回答我自己的问题：在对Launcher3做了一些挖掘之后，我发现我需要在Touch Listener上使用WallpaperManager的sendWallpaperCommand函数来获得主屏幕视图：

import android.app.WallpaperManager;

private final int[] mTempXY = new int[2];
WallpaperManager mWallpaperManager = WallpaperManager.getInstance(context);

...

homeScreenView.setOnTouchListener((v, event) -> {
    onWallpaperTap(v,event);
    return true;
});

...

protected void onWallpaperTap(View view, MotionEvent ev) {
    final int[] position = mTempXY;
    view.getLocationOnScreen(position);

    int pointerIndex = ev.getActionIndex();
    position[0] += (int) ev.getX(pointerIndex);
    position[1] += (int) ev.getY(pointerIndex);

    MainActivity.mWallpaperManager.sendWallpaperCommand(view.getWindowToken(),
            ev.getAction() == MotionEvent.ACTION_UP
                    ? WallpaperManager.COMMAND_TAP : WallpaperManager.COMMAND_SECONDARY_TAP,
            position[0], position[1], 0, null);
}

而且现在我的壁纸可以接收触摸输入了。