如何在ProgressBar上放置文本？

<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <ProgressBar
        android:id="@+id/progressBar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:progress="50"
        android:max="100"/>

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:text="50%"/>

</RelativeLayout>

public class TextProgressBarDrawable extends Drawable {

    private ProgressBar progressBar;
    private String text;

    public TextProgressBarDrawable(ProgressBar progressBar, String text) {
        this.progressBar = progressBar;
        this.text = text;
    }

    @Override
    public void draw(@NonNull Canvas canvas) {
        // 绘制ProgressBar
        progressBar.draw(canvas);

        // 绘制文本
        Paint paint = new Paint();
        paint.setColor(Color.BLACK);
        paint.setTextSize(24);
        paint.setTextAlign(Paint.Align.CENTER);
        canvas.drawText(text, canvas.getWidth() / 2, canvas.getHeight() / 2, paint);
    }

    @Override
    public void setAlpha(int alpha) {
        progressBar.setAlpha(alpha);
    }

    @Override
    public void setColorFilter(@Nullable ColorFilter colorFilter) {
        progressBar.setColorFilter(colorFilter);
    }

    @Override
    public int getOpacity() {
        return progressBar.getOpacity();
    }
}

ProgressBar progressBar = findViewById(R.id.progressBar);
String text = "50%";
TextProgressBarDrawable drawable = new TextProgressBarDrawable(progressBar, text);
progressBar.setProgressDrawable(drawable);

public class TextProgressBar extends ProgressBar {

    private TextView textView;

    public TextProgressBar(Context context) {
        super(context);
        init(context);
    }

    public TextProgressBar(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }

    public TextProgressBar(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context);
    }

    private void init(Context context) {
        textView = new TextView(context);
        textView.setLayoutParams(new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
        textView.setGravity(Gravity.CENTER);
        textView.setTextColor(Color.BLACK);
        addView(textView);
    }

    public void setText(String text) {
        textView.setText(text);
    }

}

<com.example.TextProgressBar
    android:id="@+id/textProgressBar"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:progress="50"
    android:max="100"/>

TextProgressBar textProgressBar = findViewById(R.id.textProgressBar);
textProgressBar.setText("50%");