the slider is all the way to the left and all the way to the right?

Since the same method is invoked regardless of which slider was moved, how can we determine the one that was moved? Hint: examine the parameters of the method.

One of the parameters sent to the method is seekBar, an object reference that points at the slider that was moved. Determine the ID of this object by using a method in its API (AndroidStudio helps with this once you type the object reference followed by a dot). Add a print statement at the top of the method to display this ID in Logcat.

Save the app and re-run it on the device. Move the sliders and note the displayed ID in the log.

The actual ID of any control can be obtained from the layout view. Add a second print statement at the top of the method to display the ID's of both sliders. Recall that you must prefix the XML ID with “R.id.” when you refer to it in Java. ”

I'm having problems with the last paragraph.

Here is the code :

package jr.eecs1022.tonegenerator;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.SeekBar;

public class ToneGenerator extends AppCompatActivity implements SeekBar.OnSeekBarChangeListener
{
    private ToneEmitter toneEmitter = null;

    public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser)
    {
        if (toneEmitter != null)
        {
            System.out.println();
            System.out.println(seekBar.getId());
            System.out.println("onPress called with " + progress);
        }
    }

    public void onStartTrackingTouch(SeekBar seekBar)
    {
    }

    public void onStopTrackingTouch(SeekBar seekBar)
    {
    }

    private void setFrequency(double frequency)
    {
        System.out.println("setFrequency called with " + frequency);
    }

    private void setAmplitude(double amplitude)
    {
        System.out.println("setAmplitude called with " + amplitude);
    }


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

        SeekBar seekbar = (SeekBar) findViewById(R.id.changeAmplitude);
        seekbar.setOnSeekBarChangeListener(this);
        seekbar = (SeekBar) findViewById(R.id.changeFrequency);
        seekbar.setOnSeekBarChangeListener(this);
    }

    @Override
    public void onResume()
    {
        super.onResume();
        toneEmitter = new ToneEmitter();
        this.setAmplitude(0.0);
        this.setFrequency(ToneEmitter.NOTE_C);
        SeekBar seekBar = (SeekBar) findViewById(R.id.changeAmplitude);
        seekBar.setProgress(0);
        seekBar = (SeekBar) findViewById(R.id.changeFrequency);
        seekBar.setProgress(0);
    }

    @Override
    public void onPause()
    {
        toneEmitter.shutdown();
        toneEmitter = null;
        super.onPause();
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu)
    {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_tone_generator, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item)
    {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings)
        {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

Answer 1

It means that you can refer to the id of any control by using the R class.

So, to try it out, it says you should add the following to the top of the onProgressChanged method:

System.out.println(R.id.slider1 + " " + R.id.slider2); //Use the actual id of the sliders