下面是一个使用淡入淡出动画更改RelativeLayout背景图像的示例代码:

import android.animation.ObjectAnimator;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.view.animation.AlphaAnimation;
import android.view.animation.Animation;
import android.widget.RelativeLayout;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    private RelativeLayout mainLayout;

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

        mainLayout = findViewById(R.id.main_layout);

        // 设置初始背景图像
        Drawable initialDrawable = getResources().getDrawable(R.drawable.background_image);
        mainLayout.setBackground(initialDrawable);
        
        // 创建淡入淡出动画
        Animation fadeIn = new AlphaAnimation(0, 1);
        fadeIn.setDuration(1000);

        Animation fadeOut = new AlphaAnimation(1, 0);
        fadeOut.setDuration(1000);
        fadeOut.setStartOffset(1000); // 淡出动画开始前的延迟时间

        // 设置动画监听器
        fadeOut.setAnimationListener(new Animation.AnimationListener() {
            @Override
            public void onAnimationStart(Animation animation) {
                // 当淡出动画开始时，更改背景图像
                Drawable newDrawable = getResources().getDrawable(R.drawable.new_background_image);
                mainLayout.setBackground(newDrawable);
            }

            @Override
            public void onAnimationEnd(Animation animation) {
                // 动画结束时清除动画
                mainLayout.clearAnimation();
            }

            @Override
            public void onAnimationRepeat(Animation animation) {
                // 不需要实现
            }
        });

        // 应用淡入淡出动画
        mainLayout.startAnimation(fadeIn);
        mainLayout.startAnimation(fadeOut);
    }

}

上面的代码会将RelativeLayout的背景图像从background_image淡出，并在淡出动画开始时更改为new_background_image。