无法在android中更改自定义editText的背景色

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.widget.EditText;

public class CustomEditText extends EditText {
    private Paint mPaint;

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

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

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

    private void init() {
        // 设置背景为透明
        setBackgroundColor(Color.TRANSPARENT);

        // 初始化画笔
        mPaint = new Paint();
        mPaint.setColor(Color.RED); // 设置背景色为红色
    }

    @Override
    protected void onDraw(Canvas canvas) {
        // 绘制背景色
        canvas.drawRect(0, 0, getWidth(), getHeight(), mPaint);

        super.onDraw(canvas);
    }
}

<com.example.CustomEditText
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Hello World!" />